BPF-HELPERS(7) Miscellaneous Information Manual BPF-HELPERS(7)
NAME
BPF-HELPERS - list of eBPF helper functions
DESCRIPTION
The extended Berkeley Packet Filter (eBPF) subsystem consists in programs written in a pseudo-assembly language, then at‐
tached to one of the several kernel hooks and run in reaction of specific events. This framework differs from the older,
"classic" BPF (or "cBPF") in several aspects, one of them being the ability to call special functions (or "helpers") from
within a program. These functions are restricted to a white-list of helpers defined in the kernel.
These helpers are used by eBPF programs to interact with the system, or with the context in which they work. For instance,
they can be used to print debugging messages, to get the time since the system was booted, to interact with eBPF maps, or to
manipulate network packets. Since there are several eBPF program types, and that they do not run in the same context, each
program type can only call a subset of those helpers.
Due to eBPF conventions, a helper can not have more than five arguments.
Internally, eBPF programs call directly into the compiled helper functions without requiring any foreign-function interface.
As a result, calling helpers introduces no overhead, thus offering excellent performance.
This document is an attempt to list and document the helpers available to eBPF developers. They are sorted by chronological
order (the oldest helpers in the kernel at the top).
HELPERS
void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
Description
Perform a lookup in map for an entry associated to key.
Return Map value associated to key, or NULL if no entry was found.
long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
Description
Add or update the value of the entry associated to key in map with value. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for key.
Flag value BPF_NOEXIST cannot be used for maps of types BPF_MAP_TYPE_ARRAY or BPF_MAP_TYPE_PERCPU_ARRAY (all
elements always exist), the helper would return an error.
Return 0 on success, or a negative error in case of failure.
long bpf_map_delete_elem(struct bpf_map *map, const void *key)
Description
Delete entry with key from map.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read(void *dst, u32 size, const void *unsafe_ptr)
Description
For tracing programs, safely attempt to read size bytes from kernel space address unsafe_ptr and store the
data in dst.
Generally, use bpf_probe_read_user() or bpf_probe_read_kernel() instead.
Return 0 on success, or a negative error in case of failure.
u64 bpf_ktime_get_ns(void)
Description
Return the time elapsed since system boot, in nanoseconds. Does not include time the system was suspended.
See: clock_gettime(CLOCK_MONOTONIC)
Return Current ktime.
long bpf_trace_printk(const char *fmt, u32 fmt_size, ...)
Description
This helper is a "printk()-like" facility for debugging. It prints a message defined by format fmt (of size
fmt_size) to file /sys/kernel/debug/tracing/trace from DebugFS, if available. It can take up to three addi‐
tional u64 arguments (as an eBPF helpers, the total number of arguments is limited to five).
Each time the helper is called, it appends a line to the trace. Lines are discarded while /sys/kernel/de‐
bug/tracing/trace is open, use /sys/kernel/debug/tracing/trace_pipe to avoid this. The format of the trace is
customizable, and the exact output one will get depends on the options set in /sys/kernel/debug/trac‐
ing/trace_options (see also the README file under the same directory). However, it usually defaults to some‐
thing like:
telnet-470 [001] .N.. 419421.045894: 0x00000001: <formatted msg>
In the above:
• telnet is the name of the current task.
• 470 is the PID of the current task.
• 001 is the CPU number on which the task is running.
• In .N.., each character refers to a set of options (whether irqs are enabled, scheduling options, whether
hard/softirqs are running, level of preempt_disabled respectively). N means that TIF_NEED_RESCHED and
PREEMPT_NEED_RESCHED are set.
• 419421.045894 is a timestamp.
• 0x00000001 is a fake value used by BPF for the instruction pointer register.
• <formatted msg> is the message formatted with fmt.
The conversion specifiers supported by fmt are similar, but more limited than for printk(). They are %d, %i,
%u, %x, %ld, %li, %lu, %lx, %lld, %lli, %llu, %llx, %p, %s. No modifier (size of field, padding with zeroes,
etc.) is available, and the helper will return -EINVAL (but print nothing) if it encounters an unknown speci‐
fier.
Also, note that bpf_trace_printk() is slow, and should only be used for debugging purposes. For this reason, a
notice block (spanning several lines) is printed to kernel logs and states that the helper should not be used
"for production use" the first time this helper is used (or more precisely, when trace_printk() buffers are
allocated). For passing values to user space, perf events should be preferred.
Return The number of bytes written to the buffer, or a negative error in case of failure.
u32 bpf_get_prandom_u32(void)
Description
Get a pseudo-random number.
From a security point of view, this helper uses its own pseudo-random internal state, and cannot be used to
infer the seed of other random functions in the kernel. However, it is essential to note that the generator
used by the helper is not cryptographically secure.
Return A random 32-bit unsigned value.
u32 bpf_get_smp_processor_id(void)
Description
Get the SMP (symmetric multiprocessing) processor id. Note that all programs run with migration disabled,
which means that the SMP processor id is stable during all the execution of the program.
Return The SMP id of the processor running the program.
long bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len, u64 flags)
Description
Store len bytes from address from into the packet associated to skb, at offset. flags are a combination of
BPF_F_RECOMPUTE_CSUM (automatically recompute the checksum for the packet after storing the bytes) and
BPF_F_INVALIDATE_HASH (set skb->hash, skb->swhash and skb->l4hash to 0).
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to, u64 size)
Description
Recompute the layer 3 (e.g. IP) checksum for the packet associated to skb. Computation is incremental, so the
helper must know the former value of the header field that was modified (from), the new value of this field
(to), and the number of bytes (2 or 4) for this field, stored in size. Alternatively, it is possible to store
the difference between the previous and the new values of the header field in to, by setting from and size to
0. For both methods, offset indicates the location of the IP checksum within the packet.
This helper works in combination with bpf_csum_diff(), which does not update the checksum in-place, but offers
more flexibility and can handle sizes larger than 2 or 4 for the checksum to update.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to, u64 flags)
Description
Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum for the packet associated to skb. Computation is incre‐
mental, so the helper must know the former value of the header field that was modified (from), the new value
of this field (to), and the number of bytes (2 or 4) for this field, stored on the lowest four bits of flags.
Alternatively, it is possible to store the difference between the previous and the new values of the header
field in to, by setting from and the four lowest bits of flags to 0. For both methods, offset indicates the
location of the IP checksum within the packet. In addition to the size of the field, flags can be added (bit‐
wise OR) actual flags. With BPF_F_MARK_MANGLED_0, a null checksum is left untouched (unless BPF_F_MARK_ENFORCE
is added as well), and for updates resulting in a null checksum the value is set to CSUM_MANGLED_0 instead.
Flag BPF_F_PSEUDO_HDR indicates the checksum is to be computed against a pseudo-header.
This helper works in combination with bpf_csum_diff(), which does not update the checksum in-place, but offers
more flexibility and can handle sizes larger than 2 or 4 for the checksum to update.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32 index)
Description
This special helper is used to trigger a "tail call", or in other words, to jump into another eBPF program.
The same stack frame is used (but values on stack and in registers for the caller are not accessible to the
callee). This mechanism allows for program chaining, either for raising the maximum number of available eBPF
instructions, or to execute given programs in conditional blocks. For security reasons, there is an upper
limit to the number of successive tail calls that can be performed.
Upon call of this helper, the program attempts to jump into a program referenced at index index in prog_ar‐
ray_map, a special map of type BPF_MAP_TYPE_PROG_ARRAY, and passes ctx, a pointer to the context.
If the call succeeds, the kernel immediately runs the first instruction of the new program. This is not a
function call, and it never returns to the previous program. If the call fails, then the helper has no effect,
and the caller continues to run its subsequent instructions. A call can fail if the destination program for
the jump does not exist (i.e. index is superior to the number of entries in prog_array_map), or if the maximum
number of tail calls has been reached for this chain of programs. This limit is defined in the kernel by the
macro MAX_TAIL_CALL_CNT (not accessible to user space), which is currently set to 33.
Return 0 on success, or a negative error in case of failure.
long bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)
Description
Clone and redirect the packet associated to skb to another net device of index ifindex. Both ingress and
egress interfaces can be used for redirection. The BPF_F_INGRESS value in flags is used to make the distinc‐
tion (ingress path is selected if the flag is present, egress path otherwise). This is the only flag sup‐
ported for now.
In comparison with bpf_redirect() helper, bpf_clone_redirect() has the associated cost of duplicating the
packet buffer, but this can be executed out of the eBPF program. Conversely, bpf_redirect() is more efficient,
but it is handled through an action code where the redirection happens only after the eBPF program has re‐
turned.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
u64 bpf_get_current_pid_tgid(void)
Description
Get the current pid and tgid.
Return A 64-bit integer containing the current tgid and pid, and created as such: current_task->tgid << 32 | cur‐
rent_task->pid.
u64 bpf_get_current_uid_gid(void)
Description
Get the current uid and gid.
Return A 64-bit integer containing the current GID and UID, and created as such: current_gid << 32 | current_uid.
long bpf_get_current_comm(void *buf, u32 size_of_buf)
Description
Copy the comm attribute of the current task into buf of size_of_buf. The comm attribute contains the name of
the executable (excluding the path) for the current task. The size_of_buf must be strictly positive. On suc‐
cess, the helper makes sure that the buf is NUL-terminated. On failure, it is filled with zeroes.
Return 0 on success, or a negative error in case of failure.
u32 bpf_get_cgroup_classid(struct sk_buff *skb)
Description
Retrieve the classid for the current task, i.e. for the net_cls cgroup to which skb belongs.
This helper can be used on TC egress path, but not on ingress.
The net_cls cgroup provides an interface to tag network packets based on a user-provided identifier for all
traffic coming from the tasks belonging to the related cgroup. See also the related kernel documentation,
available from the Linux sources in file Documentation/admin-guide/cgroup-v1/net_cls.rst.
The Linux kernel has two versions for cgroups: there are cgroups v1 and cgroups v2. Both are available to
users, who can use a mixture of them, but note that the net_cls cgroup is for cgroup v1 only. This makes it
incompatible with BPF programs run on cgroups, which is a cgroup-v2-only feature (a socket can only hold data
for one version of cgroups at a time).
This helper is only available is the kernel was compiled with the CONFIG_CGROUP_NET_CLASSID configuration op‐
tion set to "y" or to "m".
Return The classid, or 0 for the default unconfigured classid.
long bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
Description
Push a vlan_tci (VLAN tag control information) of protocol vlan_proto to the packet associated to skb, then
update the checksum. Note that if vlan_proto is different from ETH_P_8021Q and ETH_P_8021AD, it is considered
to be ETH_P_8021Q.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_vlan_pop(struct sk_buff *skb)
Description
Pop a VLAN header from the packet associated to skb.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key, u32 size, u64 flags)
Description
Get tunnel metadata. This helper takes a pointer key to an empty struct bpf_tunnel_key of size, that will be
filled with tunnel metadata for the packet associated to skb. The flags can be set to BPF_F_TUNINFO_IPV6,
which indicates that the tunnel is based on IPv6 protocol instead of IPv4.
The struct bpf_tunnel_key is an object that generalizes the principal parameters used by various tunneling
protocols into a single struct. This way, it can be used to easily make a decision based on the contents of
the encapsulation header, "summarized" in this struct. In particular, it holds the IP address of the remote
end (IPv4 or IPv6, depending on the case) in key->remote_ipv4 or key->remote_ipv6. Also, this struct exposes
the key->tunnel_id, which is generally mapped to a VNI (Virtual Network Identifier), making it programmable
together with the bpf_skb_set_tunnel_key() helper.
Let's imagine that the following code is part of a program attached to the TC ingress interface, on one end of
a GRE tunnel, and is supposed to filter out all messages coming from remote ends with IPv4 address other than
10.0.0.1:
int ret;
struct bpf_tunnel_key key = {};
ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
if (ret < 0)
return TC_ACT_SHOT; // drop packet
if (key.remote_ipv4 != 0x0a000001)
return TC_ACT_SHOT; // drop packet
return TC_ACT_OK; // accept packet
This interface can also be used with all encapsulation devices that can operate in "collect metadata" mode:
instead of having one network device per specific configuration, the "collect metadata" mode only requires a
single device where the configuration can be extracted from this helper.
This can be used together with various tunnels such as VXLan, Geneve, GRE or IP in IP (IPIP).
Return 0 on success, or a negative error in case of failure.
long bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key, u32 size, u64 flags)
Description
Populate tunnel metadata for packet associated to skb. The tunnel metadata is set to the contents of key, of
size. The flags can be set to a combination of the following values:
BPF_F_TUNINFO_IPV6
Indicate that the tunnel is based on IPv6 protocol instead of IPv4.
BPF_F_ZERO_CSUM_TX
For IPv4 packets, add a flag to tunnel metadata indicating that checksum computation should be skipped
and checksum set to zeroes.
BPF_F_DONT_FRAGMENT
Add a flag to tunnel metadata indicating that the packet should not be fragmented.
BPF_F_SEQ_NUMBER
Add a flag to tunnel metadata indicating that a sequence number should be added to tunnel header before
sending the packet. This flag was added for GRE encapsulation, but might be used with other protocols
as well in the future.
Here is a typical usage on the transmit path:
struct bpf_tunnel_key key;
populate key ...
bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);
See also the description of the bpf_skb_get_tunnel_key() helper for additional information.
Return 0 on success, or a negative error in case of failure.
u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)
Description
Read the value of a perf event counter. This helper relies on a map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. The
nature of the perf event counter is selected when map is updated with perf event file descriptors. The map is
an array whose size is the number of available CPUs, and each cell contains a value relative to one CPU. The
value to retrieve is indicated by flags, that contains the index of the CPU to look up, masked with BPF_F_IN‐
DEX_MASK. Alternatively, flags can be set to BPF_F_CURRENT_CPU to indicate that the value for the current CPU
should be retrieved.
Note that before Linux 4.13, only hardware perf event can be retrieved.
Also, be aware that the newer helper bpf_perf_event_read_value() is recommended over bpf_perf_event_read() in
general. The latter has some ABI quirks where error and counter value are used as a return code (which is
wrong to do since ranges may overlap). This issue is fixed with bpf_perf_event_read_value(), which at the same
time provides more features over the bpf_perf_event_read() interface. Please refer to the description of
bpf_perf_event_read_value() for details.
Return The value of the perf event counter read from the map, or a negative error code in case of failure.
long bpf_redirect(u32 ifindex, u64 flags)
Description
Redirect the packet to another net device of index ifindex. This helper is somewhat similar to bpf_clone_re‐
direct(), except that the packet is not cloned, which provides increased performance.
Except for XDP, both ingress and egress interfaces can be used for redirection. The BPF_F_INGRESS value in
flags is used to make the distinction (ingress path is selected if the flag is present, egress path other‐
wise). Currently, XDP only supports redirection to the egress interface, and accepts no flag at all.
The same effect can also be attained with the more generic bpf_redirect_map(), which uses a BPF map to store
the redirect target instead of providing it directly to the helper.
Return For XDP, the helper returns XDP_REDIRECT on success or XDP_ABORTED on error. For other program types, the val‐
ues are TC_ACT_REDIRECT on success or TC_ACT_SHOT on error.
u32 bpf_get_route_realm(struct sk_buff *skb)
Description
Retrieve the realm or the route, that is to say the tclassid field of the destination for the skb. The identi‐
fier retrieved is a user-provided tag, similar to the one used with the net_cls cgroup (see description for
bpf_get_cgroup_classid() helper), but here this tag is held by a route (a destination entry), not by a task.
Retrieving this identifier works with the clsact TC egress hook (see also tc-bpf(8)), or alternatively on con‐
ventional classful egress qdiscs, but not on TC ingress path. In case of clsact TC egress hook, this has the
advantage that, internally, the destination entry has not been dropped yet in the transmit path. Therefore,
the destination entry does not need to be artificially held via netif_keep_dst() for a classful qdisc until
the skb is freed.
This helper is available only if the kernel was compiled with CONFIG_IP_ROUTE_CLASSID configuration option.
Return The realm of the route for the packet associated to skb, or 0 if none was found.
long bpf_perf_event_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)
Description
Write raw data blob into a special BPF perf event held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes: PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type, and
PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for which the value must be put, masked with BPF_F_INDEX_MASK.
Alternatively, flags can be set to BPF_F_CURRENT_CPU to indicate that the index of the current CPU core should
be used.
The value to write, of size, is passed through eBPF stack and pointed by data.
The context of the program ctx needs also be passed to the helper.
On user space, a program willing to read the values needs to call perf_event_open() on the perf event (either
for one or for all CPUs) and to store the file descriptor into the map. This must be done before the eBPF pro‐
gram can send data into it. An example is available in file samples/bpf/trace_output_user.c in the Linux ker‐
nel source tree (the eBPF program counterpart is in samples/bpf/trace_output_kern.c).
bpf_perf_event_output() achieves better performance than bpf_trace_printk() for sharing data with user space,
and is much better suitable for streaming data from eBPF programs.
Note that this helper is not restricted to tracing use cases and can be used with programs attached to TC or
XDP as well, where it allows for passing data to user space listeners. Data can be:
• Only custom structs,
• Only the packet payload, or
• A combination of both.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_load_bytes(const void *skb, u32 offset, void *to, u32 len)
Description
This helper was provided as an easy way to load data from a packet. It can be used to load len bytes from off‐
set from the packet associated to skb, into the buffer pointed by to.
Since Linux 4.7, usage of this helper has mostly been replaced by "direct packet access", enabling packet data
to be manipulated with skb->data and skb->data_end pointing respectively to the first byte of packet data and
to the byte after the last byte of packet data. However, it remains useful if one wishes to read large quanti‐
ties of data at once from a packet into the eBPF stack.
Return 0 on success, or a negative error in case of failure.
long bpf_get_stackid(void *ctx, struct bpf_map *map, u64 flags)
Description
Walk a user or a kernel stack and return its id. To achieve this, the helper needs ctx, which is a pointer to
the context on which the tracing program is executed, and a pointer to a map of type BPF_MAP_TYPE_STACK_TRACE.
The last argument, flags, holds the number of stack frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set a combination of the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel stack.
BPF_F_FAST_STACK_CMP
Compare stacks by hash only.
BPF_F_REUSE_STACKID
If two different stacks hash into the same stackid, discard the old one.
The stack id retrieved is a 32 bit long integer handle which can be further combined with other data (includ‐
ing other stack ids) and used as a key into maps. This can be useful for generating a variety of graphs (such
as flame graphs or off-cpu graphs).
For walking a stack, this helper is an improvement over bpf_probe_read(), which can be used with unrolled
loops but is not efficient and consumes a lot of eBPF instructions. Instead, bpf_get_stackid() can collect up
to PERF_MAX_STACK_DEPTH both kernel and user frames. Note that this limit can be controlled with the sysctl
program, and that it should be manually increased in order to profile long user stacks (such as stacks for
Java programs). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The positive or null stack id on success, or a negative error in case of failure.
s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32 to_size, __wsum seed)
Description
Compute a checksum difference, from the raw buffer pointed by from, of length from_size (that must be a multi‐
ple of 4), towards the raw buffer pointed by to, of size to_size (same remark). An optional seed can be added
to the value (this can be cascaded, the seed may come from a previous call to the helper).
This is flexible enough to be used in several ways:
• With from_size == 0, to_size > 0 and seed set to checksum, it can be used when pushing new data.
• With from_size > 0, to_size == 0 and seed set to checksum, it can be used when removing data from a packet.
• With from_size > 0, to_size > 0 and seed set to 0, it can be used to compute a diff. Note that from_size and
to_size do not need to be equal.
This helper can be used in combination with bpf_l3_csum_replace() and bpf_l4_csum_replace(), to which one can
feed in the difference computed with bpf_csum_diff().
Return The checksum result, or a negative error code in case of failure.
long bpf_skb_get_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
Description
Retrieve tunnel options metadata for the packet associated to skb, and store the raw tunnel option data to the
buffer opt of size.
This helper can be used with encapsulation devices that can operate in "collect metadata" mode (please refer
to the related note in the description of bpf_skb_get_tunnel_key() for more details). A particular example
where this can be used is in combination with the Geneve encapsulation protocol, where it allows for pushing
(with bpf_skb_get_tunnel_opt() helper) and retrieving arbitrary TLVs (Type-Length-Value headers) from the eBPF
program. This allows for full customization of these headers.
Return The size of the option data retrieved.
long bpf_skb_set_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
Description
Set tunnel options metadata for the packet associated to skb to the option data contained in the raw buffer
opt of size.
See also the description of the bpf_skb_get_tunnel_opt() helper for additional information.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64 flags)
Description
Change the protocol of the skb to proto. Currently supported are transition from IPv4 to IPv6, and from IPv6
to IPv4. The helper takes care of the groundwork for the transition, including resizing the socket buffer. The
eBPF program is expected to fill the new headers, if any, via skb_store_bytes() and to recompute the checksums
with bpf_l3_csum_replace() and bpf_l4_csum_replace(). The main case for this helper is to perform NAT64 opera‐
tions out of an eBPF program.
Internally, the GSO type is marked as dodgy so that headers are checked and segments are recalculated by the
GSO/GRO engine. The size for GSO target is adapted as well.
All values for flags are reserved for future usage, and must be left at zero.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_change_type(struct sk_buff *skb, u32 type)
Description
Change the packet type for the packet associated to skb. This comes down to setting skb->pkt_type to type, ex‐
cept the eBPF program does not have a write access to skb->pkt_type beside this helper. Using a helper here
allows for graceful handling of errors.
The major use case is to change incoming skb*s to **PACKET_HOST* in a programmatic way instead of having to
recirculate via redirect(..., BPF_F_INGRESS), for example.
Note that type only allows certain values. At this time, they are:
PACKET_HOST
Packet is for us.
PACKET_BROADCAST
Send packet to all.
PACKET_MULTICAST
Send packet to group.
PACKET_OTHERHOST
Send packet to someone else.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map, u32 index)
Description
Check whether skb is a descendant of the cgroup2 held by map of type BPF_MAP_TYPE_CGROUP_ARRAY, at index.
Return The return value depends on the result of the test, and can be:
• 0, if the skb failed the cgroup2 descendant test.
• 1, if the skb succeeded the cgroup2 descendant test.
• A negative error code, if an error occurred.
u32 bpf_get_hash_recalc(struct sk_buff *skb)
Description
Retrieve the hash of the packet, skb->hash. If it is not set, in particular if the hash was cleared due to
mangling, recompute this hash. Later accesses to the hash can be done directly with skb->hash.
Calling bpf_set_hash_invalid(), changing a packet prototype with bpf_skb_change_proto(), or calling
bpf_skb_store_bytes() with the BPF_F_INVALIDATE_HASH are actions susceptible to clear the hash and to trigger
a new computation for the next call to bpf_get_hash_recalc().
Return The 32-bit hash.
u64 bpf_get_current_task(void)
Description
Get the current task.
Return A pointer to the current task struct.
long bpf_probe_write_user(void *dst, const void *src, u32 len)
Description
Attempt in a safe way to write len bytes from the buffer src to dst in memory. It only works for threads that
are in user context, and dst must be a valid user space address.
This helper should not be used to implement any kind of security mechanism because of TOC-TOU attacks, but
rather to debug, divert, and manipulate execution of semi-cooperative processes.
Keep in mind that this feature is meant for experiments, and it has a risk of crashing the system and running
programs. Therefore, when an eBPF program using this helper is attached, a warning including PID and process
name is printed to kernel logs.
Return 0 on success, or a negative error in case of failure.
long bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)
Description
Check whether the probe is being run is the context of a given subset of the cgroup2 hierarchy. The cgroup2 to
test is held by map of type BPF_MAP_TYPE_CGROUP_ARRAY, at index.
Return The return value depends on the result of the test, and can be:
• 1, if current task belongs to the cgroup2.
• 0, if current task does not belong to the cgroup2.
• A negative error code, if an error occurred.
long bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)
Description
Resize (trim or grow) the packet associated to skb to the new len. The flags are reserved for future usage,
and must be left at zero.
The basic idea is that the helper performs the needed work to change the size of the packet, then the eBPF
program rewrites the rest via helpers like bpf_skb_store_bytes(), bpf_l3_csum_replace(), bpf_l3_csum_replace()
and others. This helper is a slow path utility intended for replies with control messages. And because it is
targeted for slow path, the helper itself can afford to be slow: it implicitly linearizes, unclones and drops
offloads from the skb.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_pull_data(struct sk_buff *skb, u32 len)
Description
Pull in non-linear data in case the skb is non-linear and not all of len are part of the linear section. Make
len bytes from skb readable and writable. If a zero value is passed for len, then all bytes in the linear part
of skb will be made readable and writable.
This helper is only needed for reading and writing with direct packet access.
For direct packet access, testing that offsets to access are within packet boundaries (test on skb->data_end)
is susceptible to fail if offsets are invalid, or if the requested data is in non-linear parts of the skb. On
failure the program can just bail out, or in the case of a non-linear buffer, use a helper to make the data
available. The bpf_skb_load_bytes() helper is a first solution to access the data. Another one consists in us‐
ing bpf_skb_pull_data to pull in once the non-linear parts, then retesting and eventually access the data.
At the same time, this also makes sure the skb is uncloned, which is a necessary condition for direct write.
As this needs to be an invariant for the write part only, the verifier detects writes and adds a prologue that
is calling bpf_skb_pull_data() to effectively unclone the skb from the very beginning in case it is indeed
cloned.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)
Description
Add the checksum csum into skb->csum in case the driver has supplied a checksum for the entire packet into
that field. Return an error otherwise. This helper is intended to be used in combination with bpf_csum_diff(),
in particular when the checksum needs to be updated after data has been written into the packet through direct
packet access.
Return The checksum on success, or a negative error code in case of failure.
void bpf_set_hash_invalid(struct sk_buff *skb)
Description
Invalidate the current skb->hash. It can be used after mangling on headers through direct packet access, in
order to indicate that the hash is outdated and to trigger a recalculation the next time the kernel tries to
access this hash or when the bpf_get_hash_recalc() helper is called.
Return void.
long bpf_get_numa_node_id(void)
Description
Return the id of the current NUMA node. The primary use case for this helper is the selection of sockets for
the local NUMA node, when the program is attached to sockets using the SO_ATTACH_REUSEPORT_EBPF option (see
also socket(7)), but the helper is also available to other eBPF program types, similarly to bpf_get_smp_pro‐
cessor_id().
Return The id of current NUMA node.
long bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)
Description
Grows headroom of packet associated to skb and adjusts the offset of the MAC header accordingly, adding len
bytes of space. It automatically extends and reallocates memory as required.
This helper can be used on a layer 3 skb to push a MAC header for redirection into a layer 2 device.
All values for flags are reserved for future usage, and must be left at zero.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)
Description
Adjust (move) xdp_md->data by delta bytes. Note that it is possible to use a negative value for delta. This
helper can be used to prepare the packet for pushing or popping headers.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_str(void *dst, u32 size, const void *unsafe_ptr)
Description
Copy a NUL terminated string from an unsafe kernel address unsafe_ptr to dst. See bpf_probe_read_kernel_str()
for more details.
Generally, use bpf_probe_read_user_str() or bpf_probe_read_kernel_str() instead.
Return On success, the strictly positive length of the string, including the trailing NUL character. On error, a neg‐
ative value.
u64 bpf_get_socket_cookie(struct sk_buff *skb)
Description
If the struct sk_buff pointed by skb has a known socket, retrieve the cookie (generated by the kernel) of this
socket. If no cookie has been set yet, generate a new cookie. Once generated, the socket cookie remains sta‐
ble for the life of the socket. This helper can be useful for monitoring per socket networking traffic statis‐
tics as it provides a global socket identifier that can be assumed unique.
Return A 8-byte long unique number on success, or 0 if the socket field is missing inside skb.
u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)
Description
Equivalent to bpf_get_socket_cookie() helper that accepts skb, but gets socket from struct bpf_sock_addr con‐
text.
Return A 8-byte long unique number.
u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)
Description
Equivalent to bpf_get_socket_cookie() helper that accepts skb, but gets socket from struct bpf_sock_ops con‐
text.
Return A 8-byte long unique number.
u64 bpf_get_socket_cookie(struct sock *sk)
Description
Equivalent to bpf_get_socket_cookie() helper that accepts sk, but gets socket from a BTF struct sock. This
helper also works for sleepable programs.
Return A 8-byte long unique number or 0 if sk is NULL.
u32 bpf_get_socket_uid(struct sk_buff *skb)
Description
Get the owner UID of the socked associated to skb.
Return The owner UID of the socket associated to skb. If the socket is NULL, or if it is not a full socket (i.e. if
it is a time-wait or a request socket instead), overflowuid value is returned (note that overflowuid might
also be the actual UID value for the socket).
long bpf_set_hash(struct sk_buff *skb, u32 hash)
Description
Set the full hash for skb (set the field skb->hash) to value hash.
Return 0
long bpf_setsockopt(void *bpf_socket, int level, int optname, void *optval, int optlen)
Description
Emulate a call to setsockopt() on the socket associated to bpf_socket, which must be a full socket. The level
at which the option resides and the name optname of the option must be specified, see setsockopt(2) for more
information. The option value of length optlen is pointed by optval.
bpf_socket should be one of the following:
• struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.
• struct bpf_sock_addr for BPF_CGROUP_INET4_CONNECT and BPF_CGROUP_INET6_CONNECT.
This helper actually implements a subset of setsockopt(). It supports the following levels:
• SOL_SOCKET, which supports the following optnames: SO_RCVBUF, SO_SNDBUF, SO_MAX_PACING_RATE, SO_PRIORITY,
SO_RCVLOWAT, SO_MARK, SO_BINDTODEVICE, SO_KEEPALIVE.
• IPPROTO_TCP, which supports the following optnames: TCP_CONGESTION, TCP_BPF_IW, TCP_BPF_SNDCWND_CLAMP,
TCP_SAVE_SYN, TCP_KEEPIDLE, TCP_KEEPINTVL, TCP_KEEPCNT, TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT.
• IPPROTO_IP, which supports optname IP_TOS.
• IPPROTO_IPV6, which supports optname IPV6_TCLASS.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode, u64 flags)
Description
Grow or shrink the room for data in the packet associated to skb by len_diff, and according to the selected
mode.
By default, the helper will reset any offloaded checksum indicator of the skb to CHECKSUM_NONE. This can be
avoided by the following flag:
• BPF_F_ADJ_ROOM_NO_CSUM_RESET: Do not reset offloaded checksum data of the skb to CHECKSUM_NONE.
There are two supported modes at this time:
• BPF_ADJ_ROOM_MAC: Adjust room at the mac layer (room space is added or removed between the layer 2 and layer
3 headers).
• BPF_ADJ_ROOM_NET: Adjust room at the network layer (room space is added or removed between the layer 3 and
layer 4 headers).
The following flags are supported at this time:
• BPF_F_ADJ_ROOM_FIXED_GSO: Do not adjust gso_size. Adjusting mss in this way is not allowed for datagrams.
• BPF_F_ADJ_ROOM_ENCAP_L3_IPV4, BPF_F_ADJ_ROOM_ENCAP_L3_IPV6: Any new space is reserved to hold a tunnel
header. Configure skb offsets and other fields accordingly.
• BPF_F_ADJ_ROOM_ENCAP_L4_GRE, BPF_F_ADJ_ROOM_ENCAP_L4_UDP: Use with ENCAP_L3 flags to further specify the
tunnel type.
• BPF_F_ADJ_ROOM_ENCAP_L2(len): Use with ENCAP_L3/L4 flags to further specify the tunnel type; len is the
length of the inner MAC header.
• BPF_F_ADJ_ROOM_ENCAP_L2_ETH: Use with BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the L2 type as Ether‐
net.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)
Description
Redirect the packet to the endpoint referenced by map at index key. Depending on its type, this map can con‐
tain references to net devices (for forwarding packets through other ports), or to CPUs (for redirecting XDP
frames to another CPU; but this is only implemented for native XDP (with driver support) as of this writing).
The lower two bits of flags are used as the return code if the map lookup fails. This is so that the return
value can be one of the XDP program return codes up to XDP_TX, as chosen by the caller. The higher bits of
flags can be set to BPF_F_BROADCAST or BPF_F_EXCLUDE_INGRESS as defined below.
With BPF_F_BROADCAST the packet will be broadcasted to all the interfaces in the map, with BPF_F_EX‐
CLUDE_INGRESS the ingress interface will be excluded when do broadcasting.
See also bpf_redirect(), which only supports redirecting to an ifindex, but doesn't require a map to do so.
Return XDP_REDIRECT on success, or the value of the two lower bits of the flags argument on error.
long bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key, u64 flags)
Description
Redirect the packet to the socket referenced by map (of type BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress
and egress interfaces can be used for redirection. The BPF_F_INGRESS value in flags is used to make the dis‐
tinction (ingress path is selected if the flag is present, egress path otherwise). This is the only flag sup‐
ported for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
Description
Add an entry to, or update a map referencing sockets. The skops is used as a new value for the entry associ‐
ated to key. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for key.
If the map has eBPF programs (parser and verdict), those will be inherited by the socket being added. If the
socket is already attached to eBPF programs, this results in an error.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)
Description
Adjust the address pointed by xdp_md->data_meta by delta (which can be positive or negative). Note that this
operation modifies the address stored in xdp_md->data, so the latter must be loaded only after the helper has
been called.
The use of xdp_md->data_meta is optional and programs are not required to use it. The rationale is that when
the packet is processed with XDP (e.g. as DoS filter), it is possible to push further meta data along with it
before passing to the stack, and to give the guarantee that an ingress eBPF program attached as a TC classi‐
fier on the same device can pick this up for further post-processing. Since TC works with socket buffers, it
remains possible to set from XDP the mark or priority pointers, or other pointers for the socket buffer. Hav‐
ing this scratch space generic and programmable allows for more flexibility as the user is free to store what‐
ever meta data they need.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct bpf_perf_event_value *buf, u32 buf_size)
Description
Read the value of a perf event counter, and store it into buf of size buf_size. This helper relies on a map of
type BPF_MAP_TYPE_PERF_EVENT_ARRAY. The nature of the perf event counter is selected when map is updated with
perf event file descriptors. The map is an array whose size is the number of available CPUs, and each cell
contains a value relative to one CPU. The value to retrieve is indicated by flags, that contains the index of
the CPU to look up, masked with BPF_F_INDEX_MASK. Alternatively, flags can be set to BPF_F_CURRENT_CPU to in‐
dicate that the value for the current CPU should be retrieved.
This helper behaves in a way close to bpf_perf_event_read() helper, save that instead of just returning the
value observed, it fills the buf structure. This allows for additional data to be retrieved: in particular,
the enabled and running times (in buf->enabled and buf->running, respectively) are copied. In general,
bpf_perf_event_read_value() is recommended over bpf_perf_event_read(), which has some ABI issues and provides
fewer functionalities.
These values are interesting, because hardware PMU (Performance Monitoring Unit) counters are limited re‐
sources. When there are more PMU based perf events opened than available counters, kernel will multiplex these
events so each event gets certain percentage (but not all) of the PMU time. In case that multiplexing happens,
the number of samples or counter value will not reflect the case compared to when no multiplexing occurs. This
makes comparison between different runs difficult. Typically, the counter value should be normalized before
comparing to other experiments. The usual normalization is done as follows.
normalized_counter = counter * t_enabled / t_running
Where t_enabled is the time enabled for event and t_running is the time running for event since last normal‐
ization. The enabled and running times are accumulated since the perf event open. To achieve scaling factor
between two invocations of an eBPF program, users can use CPU id as the key (which is typical for perf array
usage model) to remember the previous value and do the calculation inside the eBPF program.
Return 0 on success, or a negative error in case of failure.
long bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, struct bpf_perf_event_value *buf, u32 buf_size)
Description
For en eBPF program attached to a perf event, retrieve the value of the event counter associated to ctx and
store it in the structure pointed by buf and of size buf_size. Enabled and running times are also stored in
the structure (see description of helper bpf_perf_event_read_value() for more details).
Return 0 on success, or a negative error in case of failure.
long bpf_getsockopt(void *bpf_socket, int level, int optname, void *optval, int optlen)
Description
Emulate a call to getsockopt() on the socket associated to bpf_socket, which must be a full socket. The level
at which the option resides and the name optname of the option must be specified, see getsockopt(2) for more
information. The retrieved value is stored in the structure pointed by opval and of length optlen.
bpf_socket should be one of the following:
• struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.
• struct bpf_sock_addr for BPF_CGROUP_INET4_CONNECT and BPF_CGROUP_INET6_CONNECT.
This helper actually implements a subset of getsockopt(). It supports the following levels:
• IPPROTO_TCP, which supports optname TCP_CONGESTION.
• IPPROTO_IP, which supports optname IP_TOS.
• IPPROTO_IPV6, which supports optname IPV6_TCLASS.
Return 0 on success, or a negative error in case of failure.
long bpf_override_return(struct pt_regs *regs, u64 rc)
Description
Used for error injection, this helper uses kprobes to override the return value of the probed function, and to
set it to rc. The first argument is the context regs on which the kprobe works.
This helper works by setting the PC (program counter) to an override function which is run in place of the
original probed function. This means the probed function is not run at all. The replacement function just re‐
turns with the required value.
This helper has security implications, and thus is subject to restrictions. It is only available if the kernel
was compiled with the CONFIG_BPF_KPROBE_OVERRIDE configuration option, and in this case it only works on func‐
tions tagged with ALLOW_ERROR_INJECTION in the kernel code.
Also, the helper is only available for the architectures having the CONFIG_FUNCTION_ERROR_INJECTION option. As
of this writing, x86 architecture is the only one to support this feature.
Return 0
long bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int argval)
Description
Attempt to set the value of the bpf_sock_ops_cb_flags field for the full TCP socket associated to bpf_sock_ops
to argval.
The primary use of this field is to determine if there should be calls to eBPF programs of type
BPF_PROG_TYPE_SOCK_OPS at various points in the TCP code. A program of the same type can change its value, per
connection and as necessary, when the connection is established. This field is directly accessible for read‐
ing, but this helper must be used for updates in order to return an error if an eBPF program tries to set a
callback that is not supported in the current kernel.
argval is a flag array which can combine these flags:
• BPF_SOCK_OPS_RTO_CB_FLAG (retransmission time out)
• BPF_SOCK_OPS_RETRANS_CB_FLAG (retransmission)
• BPF_SOCK_OPS_STATE_CB_FLAG (TCP state change)
• BPF_SOCK_OPS_RTT_CB_FLAG (every RTT)
Therefore, this function can be used to clear a callback flag by setting the appropriate bit to zero. e.g. to
disable the RTO callback:
bpf_sock_ops_cb_flags_set(bpf_sock,
bpf_sock->bpf_sock_ops_cb_flags & ~BPF_SOCK_OPS_RTO_CB_FLAG)
Here are some examples of where one could call such eBPF program:
• When RTO fires.
• When a packet is retransmitted.
• When the connection terminates.
• When a packet is sent.
• When a packet is received.
Return Code -EINVAL if the socket is not a full TCP socket; otherwise, a positive number containing the bits that
could not be set is returned (which comes down to 0 if all bits were set as required).
long bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map *map, u32 key, u64 flags)
Description
This helper is used in programs implementing policies at the socket level. If the message msg is allowed to
pass (i.e. if the verdict eBPF program returns SK_PASS), redirect it to the socket referenced by map (of type
BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinction (ingress path is selected if the flag is present,
egress path otherwise). This is the only flag supported for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)
Description
For socket policies, apply the verdict of the eBPF program to the next bytes (number of bytes) of message msg.
For example, this helper can be used in the following cases:
• A single sendmsg() or sendfile() system call contains multiple logical messages that the eBPF program is
supposed to read and for which it should apply a verdict.
• An eBPF program only cares to read the first bytes of a msg. If the message has a large payload, then set‐
ting up and calling the eBPF program repeatedly for all bytes, even though the verdict is already known,
would create unnecessary overhead.
When called from within an eBPF program, the helper sets a counter internal to the BPF infrastructure, that is
used to apply the last verdict to the next bytes. If bytes is smaller than the current data being processed
from a sendmsg() or sendfile() system call, the first bytes will be sent and the eBPF program will be re-run
with the pointer for start of data pointing to byte number bytes + 1. If bytes is larger than the current data
being processed, then the eBPF verdict will be applied to multiple sendmsg() or sendfile() calls until bytes
are consumed.
Note that if a socket closes with the internal counter holding a non-zero value, this is not a problem because
data is not being buffered for bytes and is sent as it is received.
Return 0
long bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)
Description
For socket policies, prevent the execution of the verdict eBPF program for message msg until bytes (byte num‐
ber) have been accumulated.
This can be used when one needs a specific number of bytes before a verdict can be assigned, even if the data
spans multiple sendmsg() or sendfile() calls. The extreme case would be a user calling sendmsg() repeatedly
with 1-byte long message segments. Obviously, this is bad for performance, but it is still valid. If the eBPF
program needs bytes bytes to validate a header, this helper can be used to prevent the eBPF program to be
called again until bytes have been accumulated.
Return 0
long bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64 flags)
Description
For socket policies, pull in non-linear data from user space for msg and set pointers msg->data and
msg->data_end to start and end bytes offsets into msg, respectively.
If a program of type BPF_PROG_TYPE_SK_MSG is run on a msg it can only parse data that the (data, data_end)
pointers have already consumed. For sendmsg() hooks this is likely the first scatterlist element. But for
calls relying on the sendpage handler (e.g. sendfile()) this will be the range (0, 0) because the data is
shared with user space and by default the objective is to avoid allowing user space to modify data while (or
after) eBPF verdict is being decided. This helper can be used to pull in data and to set the start and end
pointer to given values. Data will be copied if necessary (i.e. if data was not linear and if start and end
pointers do not point to the same chunk).
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
All values for flags are reserved for future usage, and must be left at zero.
Return 0 on success, or a negative error in case of failure.
long bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, int addr_len)
Description
Bind the socket associated to ctx to the address pointed by addr, of length addr_len. This allows for making
outgoing connection from the desired IP address, which can be useful for example when all processes inside a
cgroup should use one single IP address on a host that has multiple IP configured.
This helper works for IPv4 and IPv6, TCP and UDP sockets. The domain (addr->sa_family) must be AF_INET (or
AF_INET6). It's advised to pass zero port (sin_port or sin6_port) which triggers IP_BIND_ADDRESS_NO_PORT-like
behavior and lets the kernel efficiently pick up an unused port as long as 4-tuple is unique. Passing non-zero
port might lead to degraded performance.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)
Description
Adjust (move) xdp_md->data_end by delta bytes. It is possible to both shrink and grow the packet tail. Shrink
done via delta being a negative integer.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index, struct bpf_xfrm_state *xfrm_state, u32 size, u64 flags)
Description
Retrieve the XFRM state (IP transform framework, see also ip-xfrm(8)) at index in XFRM "security path" for
skb.
The retrieved value is stored in the struct bpf_xfrm_state pointed by xfrm_state and of length size.
All values for flags are reserved for future usage, and must be left at zero.
This helper is available only if the kernel was compiled with CONFIG_XFRM configuration option.
Return 0 on success, or a negative error in case of failure.
long bpf_get_stack(void *ctx, void *buf, u32 size, u64 flags)
Description
Return a user or a kernel stack in bpf program provided buffer. To achieve this, the helper needs ctx, which
is a pointer to the context on which the tracing program is executed. To store the stacktrace, the bpf pro‐
gram provides buf with a nonnegative size.
The last argument, flags, holds the number of stack frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel stack.
BPF_F_USER_BUILD_ID
Collect (build_id, file_offset) instead of ips for user stack, only valid if BPF_F_USER_STACK is also
specified.
file_offset is an offset relative to the beginning of the executable or shared object file backing the
vma which the ip falls in. It is not an offset relative to that object's base address. Accordingly, it
must be adjusted by adding (sh_addr - sh_offset), where sh_{addr,offset} correspond to the executable
section containing file_offset in the object, for comparisons to symbols' st_value to be valid.
bpf_get_stack() can collect up to PERF_MAX_STACK_DEPTH both kernel and user frames, subject to sufficient
large buffer size. Note that this limit can be controlled with the sysctl program, and that it should be manu‐
ally increased in order to profile long user stacks (such as stacks for Java programs). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The non-negative copied buf length equal to or less than size on success, or a negative error in case of fail‐
ure.
long bpf_skb_load_bytes_relative(const void *skb, u32 offset, void *to, u32 len, u32 start_header)
Description
This helper is similar to bpf_skb_load_bytes() in that it provides an easy way to load len bytes from offset
from the packet associated to skb, into the buffer pointed by to. The difference to bpf_skb_load_bytes() is
that a fifth argument start_header exists in order to select a base offset to start from. start_header can be
one of:
BPF_HDR_START_MAC
Base offset to load data from is skb's mac header.
BPF_HDR_START_NET
Base offset to load data from is skb's network header.
In general, "direct packet access" is the preferred method to access packet data, however, this helper is in
particular useful in socket filters where skb->data does not always point to the start of the mac header and
where "direct packet access" is not available.
Return 0 on success, or a negative error in case of failure.
long bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen, u32 flags)
Description
Do FIB lookup in kernel tables using parameters in params. If lookup is successful and result shows packet is
to be forwarded, the neighbor tables are searched for the nexthop. If successful (ie., FIB lookup shows for‐
warding and nexthop is resolved), the nexthop address is returned in ipv4_dst or ipv6_dst based on family,
smac is set to mac address of egress device, dmac is set to nexthop mac address, rt_metric is set to metric
from route (IPv4/IPv6 only), and ifindex is set to the device index of the nexthop from the FIB lookup.
plen argument is the size of the passed in struct. flags argument can be a combination of one or more of the
following values:
BPF_FIB_LOOKUP_DIRECT
Do a direct table lookup vs full lookup using FIB rules.
BPF_FIB_LOOKUP_OUTPUT
Perform lookup from an egress perspective (default is ingress).
ctx is either struct xdp_md for XDP programs or struct sk_buff tc cls_act programs.
Return
• < 0 if any input argument is invalid
• 0 on success (packet is forwarded, nexthop neighbor exists)
• > 0 one of BPF_FIB_LKUP_RET_ codes explaining why the packet is not forwarded or needs assist from full
stack
If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then the MTU was exceeded and output params->mtu_result
contains the MTU.
long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
Description
Add an entry to, or update a sockhash map referencing sockets. The skops is used as a new value for the entry
associated to key. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for key.
If the map has eBPF programs (parser and verdict), those will be inherited by the socket being added. If the
socket is already attached to eBPF programs, this results in an error.
Return 0 on success, or a negative error in case of failure.
long bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map *map, void *key, u64 flags)
Description
This helper is used in programs implementing policies at the socket level. If the message msg is allowed to
pass (i.e. if the verdict eBPF program returns SK_PASS), redirect it to the socket referenced by map (of type
BPF_MAP_TYPE_SOCKHASH) using hash key. Both ingress and egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinction (ingress path is selected if the flag is present,
egress path otherwise). This is the only flag supported for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map, void *key, u64 flags)
Description
This helper is used in programs implementing policies at the skb socket level. If the sk_buff skb is allowed
to pass (i.e. if the verdict eBPF program returns SK_PASS), redirect it to the socket referenced by map (of
type BPF_MAP_TYPE_SOCKHASH) using hash key. Both ingress and egress interfaces can be used for redirection.
The BPF_F_INGRESS value in flags is used to make the distinction (ingress path is selected if the flag is
present, egress otherwise). This is the only flag supported for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len)
Description
Encapsulate the packet associated to skb within a Layer 3 protocol header. This header is provided in the buf‐
fer at address hdr, with len its size in bytes. type indicates the protocol of the header and can be one of:
BPF_LWT_ENCAP_SEG6
IPv6 encapsulation with Segment Routing Header (struct ipv6_sr_hdr). hdr only contains the SRH, the
IPv6 header is computed by the kernel.
BPF_LWT_ENCAP_SEG6_INLINE
Only works if skb contains an IPv6 packet. Insert a Segment Routing Header (struct ipv6_sr_hdr) inside
the IPv6 header.
BPF_LWT_ENCAP_IP
IP encapsulation (GRE/GUE/IPIP/etc). The outer header must be IPv4 or IPv6, followed by zero or more
additional headers, up to LWT_BPF_MAX_HEADROOM total bytes in all prepended headers. Please note that
if skb_is_gso(skb) is true, no more than two headers can be prepended, and the inner header, if
present, should be either GRE or UDP/GUE.
BPF_LWT_ENCAP_SEG6* types can be called by BPF programs of type BPF_PROG_TYPE_LWT_IN; BPF_LWT_ENCAP_IP type
can be called by bpf programs of types BPF_PROG_TYPE_LWT_IN and BPF_PROG_TYPE_LWT_XMIT.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len)
Description
Store len bytes from address from into the packet associated to skb, at offset. Only the flags, tag and TLVs
inside the outermost IPv6 Segment Routing Header can be modified through this helper.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32 delta)
Description
Adjust the size allocated to TLVs in the outermost IPv6 Segment Routing Header contained in the packet associ‐
ated to skb, at position offset by delta bytes. Only offsets after the segments are accepted. delta can be as
well positive (growing) as negative (shrinking).
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param, u32 param_len)
Description
Apply an IPv6 Segment Routing action of type action to the packet associated to skb. Each action takes a pa‐
rameter contained at address param, and of length param_len bytes. action can be one of:
SEG6_LOCAL_ACTION_END_X
End.X action: Endpoint with Layer-3 cross-connect. Type of param: struct in6_addr.
SEG6_LOCAL_ACTION_END_T
End.T action: Endpoint with specific IPv6 table lookup. Type of param: int.
SEG6_LOCAL_ACTION_END_B6
End.B6 action: Endpoint bound to an SRv6 policy. Type of param: struct ipv6_sr_hdr.
SEG6_LOCAL_ACTION_END_B6_ENCAP
End.B6.Encap action: Endpoint bound to an SRv6 encapsulation policy. Type of param: struct
ipv6_sr_hdr.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all
checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper
is used in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_rc_repeat(void *ctx)
Description
This helper is used in programs implementing IR decoding, to report a successfully decoded repeat key message.
This delays the generation of a key up event for previously generated key down event.
Some IR protocols like NEC have a special IR message for repeating last button, for when a button is held
down.
The ctx should point to the lirc sample as passed into the program.
This helper is only available is the kernel was compiled with the CONFIG_BPF_LIRC_MODE2 configuration option
set to "y".
Return 0
long bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)
Description
This helper is used in programs implementing IR decoding, to report a successfully decoded key press with
scancode, toggle value in the given protocol. The scancode will be translated to a keycode using the rc
keymap, and reported as an input key down event. After a period a key up event is generated. This period can
be extended by calling either bpf_rc_keydown() again with the same values, or calling bpf_rc_repeat().
Some protocols include a toggle bit, in case the button was released and pressed again between consecutive
scancodes.
The ctx should point to the lirc sample as passed into the program.
The protocol is the decoded protocol number (see enum rc_proto for some predefined values).
This helper is only available is the kernel was compiled with the CONFIG_BPF_LIRC_MODE2 configuration option
set to "y".
Return 0
u64 bpf_skb_cgroup_id(struct sk_buff *skb)
Description
Return the cgroup v2 id of the socket associated with the skb. This is roughly similar to the
bpf_get_cgroup_classid() helper for cgroup v1 by providing a tag resp. identifier that can be matched on or
used for map lookups e.g. to implement policy. The cgroup v2 id of a given path in the hierarchy is exposed in
user space through the f_handle API in order to get to the same 64-bit id.
This helper can be used on TC egress path, but not on ingress, and is available only if the kernel was com‐
piled with the CONFIG_SOCK_CGROUP_DATA configuration option.
Return The id is returned or 0 in case the id could not be retrieved.
u64 bpf_get_current_cgroup_id(void)
Description
Get the current cgroup id based on the cgroup within which the current task is running.
Return A 64-bit integer containing the current cgroup id based on the cgroup within which the current task is run‐
ning.
void *bpf_get_local_storage(void *map, u64 flags)
Description
Get the pointer to the local storage area. The type and the size of the local storage is defined by the map
argument. The flags meaning is specific for each map type, and has to be 0 for cgroup local storage.
Depending on the BPF program type, a local storage area can be shared between multiple instances of the BPF
program, running simultaneously.
A user should care about the synchronization by himself. For example, by using the BPF_ATOMIC instructions to
alter the shared data.
Return A pointer to the local storage area.
long bpf_sk_select_reuseport(struct sk_reuseport_md *reuse, struct bpf_map *map, void *key, u64 flags)
Description
Select a SO_REUSEPORT socket from a BPF_MAP_TYPE_REUSEPORT_SOCKARRAY map. It checks the selected socket is
matching the incoming request in the socket buffer.
Return 0 on success, or a negative error in case of failure.
u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int ancestor_level)
Description
Return id of cgroup v2 that is ancestor of cgroup associated with the skb at the ancestor_level. The root
cgroup is at ancestor_level zero and each step down the hierarchy increments the level. If ancestor_level ==
level of cgroup associated with skb, then return value will be same as that of bpf_skb_cgroup_id().
The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup
associated with skb.
The format of returned id and helper limitations are same as in bpf_skb_cgroup_id().
Return The id is returned or 0 in case the id could not be retrieved.
struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
Description
Look for TCP socket matching tuple, optionally in a child network namespace netns. The return value must be
checked, and if non-NULL, released via bpf_sk_release().
The ctx should point to the context of the program, such as the skb or socket (depending on the hook in use).
This is used to determine the base network namespace for the lookup.
tuple_size must be one of:
sizeof(tuple->ipv4)
Look for an IPv4 socket.
sizeof(tuple->ipv6)
Look for an IPv6 socket.
If the netns is a negative signed 32-bit integer, then the socket lookup table in the netns associated with
the ctx will be used. For the TC hooks, this is the netns of the device in the skb. For socket hooks, this is
the netns of the socket. If netns is any other signed 32-bit value greater than or equal to zero then it
specifies the ID of the netns relative to the netns associated with the ctx. netns values beyond the range of
32-bit integers are reserved for future use.
All values for flags are reserved for future usage, and must be left at zero.
This helper is available only if the kernel was compiled with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure. For sockets with reuseport option, the struct
bpf_sock result is from reuse->socks[] using the hash of the tuple.
struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
Description
Look for UDP socket matching tuple, optionally in a child network namespace netns. The return value must be
checked, and if non-NULL, released via bpf_sk_release().
The ctx should point to the context of the program, such as the skb or socket (depending on the hook in use).
This is used to determine the base network namespace for the lookup.
tuple_size must be one of:
sizeof(tuple->ipv4)
Look for an IPv4 socket.
sizeof(tuple->ipv6)
Look for an IPv6 socket.
If the netns is a negative signed 32-bit integer, then the socket lookup table in the netns associated with
the ctx will be used. For the TC hooks, this is the netns of the device in the skb. For socket hooks, this is
the netns of the socket. If netns is any other signed 32-bit value greater than or equal to zero then it
specifies the ID of the netns relative to the netns associated with the ctx. netns values beyond the range of
32-bit integers are reserved for future use.
All values for flags are reserved for future usage, and must be left at zero.
This helper is available only if the kernel was compiled with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure. For sockets with reuseport option, the struct
bpf_sock result is from reuse->socks[] using the hash of the tuple.
long bpf_sk_release(void *sock)
Description
Release the reference held by sock. sock must be a non-NULL pointer that was returned from
bpf_sk_lookup_xxx().
Return 0 on success, or a negative error in case of failure.
long bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
Description
Push an element value in map. flags is one of:
BPF_EXIST
If the queue/stack is full, the oldest element is removed to make room for this.
Return 0 on success, or a negative error in case of failure.
long bpf_map_pop_elem(struct bpf_map *map, void *value)
Description
Pop an element from map.
Return 0 on success, or a negative error in case of failure.
long bpf_map_peek_elem(struct bpf_map *map, void *value)
Description
Get an element from map without removing it.
Return 0 on success, or a negative error in case of failure.
long bpf_msg_push_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)
Description
For socket policies, insert len bytes into msg at offset start.
If a program of type BPF_PROG_TYPE_SK_MSG is run on a msg it may want to insert metadata or options into the
msg. This can later be read and used by any of the lower layer BPF hooks.
This helper may fail if under memory pressure (a malloc fails) in these cases BPF programs will get an appro‐
priate error and BPF programs will need to handle them.
Return 0 on success, or a negative error in case of failure.
long bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)
Description
Will remove len bytes from a msg starting at byte start. This may result in ENOMEM errors under certain situ‐
ations if an allocation and copy are required due to a full ring buffer. However, the helper will try to
avoid doing the allocation if possible. Other errors can occur if input parameters are invalid either due to
start byte not being valid part of msg payload and/or pop value being to large.
Return 0 on success, or a negative error in case of failure.
long bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)
Description
This helper is used in programs implementing IR decoding, to report a successfully decoded pointer movement.
The ctx should point to the lirc sample as passed into the program.
This helper is only available is the kernel was compiled with the CONFIG_BPF_LIRC_MODE2 configuration option
set to "y".
Return 0
long bpf_spin_lock(struct bpf_spin_lock *lock)
Description
Acquire a spinlock represented by the pointer lock, which is stored as part of a value of a map. Taking the
lock allows to safely update the rest of the fields in that value. The spinlock can (and must) later be re‐
leased with a call to bpf_spin_unlock(lock).
Spinlocks in BPF programs come with a number of restrictions and constraints:
• bpf_spin_lock objects are only allowed inside maps of types BPF_MAP_TYPE_HASH and BPF_MAP_TYPE_ARRAY (this
list could be extended in the future).
• BTF description of the map is mandatory.
• The BPF program can take ONE lock at a time, since taking two or more could cause dead locks.
• Only one struct bpf_spin_lock is allowed per map element.
• When the lock is taken, calls (either BPF to BPF or helpers) are not allowed.
• The BPF_LD_ABS and BPF_LD_IND instructions are not allowed inside a spinlock-ed region.
• The BPF program MUST call bpf_spin_unlock() to release the lock, on all execution paths, before it returns.
• The BPF program can access struct bpf_spin_lock only via the bpf_spin_lock() and bpf_spin_unlock() helpers.
Loading or storing data into the struct bpf_spin_lock lock; field of a map is not allowed.
• To use the bpf_spin_lock() helper, the BTF description of the map value must be a struct and have struct
bpf_spin_lock anyname; field at the top level. Nested lock inside another struct is not allowed.
• The struct bpf_spin_lock lock field in a map value must be aligned on a multiple of 4 bytes in that value.
• Syscall with command BPF_MAP_LOOKUP_ELEM does not copy the bpf_spin_lock field to user space.
• Syscall with command BPF_MAP_UPDATE_ELEM, or update from a BPF program, do not update the bpf_spin_lock
field.
• bpf_spin_lock cannot be on the stack or inside a networking packet (it can only be inside of a map values).
• bpf_spin_lock is available to root only.
• Tracing programs and socket filter programs cannot use bpf_spin_lock() due to insufficient preemption checks
(but this may change in the future).
• bpf_spin_lock is not allowed in inner maps of map-in-map.
Return 0
long bpf_spin_unlock(struct bpf_spin_lock *lock)
Description
Release the lock previously locked by a call to bpf_spin_lock(lock).
Return 0
struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)
Description
This helper gets a struct bpf_sock pointer such that all the fields in this bpf_sock can be accessed.
Return A struct bpf_sock pointer on success, or NULL in case of failure.
struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk)
Description
This helper gets a struct bpf_tcp_sock pointer from a struct bpf_sock pointer.
Return A struct bpf_tcp_sock pointer on success, or NULL in case of failure.
long bpf_skb_ecn_set_ce(struct sk_buff *skb)
Description
Set ECN (Explicit Congestion Notification) field of IP header to CE (Congestion Encountered) if current value
is ECT (ECN Capable Transport). Otherwise, do nothing. Works with IPv6 and IPv4.
Return 1 if the CE flag is set (either by the current helper call or because it was already present), 0 if it is not
set.
struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)
Description
Return a struct bpf_sock pointer in TCP_LISTEN state. bpf_sk_release() is unnecessary and not allowed.
Return A struct bpf_sock pointer on success, or NULL in case of failure.
struct bpf_sock *bpf_skc_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
Description
Look for TCP socket matching tuple, optionally in a child network namespace netns. The return value must be
checked, and if non-NULL, released via bpf_sk_release().
This function is identical to bpf_sk_lookup_tcp(), except that it also returns timewait or request sockets.
Use bpf_sk_fullsock() or bpf_tcp_sock() to access the full structure.
This helper is available only if the kernel was compiled with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure. For sockets with reuseport option, the struct
bpf_sock result is from reuse->socks[] using the hash of the tuple.
long bpf_tcp_check_syncookie(void *sk, void *iph, u32 iph_len, struct tcphdr *th, u32 th_len)
Description
Check whether iph and th contain a valid SYN cookie ACK for the listening socket in sk.
iph points to the start of the IPv4 or IPv6 header, while iph_len contains sizeof(struct iphdr) or
sizeof(struct ipv6hdr).
th points to the start of the TCP header, while th_len contains the length of the TCP header (at least
sizeof(struct tcphdr)).
Return 0 if iph and th are a valid SYN cookie ACK, or a negative error otherwise.
long bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf, size_t buf_len, u64 flags)
Description
Get name of sysctl in /proc/sys/ and copy it into provided by program buffer buf of size buf_len.
The buffer is always NUL terminated, unless it's zero-sized.
If flags is zero, full name (e.g. "net/ipv4/tcp_mem") is copied. Use BPF_F_SYSCTL_BASE_NAME flag to copy base
name only (e.g. "tcp_mem").
Return Number of character copied (not including the trailing NUL).
-E2BIG if the buffer wasn't big enough (buf will contain truncated name in this case).
long bpf_sysctl_get_current_value(struct bpf_sysctl *ctx, char *buf, size_t buf_len)
Description
Get current value of sysctl as it is presented in /proc/sys (incl. newline, etc), and copy it as a string into
provided by program buffer buf of size buf_len.
The whole value is copied, no matter what file position user space issued e.g. sys_read at.
The buffer is always NUL terminated, unless it's zero-sized.
Return Number of character copied (not including the trailing NUL).
-E2BIG if the buffer wasn't big enough (buf will contain truncated name in this case).
-EINVAL if current value was unavailable, e.g. because sysctl is uninitialized and read returns -EIO for it.
long bpf_sysctl_get_new_value(struct bpf_sysctl *ctx, char *buf, size_t buf_len)
Description
Get new value being written by user space to sysctl (before the actual write happens) and copy it as a string
into provided by program buffer buf of size buf_len.
User space may write new value at file position > 0.
The buffer is always NUL terminated, unless it's zero-sized.
Return Number of character copied (not including the trailing NUL).
-E2BIG if the buffer wasn't big enough (buf will contain truncated name in this case).
-EINVAL if sysctl is being read.
long bpf_sysctl_set_new_value(struct bpf_sysctl *ctx, const char *buf, size_t buf_len)
Description
Override new value being written by user space to sysctl with value provided by program in buffer buf of size
buf_len.
buf should contain a string in same form as provided by user space on sysctl write.
User space may write new value at file position > 0. To override the whole sysctl value file position should
be set to zero.
Return 0 on success.
-E2BIG if the buf_len is too big.
-EINVAL if sysctl is being read.
long bpf_strtol(const char *buf, size_t buf_len, u64 flags, long *res)
Description
Convert the initial part of the string from buffer buf of size buf_len to a long integer according to the
given base and save the result in res.
The string may begin with an arbitrary amount of white space (as determined by isspace(3)) followed by a sin‐
gle optional '-' sign.
Five least significant bits of flags encode base, other bits are currently unused.
Base must be either 8, 10, 16 or 0 to detect it automatically similar to user space strtol(3).
Return Number of characters consumed on success. Must be positive but no more than buf_len.
-EINVAL if no valid digits were found or unsupported base was provided.
-ERANGE if resulting value was out of range.
long bpf_strtoul(const char *buf, size_t buf_len, u64 flags, unsigned long *res)
Description
Convert the initial part of the string from buffer buf of size buf_len to an unsigned long integer according
to the given base and save the result in res.
The string may begin with an arbitrary amount of white space (as determined by isspace(3)).
Five least significant bits of flags encode base, other bits are currently unused.
Base must be either 8, 10, 16 or 0 to detect it automatically similar to user space strtoul(3).
Return Number of characters consumed on success. Must be positive but no more than buf_len.
-EINVAL if no valid digits were found or unsupported base was provided.
-ERANGE if resulting value was out of range.
void *bpf_sk_storage_get(struct bpf_map *map, void *sk, void *value, u64 flags)
Description
Get a bpf-local-storage from a sk.
Logically, it could be thought of getting the value from a map with sk as the key. From this perspective,
the usage is not much different from bpf_map_lookup_elem(map, &sk) except this helper enforces the key must be
a full socket and the map must be a BPF_MAP_TYPE_SK_STORAGE also.
Underneath, the value is stored locally at sk instead of the map. The map is used as the bpf-local-storage
"type". The bpf-local-storage "type" (i.e. the map) is searched against all bpf-local-storages residing at sk.
sk is a kernel struct sock pointer for LSM program. sk is a struct bpf_sock pointer for other program types.
An optional flags (BPF_SK_STORAGE_GET_F_CREATE) can be used such that a new bpf-local-storage will be created
if one does not exist. value can be used together with BPF_SK_STORAGE_GET_F_CREATE to specify the initial
value of a bpf-local-storage. If value is NULL, the new bpf-local-storage will be zero initialized.
Return A bpf-local-storage pointer is returned on success.
NULL if not found or there was an error in adding a new bpf-local-storage.
long bpf_sk_storage_delete(struct bpf_map *map, void *sk)
Description
Delete a bpf-local-storage from a sk.
Return 0 on success.
-ENOENT if the bpf-local-storage cannot be found. -EINVAL if sk is not a fullsock (e.g. a request_sock).
long bpf_send_signal(u32 sig)
Description
Send signal sig to the process of the current task. The signal may be delivered to any of this process's
threads.
Return 0 on success or successfully queued.
-EBUSY if work queue under nmi is full.
-EINVAL if sig is invalid.
-EPERM if no permission to send the sig.
-EAGAIN if bpf program can try again.
s64 bpf_tcp_gen_syncookie(void *sk, void *iph, u32 iph_len, struct tcphdr *th, u32 th_len)
Description
Try to issue a SYN cookie for the packet with corresponding IP/TCP headers, iph and th, on the listening
socket in sk.
iph points to the start of the IPv4 or IPv6 header, while iph_len contains sizeof(struct iphdr) or
sizeof(struct ipv6hdr).
th points to the start of the TCP header, while th_len contains the length of the TCP header with options (at
least sizeof(struct tcphdr)).
Return On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for
that cookie, and the top 16 bits are unused.
On failure, the returned value is one of the following:
-EINVAL SYN cookie cannot be issued due to error
-ENOENT SYN cookie should not be issued (no SYN flood)
-EOPNOTSUPP kernel configuration does not enable SYN cookies
-EPROTONOSUPPORT IP packet version is not 4 or 6
long bpf_skb_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)
Description
Write raw data blob into a special BPF perf event held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes: PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type, and
PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for which the value must be put, masked with BPF_F_INDEX_MASK.
Alternatively, flags can be set to BPF_F_CURRENT_CPU to indicate that the index of the current CPU core should
be used.
The value to write, of size, is passed through eBPF stack and pointed by data.
ctx is a pointer to in-kernel struct sk_buff.
This helper is similar to bpf_perf_event_output() but restricted to raw_tracepoint bpf programs.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_user(void *dst, u32 size, const void *unsafe_ptr)
Description
Safely attempt to read size bytes from user space address unsafe_ptr and store the data in dst.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
Description
Safely attempt to read size bytes from kernel space address unsafe_ptr and store the data in dst.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_user_str(void *dst, u32 size, const void *unsafe_ptr)
Description
Copy a NUL terminated string from an unsafe user address unsafe_ptr to dst. The size should include the termi‐
nating NUL byte. In case the string length is smaller than size, the target is not padded with further NUL
bytes. If the string length is larger than size, just size-1 bytes are copied and the last byte is set to NUL.
On success, returns the number of bytes that were written, including the terminal NUL. This makes this helper
useful in tracing programs for reading strings, and more importantly to get its length at runtime. See the
following snippet:
SEC("kprobe/sys_open")
void bpf_sys_open(struct pt_regs *ctx)
{
char buf[PATHLEN]; // PATHLEN is defined to 256
int res = bpf_probe_read_user_str(buf, sizeof(buf),
ctx->di);
// Consume buf, for example push it to
// userspace via bpf_perf_event_output(); we
// can use res (the string length) as event
// size, after checking its boundaries.
}
In comparison, using bpf_probe_read_user() helper here instead to read the string would require to estimate
the length at compile time, and would often result in copying more memory than necessary.
Another useful use case is when parsing individual process arguments or individual environment variables navi‐
gating current->mm->arg_start and current->mm->env_start: using this helper and the return value, one can
quickly iterate at the right offset of the memory area.
Return On success, the strictly positive length of the output string, including the trailing NUL character. On error,
a negative value.
long bpf_probe_read_kernel_str(void *dst, u32 size, const void *unsafe_ptr)
Description
Copy a NUL terminated string from an unsafe kernel address unsafe_ptr to dst. Same semantics as with
bpf_probe_read_user_str() apply.
Return On success, the strictly positive length of the string, including the trailing NUL character. On error, a neg‐
ative value.
long bpf_tcp_send_ack(void *tp, u32 rcv_nxt)
Description
Send out a tcp-ack. tp is the in-kernel struct tcp_sock. rcv_nxt is the ack_seq to be sent out.
Return 0 on success, or a negative error in case of failure.
long bpf_send_signal_thread(u32 sig)
Description
Send signal sig to the thread corresponding to the current task.
Return 0 on success or successfully queued.
-EBUSY if work queue under nmi is full.
-EINVAL if sig is invalid.
-EPERM if no permission to send the sig.
-EAGAIN if bpf program can try again.
u64 bpf_jiffies64(void)
Description
Obtain the 64bit jiffies
Return The 64 bit jiffies
long bpf_read_branch_records(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 flags)
Description
For an eBPF program attached to a perf event, retrieve the branch records (struct perf_branch_entry) associ‐
ated to ctx and store it in the buffer pointed by buf up to size size bytes.
Return On success, number of bytes written to buf. On error, a negative value.
The flags can be set to BPF_F_GET_BRANCH_RECORDS_SIZE to instead return the number of bytes required to store
all the branch entries. If this flag is set, buf may be NULL.
-EINVAL if arguments invalid or size not a multiple of sizeof(struct perf_branch_entry).
-ENOENT if architecture does not support branch records.
long bpf_get_ns_current_pid_tgid(u64 dev, u64 ino, struct bpf_pidns_info *nsdata, u32 size)
Description
Returns 0 on success, values for pid and tgid as seen from the current namespace will be returned in nsdata.
Return 0 on success, or one of the following in case of failure:
-EINVAL if dev and inum supplied don't match dev_t and inode number with nsfs of current task, or if dev con‐
version to dev_t lost high bits.
-ENOENT if pidns does not exists for the current task.
long bpf_xdp_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)
Description
Write raw data blob into a special BPF perf event held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes: PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type, and
PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for which the value must be put, masked with BPF_F_INDEX_MASK.
Alternatively, flags can be set to BPF_F_CURRENT_CPU to indicate that the index of the current CPU core should
be used.
The value to write, of size, is passed through eBPF stack and pointed by data.
ctx is a pointer to in-kernel struct xdp_buff.
This helper is similar to bpf_perf_eventoutput() but restricted to raw_tracepoint bpf programs.
Return 0 on success, or a negative error in case of failure.
u64 bpf_get_netns_cookie(void *ctx)
Description
Retrieve the cookie (generated by the kernel) of the network namespace the input ctx is associated with. The
network namespace cookie remains stable for its lifetime and provides a global identifier that can be assumed
unique. If ctx is NULL, then the helper returns the cookie for the initial network namespace. The cookie it‐
self is very similar to that of bpf_get_socket_cookie() helper, but for network namespaces instead of sockets.
Return A 8-byte long opaque number.
u64 bpf_get_current_ancestor_cgroup_id(int ancestor_level)
Description
Return id of cgroup v2 that is ancestor of the cgroup associated with the current task at the ancestor_level.
The root cgroup is at ancestor_level zero and each step down the hierarchy increments the level. If ances‐
tor_level == level of cgroup associated with the current task, then return value will be the same as that of
bpf_get_current_cgroup_id().
The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup
associated with the current task.
The format of returned id and helper limitations are same as in bpf_get_current_cgroup_id().
Return The id is returned or 0 in case the id could not be retrieved.
long bpf_sk_assign(struct sk_buff *skb, void *sk, u64 flags)
Description
Helper is overloaded depending on BPF program type. This description applies to BPF_PROG_TYPE_SCHED_CLS and
BPF_PROG_TYPE_SCHED_ACT programs.
Assign the sk to the skb. When combined with appropriate routing configuration to receive the packet towards
the socket, will cause skb to be delivered to the specified socket. Subsequent redirection of skb via
bpf_redirect(), bpf_clone_redirect() or other methods outside of BPF may interfere with successful delivery to
the socket.
This operation is only valid from TC ingress path.
The flags argument must be zero.
Return 0 on success, or a negative error in case of failure:
-EINVAL if specified flags are not supported.
-ENOENT if the socket is unavailable for assignment.
-ENETUNREACH if the socket is unreachable (wrong netns).
-EOPNOTSUPP if the operation is not supported, for example a call from outside of TC ingress.
-ESOCKTNOSUPPORT if the socket type is not supported (reuseport).
long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64 flags)
Description
Helper is overloaded depending on BPF program type. This description applies to BPF_PROG_TYPE_SK_LOOKUP pro‐
grams.
Select the sk as a result of a socket lookup.
For the operation to succeed passed socket must be compatible with the packet description provided by the ctx
object.
L4 protocol (IPPROTO_TCP or IPPROTO_UDP) must be an exact match. While IP family (AF_INET or AF_INET6) must be
compatible, that is IPv6 sockets that are not v6-only can be selected for IPv4 packets.
Only TCP listeners and UDP unconnected sockets can be selected. sk can also be NULL to reset any previous se‐
lection.
flags argument can combination of following values:
• BPF_SK_LOOKUP_F_REPLACE to override the previous socket selection, potentially done by a BPF program that
ran before us.
• BPF_SK_LOOKUP_F_NO_REUSEPORT to skip load-balancing within reuseport group for the socket being selected.
On success ctx->sk will point to the selected socket.
Return 0 on success, or a negative errno in case of failure.
• -EAFNOSUPPORT if socket family (sk->family) is not compatible with packet family (ctx->family).
• -EEXIST if socket has been already selected, potentially by another program, and BPF_SK_LOOKUP_F_REPLACE
flag was not specified.
• -EINVAL if unsupported flags were specified.
• -EPROTOTYPE if socket L4 protocol (sk->protocol) doesn't match packet protocol (ctx->protocol).
• -ESOCKTNOSUPPORT if socket is not in allowed state (TCP listening or UDP unconnected).
u64 bpf_ktime_get_boot_ns(void)
Description
Return the time elapsed since system boot, in nanoseconds. Does include the time the system was suspended.
See: clock_gettime(CLOCK_BOOTTIME)
Return Current ktime.
long bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size, const void *data, u32 data_len)
Description
bpf_seq_printf() uses seq_file seq_printf() to print out the format string. The m represents the seq_file.
The fmt and fmt_size are for the format string itself. The data and data_len are format string arguments. The
data are a u64 array and corresponding format string values are stored in the array. For strings and pointers
where pointees are accessed, only the pointer values are stored in the data array. The data_len is the size
of data in bytes - must be a multiple of 8.
Formats %s, %p{i,I}{4,6} requires to read kernel memory. Reading kernel memory may fail due to either invalid
address or valid address but requiring a major memory fault. If reading kernel memory fails, the string for %s
will be an empty string, and the ip address for %p{i,I}{4,6} will be 0. Not returning error to bpf program is
consistent with what bpf_trace_printk() does for now.
Return 0 on success, or a negative error in case of failure:
-EBUSY if per-CPU memory copy buffer is busy, can try again by returning 1 from bpf program.
-EINVAL if arguments are invalid, or if fmt is invalid/unsupported.
-E2BIG if fmt contains too many format specifiers.
-EOVERFLOW if an overflow happened: The same object will be tried again.
long bpf_seq_write(struct seq_file *m, const void *data, u32 len)
Description
bpf_seq_write() uses seq_file seq_write() to write the data. The m represents the seq_file. The data and len
represent the data to write in bytes.
Return 0 on success, or a negative error in case of failure:
-EOVERFLOW if an overflow happened: The same object will be tried again.
u64 bpf_sk_cgroup_id(void *sk)
Description
Return the cgroup v2 id of the socket sk.
sk must be a non-NULL pointer to a socket, e.g. one returned from bpf_sk_lookup_xxx(), bpf_sk_fullsock(), etc.
The format of returned id is same as in bpf_skb_cgroup_id().
This helper is available only if the kernel was compiled with the CONFIG_SOCK_CGROUP_DATA configuration op‐
tion.
Return The id is returned or 0 in case the id could not be retrieved.
u64 bpf_sk_ancestor_cgroup_id(void *sk, int ancestor_level)
Description
Return id of cgroup v2 that is ancestor of cgroup associated with the sk at the ancestor_level. The root
cgroup is at ancestor_level zero and each step down the hierarchy increments the level. If ancestor_level ==
level of cgroup associated with sk, then return value will be same as that of bpf_sk_cgroup_id().
The helper is useful to implement policies based on cgroups that are upper in hierarchy than immediate cgroup
associated with sk.
The format of returned id and helper limitations are same as in bpf_sk_cgroup_id().
Return The id is returned or 0 in case the id could not be retrieved.
long bpf_ringbuf_output(void *ringbuf, void *data, u64 size, u64 flags)
Description
Copy size bytes from data into a ring buffer ringbuf. If BPF_RB_NO_WAKEUP is specified in flags, no notifica‐
tion of new data availability is sent. If BPF_RB_FORCE_WAKEUP is specified in flags, notification of new data
availability is sent unconditionally. If 0 is specified in flags, an adaptive notification of new data avail‐
ability is sent.
An adaptive notification is a notification sent whenever the user-space process has caught up and consumed all
available payloads. In case the user-space process is still processing a previous payload, then no notifica‐
tion is needed as it will process the newly added payload automatically.
Return 0 on success, or a negative error in case of failure.
void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)
Description
Reserve size bytes of payload in a ring buffer ringbuf. flags must be 0.
Return Valid pointer with size bytes of memory available; NULL, otherwise.
void bpf_ringbuf_submit(void *data, u64 flags)
Description
Submit reserved ring buffer sample, pointed to by data. If BPF_RB_NO_WAKEUP is specified in flags, no notifi‐
cation of new data availability is sent. If BPF_RB_FORCE_WAKEUP is specified in flags, notification of new
data availability is sent unconditionally. If 0 is specified in flags, an adaptive notification of new data
availability is sent.
See 'bpf_ringbuf_output()' for the definition of adaptive notification.
Return Nothing. Always succeeds.
void bpf_ringbuf_discard(void *data, u64 flags)
Description
Discard reserved ring buffer sample, pointed to by data. If BPF_RB_NO_WAKEUP is specified in flags, no noti‐
fication of new data availability is sent. If BPF_RB_FORCE_WAKEUP is specified in flags, notification of new
data availability is sent unconditionally. If 0 is specified in flags, an adaptive notification of new data
availability is sent.
See 'bpf_ringbuf_output()' for the definition of adaptive notification.
Return Nothing. Always succeeds.
u64 bpf_ringbuf_query(void *ringbuf, u64 flags)
Description
Query various characteristics of provided ring buffer. What exactly is queries is determined by flags:
• BPF_RB_AVAIL_DATA: Amount of data not yet consumed.
• BPF_RB_RING_SIZE: The size of ring buffer.
• BPF_RB_CONS_POS: Consumer position (can wrap around).
• BPF_RB_PROD_POS: Producer(s) position (can wrap around).
Data returned is just a momentary snapshot of actual values and could be inaccurate, so this facility should
be used to power heuristics and for reporting, not to make 100% correct calculation.
Return Requested value, or 0, if flags are not recognized.
long bpf_csum_level(struct sk_buff *skb, u64 level)
Description
Change the skbs checksum level by one layer up or down, or reset it entirely to none in order to have the
stack perform checksum validation. The level is applicable to the following protocols: TCP, UDP, GRE, SCTP,
FCOE. For example, a decap of | ETH | IP | UDP | GUE | IP | TCP | into | ETH | IP | TCP | through bpf_skb_ad‐
just_room() helper with passing in BPF_F_ADJ_ROOM_NO_CSUM_RESET flag would require one call to
bpf_csum_level() with BPF_CSUM_LEVEL_DEC since the UDP header is removed. Similarly, an encap of the latter
into the former could be accompanied by a helper call to bpf_csum_level() with BPF_CSUM_LEVEL_INC if the skb
is still intended to be processed in higher layers of the stack instead of just egressing at tc.
There are three supported level settings at this time:
• BPF_CSUM_LEVEL_INC: Increases skb->csum_level for skbs with CHECKSUM_UNNECESSARY.
• BPF_CSUM_LEVEL_DEC: Decreases skb->csum_level for skbs with CHECKSUM_UNNECESSARY.
• BPF_CSUM_LEVEL_RESET: Resets skb->csum_level to 0 and sets CHECKSUM_NONE to force checksum validation by the
stack.
• BPF_CSUM_LEVEL_QUERY: No-op, returns the current skb->csum_level.
Return 0 on success, or a negative error in case of failure. In the case of BPF_CSUM_LEVEL_QUERY, the current
skb->csum_level is returned or the error code -EACCES in case the skb is not subject to CHECKSUM_UNNECESSARY.
struct tcp6_sock *bpf_skc_to_tcp6_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp6_sock pointer.
Return sk if casting is valid, or NULL otherwise.
struct tcp_sock *bpf_skc_to_tcp_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp_sock pointer.
Return sk if casting is valid, or NULL otherwise.
struct tcp_timewait_sock *bpf_skc_to_tcp_timewait_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp_timewait_sock pointer.
Return sk if casting is valid, or NULL otherwise.
struct tcp_request_sock *bpf_skc_to_tcp_request_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp_request_sock pointer.
Return sk if casting is valid, or NULL otherwise.
struct udp6_sock *bpf_skc_to_udp6_sock(void *sk)
Description
Dynamically cast a sk pointer to a udp6_sock pointer.
Return sk if casting is valid, or NULL otherwise.
long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)
Description
Return a user or a kernel stack in bpf program provided buffer. To achieve this, the helper needs task, which
is a valid pointer to struct task_struct. To store the stacktrace, the bpf program provides buf with a nonneg‐
ative size.
The last argument, flags, holds the number of stack frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel stack.
BPF_F_USER_BUILD_ID
Collect buildid+offset instead of ips for user stack, only valid if BPF_F_USER_STACK is also specified.
bpf_get_task_stack() can collect up to PERF_MAX_STACK_DEPTH both kernel and user frames, subject to sufficient
large buffer size. Note that this limit can be controlled with the sysctl program, and that it should be manu‐
ally increased in order to profile long user stacks (such as stacks for Java programs). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The non-negative copied buf length equal to or less than size on success, or a negative error in case of fail‐
ure.
long bpf_load_hdr_opt(struct bpf_sock_ops *skops, void *searchby_res, u32 len, u64 flags)
Description
Load header option. Support reading a particular TCP header option for bpf program (BPF_PROG_TYPE_SOCK_OPS).
If flags is 0, it will search the option from the skops->skb_data. The comment in struct bpf_sock_ops has de‐
tails on what skb_data contains under different skops->op.
The first byte of the searchby_res specifies the kind that it wants to search.
If the searching kind is an experimental kind (i.e. 253 or 254 according to RFC6994). It also needs to spec‐
ify the "magic" which is either 2 bytes or 4 bytes. It then also needs to specify the size of the magic by
using the 2nd byte which is "kind-length" of a TCP header option and the "kind-length" also includes the first
2 bytes "kind" and "kind-length" itself as a normal TCP header option also does.
For example, to search experimental kind 254 with 2 byte magic 0xeB9F, the searchby_res should be [ 254, 4,
0xeB, 0x9F, 0, 0, .... 0 ].
To search for the standard window scale option (3), the searchby_res should be [ 3, 0, 0, .... 0 ]. Note,
kind-length must be 0 for regular option.
Searching for No-Op (0) and End-of-Option-List (1) are not supported.
len must be at least 2 bytes which is the minimal size of a header option.
Supported flags:
• BPF_LOAD_HDR_OPT_TCP_SYN to search from the saved_syn packet or the just-received syn packet.
Return > 0 when found, the header option is copied to searchby_res. The return value is the total length copied. On
failure, a negative error code is returned:
-EINVAL if a parameter is invalid.
-ENOMSG if the option is not found.
-ENOENT if no syn packet is available when BPF_LOAD_HDR_OPT_TCP_SYN is used.
-ENOSPC if there is not enough space. Only len number of bytes are copied.
-EFAULT on failure to parse the header options in the packet.
-EPERM if the helper cannot be used under the current skops->op.
long bpf_store_hdr_opt(struct bpf_sock_ops *skops, const void *from, u32 len, u64 flags)
Description
Store header option. The data will be copied from buffer from with length len to the TCP header.
The buffer from should have the whole option that includes the kind, kind-length, and the actual option data.
The len must be at least kind-length long. The kind-length does not have to be 4 byte aligned. The kernel
will take care of the padding and setting the 4 bytes aligned value to th->doff.
This helper will check for duplicated option by searching the same option in the outgoing skb.
This helper can only be called during BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
Return 0 on success, or negative error in case of failure:
-EINVAL If param is invalid.
-ENOSPC if there is not enough space in the header. Nothing has been written
-EEXIST if the option already exists.
-EFAULT on failure to parse the existing header options.
-EPERM if the helper cannot be used under the current skops->op.
long bpf_reserve_hdr_opt(struct bpf_sock_ops *skops, u32 len, u64 flags)
Description
Reserve len bytes for the bpf header option. The space will be used by bpf_store_hdr_opt() later in
BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
If bpf_reserve_hdr_opt() is called multiple times, the total number of bytes will be reserved.
This helper can only be called during BPF_SOCK_OPS_HDR_OPT_LEN_CB.
Return 0 on success, or negative error in case of failure:
-EINVAL if a parameter is invalid.
-ENOSPC if there is not enough space in the header.
-EPERM if the helper cannot be used under the current skops->op.
void *bpf_inode_storage_get(struct bpf_map *map, void *inode, void *value, u64 flags)
Description
Get a bpf_local_storage from an inode.
Logically, it could be thought of as getting the value from a map with inode as the key. From this perspec‐
tive, the usage is not much different from bpf_map_lookup_elem(map, &inode) except this helper enforces the
key must be an inode and the map must also be a BPF_MAP_TYPE_INODE_STORAGE.
Underneath, the value is stored locally at inode instead of the map. The map is used as the bpf-local-storage
"type". The bpf-local-storage "type" (i.e. the map) is searched against all bpf_local_storage residing at in‐
ode.
An optional flags (BPF_LOCAL_STORAGE_GET_F_CREATE) can be used such that a new bpf_local_storage will be cre‐
ated if one does not exist. value can be used together with BPF_LOCAL_STORAGE_GET_F_CREATE to specify the
initial value of a bpf_local_storage. If value is NULL, the new bpf_local_storage will be zero initialized.
Return A bpf_local_storage pointer is returned on success.
NULL if not found or there was an error in adding a new bpf_local_storage.
int bpf_inode_storage_delete(struct bpf_map *map, void *inode)
Description
Delete a bpf_local_storage from an inode.
Return 0 on success.
-ENOENT if the bpf_local_storage cannot be found.
long bpf_d_path(struct path *path, char *buf, u32 sz)
Description
Return full path for given struct path object, which needs to be the kernel BTF path object. The path is re‐
turned in the provided buffer buf of size sz and is zero terminated.
Return On success, the strictly positive length of the string, including the trailing NUL character. On error, a neg‐
ative value.
long bpf_copy_from_user(void *dst, u32 size, const void *user_ptr)
Description
Read size bytes from user space address user_ptr and store the data in dst. This is a wrapper of
copy_from_user().
Return 0 on success, or a negative error in case of failure.
long bpf_snprintf_btf(char *str, u32 str_size, struct btf_ptr *ptr, u32 btf_ptr_size, u64 flags)
Description
Use BTF to store a string representation of ptr->ptr in str, using ptr->type_id. This value should specify
the type that ptr->ptr points to. LLVM __builtin_btf_type_id(type, 1) can be used to look up vmlinux BTF type
ids. Traversing the data structure using BTF, the type information and values are stored in the first str_size
- 1 bytes of str. Safe copy of the pointer data is carried out to avoid kernel crashes during operation.
Smaller types can use string space on the stack; larger programs can use map data to store the string repre‐
sentation.
The string can be subsequently shared with userspace via bpf_perf_event_output() or ring buffer interfaces.
bpf_trace_printk() is to be avoided as it places too small a limit on string size to be useful.
flags is a combination of
BTF_F_COMPACT
no formatting around type information
BTF_F_NONAME
no struct/union member names/types
BTF_F_PTR_RAW
show raw (unobfuscated) pointer values; equivalent to printk specifier %px.
BTF_F_ZERO
show zero-valued struct/union members; they are not displayed by default
Return The number of bytes that were written (or would have been written if output had to be truncated due to string
size), or a negative error in cases of failure.
long bpf_seq_printf_btf(struct seq_file *m, struct btf_ptr *ptr, u32 ptr_size, u64 flags)
Description
Use BTF to write to seq_write a string representation of ptr->ptr, using ptr->type_id as per
bpf_snprintf_btf(). flags are identical to those used for bpf_snprintf_btf.
Return 0 on success or a negative error in case of failure.
u64 bpf_skb_cgroup_classid(struct sk_buff *skb)
Description
See bpf_get_cgroup_classid() for the main description. This helper differs from bpf_get_cgroup_classid() in
that the cgroup v1 net_cls class is retrieved only from the skb's associated socket instead of the current
process.
Return The id is returned or 0 in case the id could not be retrieved.
long bpf_redirect_neigh(u32 ifindex, struct bpf_redir_neigh *params, int plen, u64 flags)
Description
Redirect the packet to another net device of index ifindex and fill in L2 addresses from neighboring subsys‐
tem. This helper is somewhat similar to bpf_redirect(), except that it populates L2 addresses as well, mean‐
ing, internally, the helper relies on the neighbor lookup for the L2 address of the nexthop.
The helper will perform a FIB lookup based on the skb's networking header to get the address of the next hop,
unless this is supplied by the caller in the params argument. The plen argument indicates the len of params
and should be set to 0 if params is NULL.
The flags argument is reserved and must be 0. The helper is currently only supported for tc BPF program types,
and enabled for IPv4 and IPv6 protocols.
Return The helper returns TC_ACT_REDIRECT on success or TC_ACT_SHOT on error.
void *bpf_per_cpu_ptr(const void *percpu_ptr, u32 cpu)
Description
Take a pointer to a percpu ksym, percpu_ptr, and return a pointer to the percpu kernel variable on cpu. A ksym
is an extern variable decorated with '__ksym'. For ksym, there is a global var (either static or global) de‐
fined of the same name in the kernel. The ksym is percpu if the global var is percpu. The returned pointer
points to the global percpu var on cpu.
bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel, except that bpf_per_cpu_ptr() may re‐
turn NULL. This happens if cpu is larger than nr_cpu_ids. The caller of bpf_per_cpu_ptr() must check the re‐
turned value.
Return A pointer pointing to the kernel percpu variable on cpu, or NULL, if cpu is invalid.
void *bpf_this_cpu_ptr(const void *percpu_ptr)
Description
Take a pointer to a percpu ksym, percpu_ptr, and return a pointer to the percpu kernel variable on this cpu.
See the description of 'ksym' in bpf_per_cpu_ptr().
bpf_this_cpu_ptr() has the same semantic as this_cpu_ptr() in the kernel. Different from bpf_per_cpu_ptr(), it
would never return NULL.
Return A pointer pointing to the kernel percpu variable on this cpu.
long bpf_redirect_peer(u32 ifindex, u64 flags)
Description
Redirect the packet to another net device of index ifindex. This helper is somewhat similar to bpf_redi‐
rect(), except that the redirection happens to the ifindex' peer device and the netns switch takes place from
ingress to ingress without going through the CPU's backlog queue.
The flags argument is reserved and must be 0. The helper is currently only supported for tc BPF program types
at the ingress hook and for veth device types. The peer device must reside in a different network namespace.
Return The helper returns TC_ACT_REDIRECT on success or TC_ACT_SHOT on error.
void *bpf_task_storage_get(struct bpf_map *map, struct task_struct *task, void *value, u64 flags)
Description
Get a bpf_local_storage from the task.
Logically, it could be thought of as getting the value from a map with task as the key. From this perspec‐
tive, the usage is not much different from bpf_map_lookup_elem(map, &task) except this helper enforces the
key must be a task_struct and the map must also be a BPF_MAP_TYPE_TASK_STORAGE.
Underneath, the value is stored locally at task instead of the map. The map is used as the bpf-local-storage
"type". The bpf-local-storage "type" (i.e. the map) is searched against all bpf_local_storage residing at
task.
An optional flags (BPF_LOCAL_STORAGE_GET_F_CREATE) can be used such that a new bpf_local_storage will be cre‐
ated if one does not exist. value can be used together with BPF_LOCAL_STORAGE_GET_F_CREATE to specify the
initial value of a bpf_local_storage. If value is NULL, the new bpf_local_storage will be zero initialized.
Return A bpf_local_storage pointer is returned on success.
NULL if not found or there was an error in adding a new bpf_local_storage.
long bpf_task_storage_delete(struct bpf_map *map, struct task_struct *task)
Description
Delete a bpf_local_storage from a task.
Return 0 on success.
-ENOENT if the bpf_local_storage cannot be found.
struct task_struct *bpf_get_current_task_btf(void)
Description
Return a BTF pointer to the "current" task. This pointer can also be used in helpers that accept an
ARG_PTR_TO_BTF_ID of type task_struct.
Return Pointer to the current task.
long bpf_bprm_opts_set(struct linux_binprm *bprm, u64 flags)
Description
Set or clear certain options on bprm:
BPF_F_BPRM_SECUREEXEC Set the secureexec bit which sets the AT_SECURE auxv for glibc. The bit is cleared if
the flag is not specified.
Return -EINVAL if invalid flags are passed, zero otherwise.
u64 bpf_ktime_get_coarse_ns(void)
Description
Return a coarse-grained version of the time elapsed since system boot, in nanoseconds. Does not include time
the system was suspended.
See: clock_gettime(CLOCK_MONOTONIC_COARSE)
Return Current ktime.
long bpf_ima_inode_hash(struct inode *inode, void *dst, u32 size)
Description
Returns the stored IMA hash of the inode (if it's available). If the hash is larger than size, then only size
bytes will be copied to dst
Return The hash_algo is returned on success, -EOPNOTSUP if IMA is disabled or -EINVAL if invalid arguments are
passed.
struct socket *bpf_sock_from_file(struct file *file)
Description
If the given file represents a socket, returns the associated socket.
Return A pointer to a struct socket on success or NULL if the file is not a socket.
long bpf_check_mtu(void *ctx, u32 ifindex, u32 *mtu_len, s32 len_diff, u64 flags)
Description
Check packet size against exceeding MTU of net device (based on ifindex). This helper will likely be used in
combination with helpers that adjust/change the packet size.
The argument len_diff can be used for querying with a planned size change. This allows to check MTU prior to
changing packet ctx. Providing a len_diff adjustment that is larger than the actual packet size (resulting in
negative packet size) will in principle not exceed the MTU, which is why it is not considered a failure.
Other BPF helpers are needed for performing the planned size change; therefore the responsibility for catching
a negative packet size belongs in those helpers.
Specifying ifindex zero means the MTU check is performed against the current net device. This is practical if
this isn't used prior to redirect.
On input mtu_len must be a valid pointer, else verifier will reject BPF program. If the value mtu_len is ini‐
tialized to zero then the ctx packet size is use. When value mtu_len is provided as input this specify the L3
length that the MTU check is done against. Remember XDP and TC length operate at L2, but this value is L3 as
this correlate to MTU and IP-header tot_len values which are L3 (similar behavior as bpf_fib_lookup).
The Linux kernel route table can configure MTUs on a more specific per route level, which is not provided by
this helper. For route level MTU checks use the bpf_fib_lookup() helper.
ctx is either struct xdp_md for XDP programs or struct sk_buff for tc cls_act programs.
The flags argument can be a combination of one or more of the following values:
BPF_MTU_CHK_SEGS
This flag will only works for ctx struct sk_buff. If packet context contains extra packet segment buf‐
fers (often knows as GSO skb), then MTU check is harder to check at this point, because in transmit
path it is possible for the skb packet to get re-segmented (depending on net device features). This
could still be a MTU violation, so this flag enables performing MTU check against segments, with a dif‐
ferent violation return code to tell it apart. Check cannot use len_diff.
On return mtu_len pointer contains the MTU value of the net device. Remember the net device configured MTU is
the L3 size, which is returned here and XDP and TC length operate at L2. Helper take this into account for
you, but remember when using MTU value in your BPF-code.
Return
• 0 on success, and populate MTU value in mtu_len pointer.
• < 0 if any input argument is invalid (mtu_len not updated)
MTU violations return positive values, but also populate MTU value in mtu_len pointer, as this can be needed
for implementing PMTU handing:
• BPF_MTU_CHK_RET_FRAG_NEEDED
• BPF_MTU_CHK_RET_SEGS_TOOBIG
long bpf_for_each_map_elem(struct bpf_map *map, void *callback_fn, void *callback_ctx, u64 flags)
Description
For each element in map, call callback_fn function with map, callback_ctx and other map-specific parameters.
The callback_fn should be a static function and the callback_ctx should be a pointer to the stack. The flags
is used to control certain aspects of the helper. Currently, the flags must be 0.
The following are a list of supported map types and their respective expected callback signatures:
BPF_MAP_TYPE_HASH, BPF_MAP_TYPE_PERCPU_HASH, BPF_MAP_TYPE_LRU_HASH, BPF_MAP_TYPE_LRU_PERCPU_HASH,
BPF_MAP_TYPE_ARRAY, BPF_MAP_TYPE_PERCPU_ARRAY
long (*callback_fn)(struct bpf_map *map, const void *key, void *value, void *ctx);
For per_cpu maps, the map_value is the value on the cpu where the bpf_prog is running.
If callback_fn return 0, the helper will continue to the next element. If return value is 1, the helper will
skip the rest of elements and return. Other return values are not used now.
Return The number of traversed map elements for success, -EINVAL for invalid flags.
long bpf_snprintf(char *str, u32 str_size, const char *fmt, u64 *data, u32 data_len)
Description
Outputs a string into the str buffer of size str_size based on a format string stored in a read-only map
pointed by fmt.
Each format specifier in fmt corresponds to one u64 element in the data array. For strings and pointers where
pointees are accessed, only the pointer values are stored in the data array. The data_len is the size of data
in bytes - must be a multiple of 8.
Formats %s and %p{i,I}{4,6} require to read kernel memory. Reading kernel memory may fail due to either in‐
valid address or valid address but requiring a major memory fault. If reading kernel memory fails, the string
for %s will be an empty string, and the ip address for %p{i,I}{4,6} will be 0. Not returning error to bpf
program is consistent with what bpf_trace_printk() does for now.
Return The strictly positive length of the formatted string, including the trailing zero character. If the return
value is greater than str_size, str contains a truncated string, guaranteed to be zero-terminated except when
str_size is 0.
Or -EBUSY if the per-CPU memory copy buffer is busy.
long bpf_sys_bpf(u32 cmd, void *attr, u32 attr_size)
Description
Execute bpf syscall with given arguments.
Return A syscall result.
long bpf_btf_find_by_name_kind(char *name, int name_sz, u32 kind, int flags)
Description
Find BTF type with given name and kind in vmlinux BTF or in module's BTFs.
Return Returns btf_id and btf_obj_fd in lower and upper 32 bits.
long bpf_sys_close(u32 fd)
Description
Execute close syscall for given FD.
Return A syscall result.
long bpf_timer_init(struct bpf_timer *timer, struct bpf_map *map, u64 flags)
Description
Initialize the timer. First 4 bits of flags specify clockid. Only CLOCK_MONOTONIC, CLOCK_REALTIME,
CLOCK_BOOTTIME are allowed. All other bits of flags are reserved. The verifier will reject the program if
timer is not from the same map.
Return 0 on success. -EBUSY if timer is already initialized. -EINVAL if invalid flags are passed. -EPERM if timer
is in a map that doesn't have any user references. The user space should either hold a file descriptor to a
map with timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the
map will be cancelled and freed.
long bpf_timer_set_callback(struct bpf_timer *timer, void *callback_fn)
Description
Configure the timer to call callback_fn static function.
Return 0 on success. -EINVAL if timer was not initialized with bpf_timer_init() earlier. -EPERM if timer is in a
map that doesn't have any user references. The user space should either hold a file descriptor to a map with
timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the map will
be cancelled and freed.
long bpf_timer_start(struct bpf_timer *timer, u64 nsecs, u64 flags)
Description
Set timer expiration N nanoseconds from the current time. The configured callback will be invoked in soft irq
context on some cpu and will not repeat unless another bpf_timer_start() is made. In such case the next invo‐
cation can migrate to a different cpu. Since struct bpf_timer is a field inside map element the map owns the
timer. The bpf_timer_set_callback() will increment refcnt of BPF program to make sure that callback_fn code
stays valid. When user space reference to a map reaches zero all timers in a map are cancelled and corre‐
sponding program's refcnts are decremented. This is done to make sure that Ctrl-C of a user process doesn't
leave any timers running. If map is pinned in bpffs the callback_fn can re-arm itself indefinitely.
bpf_map_update/delete_elem() helpers and user space sys_bpf commands cancel and free the timer in the given
map element. The map can contain timers that invoke callback_fn-s from different programs. The same call‐
back_fn can serve different timers from different maps if key/value layout matches across maps. Every
bpf_timer_set_callback() can have different callback_fn.
Return 0 on success. -EINVAL if timer was not initialized with bpf_timer_init() earlier or invalid flags are passed.
long bpf_timer_cancel(struct bpf_timer *timer)
Description
Cancel the timer and wait for callback_fn to finish if it was running.
Return 0 if the timer was not active. 1 if the timer was active. -EINVAL if timer was not initialized with
bpf_timer_init() earlier. -EDEADLK if callback_fn tried to call bpf_timer_cancel() on its own timer which
would have led to a deadlock otherwise.
u64 bpf_get_func_ip(void *ctx)
Description
Get address of the traced function (for tracing and kprobe programs).
Return Address of the traced function. 0 for kprobes placed within the function (not at the entry).
u64 bpf_get_attach_cookie(void *ctx)
Description
Get bpf_cookie value provided (optionally) during the program attachment. It might be different for each indi‐
vidual attachment, even if BPF program itself is the same. Expects BPF program context ctx as a first argu‐
ment.
Supported for the following program types:
• kprobe/uprobe;
• tracepoint;
• perf_event.
Return Value specified by user at BPF link creation/attachment time or 0, if it was not specified.
long bpf_task_pt_regs(struct task_struct *task)
Description
Get the struct pt_regs associated with task.
Return A pointer to struct pt_regs.
long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
Description
Get branch trace from hardware engines like Intel LBR. The hardware engine is stopped shortly after the helper
is called. Therefore, the user need to filter branch entries based on the actual use case. To capture branch
trace before the trigger point of the BPF program, the helper should be called at the beginning of the BPF
program.
The data is stored as struct perf_branch_entry into output buffer entries. size is the size of entries in
bytes. flags is reserved for now and must be zero.
Return On success, number of bytes written to buf. On error, a negative value.
-EINVAL if flags is not zero.
-ENOENT if architecture does not support branch records.
long bpf_trace_vprintk(const char *fmt, u32 fmt_size, const void *data, u32 data_len)
Description
Behaves like bpf_trace_printk() helper, but takes an array of u64 to format and can handle more format args as
a result.
Arguments are to be used as in bpf_seq_printf() helper.
Return The number of bytes written to the buffer, or a negative error in case of failure.
struct unix_sock *bpf_skc_to_unix_sock(void *sk)
Description
Dynamically cast a sk pointer to a unix_sock pointer.
Return sk if casting is valid, or NULL otherwise.
long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags, u64 *res)
Description
Get the address of a kernel symbol, returned in res. res is set to 0 if the symbol is not found.
Return On success, zero. On error, a negative value.
-EINVAL if flags is not zero.
-EINVAL if string name is not the same size as name_sz.
-ENOENT if symbol is not found.
-EPERM if caller does not have permission to obtain kernel address.
long bpf_find_vma(struct task_struct *task, u64 addr, void *callback_fn, void *callback_ctx, u64 flags)
Description
Find vma of task that contains addr, call callback_fn function with task, vma, and callback_ctx. The call‐
back_fn should be a static function and the callback_ctx should be a pointer to the stack. The flags is used
to control certain aspects of the helper. Currently, the flags must be 0.
The expected callback signature is
long (*callback_fn)(struct task_struct *task, struct vm_area_struct *vma, void *callback_ctx);
Return 0 on success. -ENOENT if task->mm is NULL, or no vma contains addr. -EBUSY if failed to try lock mmap_lock.
-EINVAL for invalid flags.
long bpf_loop(u32 nr_loops, void *callback_fn, void *callback_ctx, u64 flags)
Description
For nr_loops, call callback_fn function with callback_ctx as the context parameter. The callback_fn should be
a static function and the callback_ctx should be a pointer to the stack. The flags is used to control certain
aspects of the helper. Currently, the flags must be 0. Currently, nr_loops is limited to 1 << 23 (~8 million)
loops.
long (*callback_fn)(u32 index, void *ctx);
where index is the current index in the loop. The index is zero-indexed.
If callback_fn returns 0, the helper will continue to the next loop. If return value is 1, the helper will
skip the rest of the loops and return. Other return values are not used now, and will be rejected by the veri‐
fier.
Return The number of loops performed, -EINVAL for invalid flags, -E2BIG if nr_loops exceeds the maximum number of
loops.
long bpf_strncmp(const char *s1, u32 s1_sz, const char *s2)
Description
Do strncmp() between s1 and s2. s1 doesn't need to be null-terminated and s1_sz is the maximum storage size of
s1. s2 must be a read-only string.
Return An integer less than, equal to, or greater than zero if the first s1_sz bytes of s1 is found to be less than,
to match, or be greater than s2.
long bpf_get_func_arg(void *ctx, u32 n, u64 *value)
Description
Get n-th argument register (zero based) of the traced function (for tracing programs) returned in value.
Return 0 on success. -EINVAL if n >= argument register count of traced function.
long bpf_get_func_ret(void *ctx, u64 *value)
Description
Get return value of the traced function (for tracing programs) in value.
Return 0 on success. -EOPNOTSUPP for tracing programs other than BPF_TRACE_FEXIT or BPF_MODIFY_RETURN.
long bpf_get_func_arg_cnt(void *ctx)
Description
Get number of registers of the traced function (for tracing programs) where function arguments are stored in
these registers.
Return The number of argument registers of the traced function.
int bpf_get_retval(void)
Description
Get the BPF program's return value that will be returned to the upper layers.
This helper is currently supported by cgroup programs and only by the hooks where BPF program's return value
is returned to the userspace via errno.
Return The BPF program's return value.
int bpf_set_retval(int retval)
Description
Set the BPF program's return value that will be returned to the upper layers.
This helper is currently supported by cgroup programs and only by the hooks where BPF program's return value
is returned to the userspace via errno.
Note that there is the following corner case where the program exports an error via bpf_set_retval but signals
success via 'return 1':
bpf_set_retval(-EPERM); return 1;
In this case, the BPF program's return value will use helper's -EPERM. This still holds true for
cgroup/bind{4,6} which supports extra 'return 3' success case.
Return 0 on success, or a negative error in case of failure.
u64 bpf_xdp_get_buff_len(struct xdp_buff *xdp_md)
Description
Get the total size of a given xdp buff (linear and paged area)
Return The total size of a given xdp buffer.
long bpf_xdp_load_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
Description
This helper is provided as an easy way to load data from a xdp buffer. It can be used to load len bytes from
offset from the frame associated to xdp_md, into the buffer pointed by buf.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_store_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
Description
Store len bytes from buffer buf into the frame associated to xdp_md, at offset.
Return 0 on success, or a negative error in case of failure.
long bpf_copy_from_user_task(void *dst, u32 size, const void *user_ptr, struct task_struct *tsk, u64 flags)
Description
Read size bytes from user space address user_ptr in tsk's address space, and stores the data in dst. flags is
not used yet and is provided for future extensibility. This helper can only be used by sleepable programs.
Return 0 on success, or a negative error in case of failure. On error dst buffer is zeroed out.
long bpf_skb_set_tstamp(struct sk_buff *skb, u64 tstamp, u32 tstamp_type)
Description
Change the __sk_buff->tstamp_type to tstamp_type and set tstamp to the __sk_buff->tstamp together.
If there is no need to change the __sk_buff->tstamp_type, the tstamp value can be directly written to
__sk_buff->tstamp instead.
BPF_SKB_TSTAMP_DELIVERY_MONO is the only tstamp that will be kept during bpf_redirect_*(). A non zero tstamp
must be used with the BPF_SKB_TSTAMP_DELIVERY_MONO tstamp_type.
A BPF_SKB_TSTAMP_UNSPEC tstamp_type can only be used with a zero tstamp.
Only IPv4 and IPv6 skb->protocol are supported.
This function is most useful when it needs to set a mono delivery time to __sk_buff->tstamp and then bpf_redi‐
rect_*() to the egress of an iface. For example, changing the (rcv) timestamp in __sk_buff->tstamp at ingress
to a mono delivery time and then bpf_redirect_*() to sch_fq@phy-dev.
Return 0 on success. -EINVAL for invalid input -EOPNOTSUPP for unsupported protocol
long bpf_ima_file_hash(struct file *file, void *dst, u32 size)
Description
Returns a calculated IMA hash of the file. If the hash is larger than size, then only size bytes will be
copied to dst
Return The hash_algo is returned on success, -EOPNOTSUP if the hash calculation failed or -EINVAL if invalid argu‐
ments are passed.
void *bpf_kptr_xchg(void *map_value, void *ptr)
Description
Exchange kptr at pointer map_value with ptr, and return the old value. ptr can be NULL, otherwise it must be a
referenced pointer which will be released when this helper is called.
Return The old value of kptr (which can be NULL). The returned pointer if not NULL, is a reference which must be re‐
leased using its corresponding release function, or moved into a BPF map before program exit.
void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void *key, u32 cpu)
Description
Perform a lookup in percpu map for an entry associated to key on cpu.
Return Map value associated to key on cpu, or NULL if no entry was found or cpu is invalid.
struct mptcp_sock *bpf_skc_to_mptcp_sock(void *sk)
Description
Dynamically cast a sk pointer to a mptcp_sock pointer.
Return sk if casting is valid, or NULL otherwise.
long bpf_dynptr_from_mem(void *data, u32 size, u64 flags, struct bpf_dynptr *ptr)
Description
Get a dynptr to local memory data.
data must be a ptr to a map value. The maximum size supported is DYNPTR_MAX_SIZE. flags is currently unused.
Return 0 on success, -E2BIG if the size exceeds DYNPTR_MAX_SIZE, -EINVAL if flags is not 0.
long bpf_ringbuf_reserve_dynptr(void *ringbuf, u32 size, u64 flags, struct bpf_dynptr *ptr)
Description
Reserve size bytes of payload in a ring buffer ringbuf through the dynptr interface. flags must be 0.
Please note that a corresponding bpf_ringbuf_submit_dynptr or bpf_ringbuf_discard_dynptr must be called on
ptr, even if the reservation fails. This is enforced by the verifier.
Return 0 on success, or a negative error in case of failure.
void bpf_ringbuf_submit_dynptr(struct bpf_dynptr *ptr, u64 flags)
Description
Submit reserved ring buffer sample, pointed to by data, through the dynptr interface. This is a no-op if the
dynptr is invalid/null.
For more information on flags, please see 'bpf_ringbuf_submit'.
Return Nothing. Always succeeds.
void bpf_ringbuf_discard_dynptr(struct bpf_dynptr *ptr, u64 flags)
Description
Discard reserved ring buffer sample through the dynptr interface. This is a no-op if the dynptr is in‐
valid/null.
For more information on flags, please see 'bpf_ringbuf_discard'.
Return Nothing. Always succeeds.
long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset, u64 flags)
Description
Read len bytes from src into dst, starting from offset into src. flags is currently unused.
Return 0 on success, -E2BIG if offset + len exceeds the length of src's data, -EINVAL if src is an invalid dynptr or
if flags is not 0.
long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len, u64 flags)
Description
Write len bytes from src into dst, starting from offset into dst. flags is currently unused.
Return 0 on success, -E2BIG if offset + len exceeds the length of dst's data, -EINVAL if dst is an invalid dynptr or
if dst is a read-only dynptr or if flags is not 0.
void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
Description
Get a pointer to the underlying dynptr data.
len must be a statically known value. The returned data slice is invalidated whenever the dynptr is invali‐
dated.
Return Pointer to the underlying dynptr data, NULL if the dynptr is read-only, if the dynptr is invalid, or if the
offset and length is out of bounds.
s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th, u32 th_len)
Description
Try to issue a SYN cookie for the packet with corresponding IPv4/TCP headers, iph and th, without depending on
a listening socket.
iph points to the IPv4 header.
th points to the start of the TCP header, while th_len contains the length of the TCP header (at least
sizeof(struct tcphdr)).
Return On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for
that cookie, and the top 16 bits are unused.
On failure, the returned value is one of the following:
-EINVAL if th_len is invalid.
s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th, u32 th_len)
Description
Try to issue a SYN cookie for the packet with corresponding IPv6/TCP headers, iph and th, without depending on
a listening socket.
iph points to the IPv6 header.
th points to the start of the TCP header, while th_len contains the length of the TCP header (at least
sizeof(struct tcphdr)).
Return On success, lower 32 bits hold the generated SYN cookie in followed by 16 bits which hold the MSS value for
that cookie, and the top 16 bits are unused.
On failure, the returned value is one of the following:
-EINVAL if th_len is invalid.
-EPROTONOSUPPORT if CONFIG_IPV6 is not builtin.
long bpf_tcp_raw_check_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th)
Description
Check whether iph and th contain a valid SYN cookie ACK without depending on a listening socket.
iph points to the IPv4 header.
th points to the TCP header.
Return 0 if iph and th are a valid SYN cookie ACK.
On failure, the returned value is one of the following:
-EACCES if the SYN cookie is not valid.
long bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th)
Description
Check whether iph and th contain a valid SYN cookie ACK without depending on a listening socket.
iph points to the IPv6 header.
th points to the TCP header.
Return 0 if iph and th are a valid SYN cookie ACK.
On failure, the returned value is one of the following:
-EACCES if the SYN cookie is not valid.
-EPROTONOSUPPORT if CONFIG_IPV6 is not builtin.
u64 bpf_ktime_get_tai_ns(void)
Description
A nonsettable system-wide clock derived from wall-clock time but ignoring leap seconds. This clock does not
experience discontinuities and backwards jumps caused by NTP inserting leap seconds as CLOCK_REALTIME does.
See: clock_gettime(CLOCK_TAI)
Return Current ktime.
long bpf_user_ringbuf_drain(struct bpf_map *map, void *callback_fn, void *ctx, u64 flags)
Description
Drain samples from the specified user ring buffer, and invoke the provided callback for each such sample:
long (*callback_fn)(struct bpf_dynptr *dynptr, void *ctx);
If callback_fn returns 0, the helper will continue to try and drain the next sample, up to a maximum of
BPF_MAX_USER_RINGBUF_SAMPLES samples. If the return value is 1, the helper will skip the rest of the samples
and return. Other return values are not used now, and will be rejected by the verifier.
Return The number of drained samples if no error was encountered while draining samples, or 0 if no samples were
present in the ring buffer. If a user-space producer was epoll-waiting on this map, and at least one sample
was drained, they will receive an event notification notifying them of available space in the ring buffer. If
the BPF_RB_NO_WAKEUP flag is passed to this function, no wakeup notification will be sent. If the
BPF_RB_FORCE_WAKEUP flag is passed, a wakeup notification will be sent even if no sample was drained.
On failure, the returned value is one of the following:
-EBUSY if the ring buffer is contended, and another calling context was concurrently draining the ring buffer.
-EINVAL if user-space is not properly tracking the ring buffer due to the producer position not being aligned
to 8 bytes, a sample not being aligned to 8 bytes, or the producer position not matching the advertised length
of a sample.
-E2BIG if user-space has tried to publish a sample which is larger than the size of the ring buffer, or which
cannot fit within a struct bpf_dynptr.
EXAMPLES
Example usage for most of the eBPF helpers listed in this manual page are available within the Linux kernel sources, at the
following locations:
• samples/bpf/
• tools/testing/selftests/bpf/
LICENSE
eBPF programs can have an associated license, passed along with the bytecode instructions to the kernel when the programs
are loaded. The format for that string is identical to the one in use for kernel modules (Dual licenses, such as "Dual
BSD/GPL", may be used). Some helper functions are only accessible to programs that are compatible with the GNU Privacy Li‐
cense (GPL).
In order to use such helpers, the eBPF program must be loaded with the correct license string passed (via attr) to the bpf()
system call, and this generally translates into the C source code of the program containing a line similar to the following:
char ____license[] __attribute__((section("license"), used)) = "GPL";
IMPLEMENTATION
This manual page is an effort to document the existing eBPF helper functions. But as of this writing, the BPF sub-system is
under heavy development. New eBPF program or map types are added, along with new helper functions. Some helpers are occa‐
sionally made available for additional program types. So in spite of the efforts of the community, this page might not be
up-to-date. If you want to check by yourself what helper functions exist in your kernel, or what types of programs they can
support, here are some files among the kernel tree that you may be interested in:
• include/uapi/linux/bpf.h is the main BPF header. It contains the full list of all helper functions, as well as many other
BPF definitions including most of the flags, structs or constants used by the helpers.
• net/core/filter.c contains the definition of most network-related helper functions, and the list of program types from
which they can be used.
• kernel/trace/bpf_trace.c is the equivalent for most tracing program-related helpers.
• kernel/bpf/verifier.c contains the functions used to check that valid types of eBPF maps are used with a given helper
function.
• kernel/bpf/ directory contains other files in which additional helpers are defined (for cgroups, sockmaps, etc.).
• The bpftool utility can be used to probe the availability of helper functions on the system (as well as supported program
and map types, and a number of other parameters). To do so, run bpftool feature probe (see bpftool-feature(8) for de‐
tails). Add the unprivileged keyword to list features available to unprivileged users.
Compatibility between helper functions and program types can generally be found in the files where helper functions are de‐
fined. Look for the struct bpf_func_proto objects and for functions returning them: these functions contain a list of
helpers that a given program type can call. Note that the default: label of the switch ... case used to filter helpers can
call other functions, themselves allowing access to additional helpers. The requirement for GPL license is also in those
struct bpf_func_proto.
Compatibility between helper functions and map types can be found in the check_map_func_compatibility() function in file
kernel/bpf/verifier.c.
Helper functions that invalidate the checks on data and data_end pointers for network processing are listed in function
bpf_helper_changes_pkt_data() in file net/core/filter.c.
SEE ALSO
bpf(2), bpftool(8), cgroups(7), ip(8), perf_event_open(2), sendmsg(2), socket(7), tc-bpf(8)
Linux v6.1 2022-09-26 BPF-HELPERS(7)