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NAME
bpf - perform a command on an extended BPF map or program
SYNOPSIS
#include <linux/bpf.h>
int bpf(int cmd, union bpf_attr *attr, unsigned int size);
DESCRIPTION
The bpf() system call performs a range of operations related to extended Berkeley Packet Filters.
Extended BPF (or eBPF) is similar to the original ("classic") BPF (cBPF) used to filter network packets.
For both cBPF and eBPF programs, the kernel statically analyzes the programs before loading them, in
order to ensure that they cannot harm the running system.
eBPF extends cBPF in multiple ways, including the ability to call a fixed set of in-kernel helper
functions (via the BPF_CALL opcode extension provided by eBPF) and access shared data structures such as
eBPF maps.
Extended BPF Design/Architecture
eBPF maps are a generic data structure for storage of different data types. Data types are generally
treated as binary blobs, so a user just specifies the size of the key and the size of the value at map-
creation time. In other words, a key/value for a given map can have an arbitrary structure.
A user process can create multiple maps (with key/value-pairs being opaque bytes of data) and access them
via file descriptors. Different eBPF programs can access the same maps in parallel. It's up to the user
process and eBPF program to decide what they store inside maps.
There's one special map type, called a program array. This type of map stores file descriptors referring
to other eBPF programs. When a lookup in the map is performed, the program flow is redirected in-place
to the beginning of another eBPF program and does not return back to the calling program. The level of
nesting has a fixed limit of 32, so that infinite loops cannot be crafted. At run time, the program file
descriptors stored in the map can be modified, so program functionality can be altered based on specific
requirements. All programs referred to in a program-array map must have been previously loaded into the
kernel via bpf(). If a map lookup fails, the current program continues its execution. See
BPF_MAP_TYPE_PROG_ARRAY below for further details.
Generally, eBPF programs are loaded by the user process and automatically unloaded when the process
exits. In some cases, for example, tc-bpf(8), the program will continue to stay alive inside the kernel
even after the process that loaded the program exits. In that case, the tc subsystem holds a reference
to the eBPF program after the file descriptor has been closed by the user-space program. Thus, whether a
specific program continues to live inside the kernel depends on how it is further attached to a given
kernel subsystem after it was loaded via bpf().
Each eBPF program is a set of instructions that is safe to run until its completion. An in-kernel
verifier statically determines that the eBPF program terminates and is safe to execute. During
verification, the kernel increments reference counts for each of the maps that the eBPF program uses, so
that the attached maps can't be removed until the program is unloaded.
eBPF programs can be attached to different events. These events can be the arrival of network packets,
tracing events, classification events by network queueing disciplines (for eBPF programs attached to a
tc(8) classifier), and other types that may be added in the future. A new event triggers execution of
the eBPF program, which may store information about the event in eBPF maps. Beyond storing data, eBPF
programs may call a fixed set of in-kernel helper functions.
The same eBPF program can be attached to multiple events and different eBPF programs can access the same
map:
tracing tracing tracing packet packet packet
event A event B event C on eth0 on eth1 on eth2
| | | | | ^
| | | | v |
--> tracing <-- tracing socket tc ingress tc egress
prog_1 prog_2 prog_3 classifier action
| | | | prog_4 prog_5
|--- -----| |------| map_3 | |
map_1 map_2 --| map_4 |--
Arguments
The operation to be performed by the bpf() system call is determined by the cmd argument. Each operation
takes an accompanying argument, provided via attr, which is a pointer to a union of type bpf_attr (see
below). The unused fields and padding must be zeroed out before the call. The size argument is the size
of the union pointed to by attr.
The value provided in cmd is one of the following:
BPF_MAP_CREATE
Create a map and return a file descriptor that refers to the map. The close-on-exec file
descriptor flag (see fcntl(2)) is automatically enabled for the new file descriptor.
BPF_MAP_LOOKUP_ELEM
Look up an element by key in a specified map and return its value.
BPF_MAP_UPDATE_ELEM
Create or update an element (key/value pair) in a specified map.
BPF_MAP_DELETE_ELEM
Look up and delete an element by key in a specified map.
BPF_MAP_GET_NEXT_KEY
Look up an element by key in a specified map and return the key of the next element.
BPF_PROG_LOAD
Verify and load an eBPF program, returning a new file descriptor associated with the program. The
close-on-exec file descriptor flag (see fcntl(2)) is automatically enabled for the new file
descriptor.
The bpf_attr union consists of various anonymous structures that are used by different bpf()
commands:
union bpf_attr {
struct { /* Used by BPF_MAP_CREATE */
__u32 map_type;
__u32 key_size; /* size of key in bytes */
__u32 value_size; /* size of value in bytes */
__u32 max_entries; /* maximum number of entries
in a map */
};
struct { /* Used by BPF_MAP_*_ELEM and BPF_MAP_GET_NEXT_KEY
commands */
__u32 map_fd;
__aligned_u64 key;
union {
__aligned_u64 value;
__aligned_u64 next_key;
};
__u64 flags;
};
struct { /* Used by BPF_PROG_LOAD */
__u32 prog_type;
__u32 insn_cnt;
__aligned_u64 insns; /* 'const struct bpf_insn *' */
__aligned_u64 license; /* 'const char *' */
__u32 log_level; /* verbosity level of verifier */
__u32 log_size; /* size of user buffer */
__aligned_u64 log_buf; /* user supplied 'char *'
buffer */
__u32 kern_version;
/* checked when prog_type=kprobe
(since Linux 4.1) */
};
} __attribute__((aligned(8)));
eBPF maps
Maps are a generic data structure for storage of different types of data. They allow sharing of data
between eBPF kernel programs, and also between kernel and user-space applications.
Each map type has the following attributes:
• type
• maximum number of elements
• key size in bytes
• value size in bytes
The following wrapper functions demonstrate how various bpf() commands can be used to access the maps.
The functions use the cmd argument to invoke different operations.
BPF_MAP_CREATE
The BPF_MAP_CREATE command creates a new map, returning a new file descriptor that refers to the
map.
int
bpf_create_map(enum bpf_map_type map_type,
unsigned int key_size,
unsigned int value_size,
unsigned int max_entries)
{
union bpf_attr attr = {
.map_type = map_type,
.key_size = key_size,
.value_size = value_size,
.max_entries = max_entries
};
return bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
}
The new map has the type specified by map_type, and attributes as specified in key_size,
value_size, and max_entries. On success, this operation returns a file descriptor. On error, -1
is returned and errno is set to EINVAL, EPERM, or ENOMEM.
The key_size and value_size attributes will be used by the verifier during program loading to
check that the program is calling bpf_map_*_elem() helper functions with a correctly initialized
key and to check that the program doesn't access the map element value beyond the specified
value_size. For example, when a map is created with a key_size of 8 and the eBPF program calls
bpf_map_lookup_elem(map_fd, fp - 4)
the program will be rejected, since the in-kernel helper function
bpf_map_lookup_elem(map_fd, void *key)
expects to read 8 bytes from the location pointed to by key, but the fp - 4 (where fp is the top
of the stack) starting address will cause out-of-bounds stack access.
Similarly, when a map is created with a value_size of 1 and the eBPF program contains
value = bpf_map_lookup_elem(...);
*(u32 *) value = 1;
the program will be rejected, since it accesses the value pointer beyond the specified 1 byte
value_size limit.
Currently, the following values are supported for map_type:
enum bpf_map_type {
BPF_MAP_TYPE_UNSPEC, /* Reserve 0 as invalid map type */
BPF_MAP_TYPE_HASH,
BPF_MAP_TYPE_ARRAY,
BPF_MAP_TYPE_PROG_ARRAY,
BPF_MAP_TYPE_PERF_EVENT_ARRAY,
BPF_MAP_TYPE_PERCPU_HASH,
BPF_MAP_TYPE_PERCPU_ARRAY,
BPF_MAP_TYPE_STACK_TRACE,
BPF_MAP_TYPE_CGROUP_ARRAY,
BPF_MAP_TYPE_LRU_HASH,
BPF_MAP_TYPE_LRU_PERCPU_HASH,
BPF_MAP_TYPE_LPM_TRIE,
BPF_MAP_TYPE_ARRAY_OF_MAPS,
BPF_MAP_TYPE_HASH_OF_MAPS,
BPF_MAP_TYPE_DEVMAP,
BPF_MAP_TYPE_SOCKMAP,
BPF_MAP_TYPE_CPUMAP,
BPF_MAP_TYPE_XSKMAP,
BPF_MAP_TYPE_SOCKHASH,
BPF_MAP_TYPE_CGROUP_STORAGE,
BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
BPF_MAP_TYPE_QUEUE,
BPF_MAP_TYPE_STACK,
/* See /usr/include/linux/bpf.h for the full list. */
};
map_type selects one of the available map implementations in the kernel. For all map types, eBPF
programs access maps with the same bpf_map_lookup_elem() and bpf_map_update_elem() helper
functions. Further details of the various map types are given below.
BPF_MAP_LOOKUP_ELEM
The BPF_MAP_LOOKUP_ELEM command looks up an element with a given key in the map referred to by the
file descriptor fd.
int
bpf_lookup_elem(int fd, const void *key, void *value)
{
union bpf_attr attr = {
.map_fd = fd,
.key = ptr_to_u64(key),
.value = ptr_to_u64(value),
};
return bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
}
If an element is found, the operation returns zero and stores the element's value into value,
which must point to a buffer of value_size bytes.
If no element is found, the operation returns -1 and sets errno to ENOENT.
BPF_MAP_UPDATE_ELEM
The BPF_MAP_UPDATE_ELEM command creates or updates an element with a given key/value in the map
referred to by the file descriptor fd.
int
bpf_update_elem(int fd, const void *key, const void *value,
uint64_t flags)
{
union bpf_attr attr = {
.map_fd = fd,
.key = ptr_to_u64(key),
.value = ptr_to_u64(value),
.flags = flags,
};
return bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
}
The flags argument should be specified as one of the following:
BPF_ANY
Create a new element or update an existing element.
BPF_NOEXIST
Create a new element only if it did not exist.
BPF_EXIST
Update an existing element.
On success, the operation returns zero. On error, -1 is returned and errno is set to EINVAL,
EPERM, ENOMEM, or E2BIG. E2BIG indicates that the number of elements in the map reached the
max_entries limit specified at map creation time. EEXIST will be returned if flags specifies
BPF_NOEXIST and the element with key already exists in the map. ENOENT will be returned if flags
specifies BPF_EXIST and the element with key doesn't exist in the map.
BPF_MAP_DELETE_ELEM
The BPF_MAP_DELETE_ELEM command deletes the element whose key is key from the map referred to by
the file descriptor fd.
int
bpf_delete_elem(int fd, const void *key)
{
union bpf_attr attr = {
.map_fd = fd,
.key = ptr_to_u64(key),
};
return bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr));
}
On success, zero is returned. If the element is not found, -1 is returned and errno is set to
ENOENT.
BPF_MAP_GET_NEXT_KEY
The BPF_MAP_GET_NEXT_KEY command looks up an element by key in the map referred to by the file
descriptor fd and sets the next_key pointer to the key of the next element.
int
bpf_get_next_key(int fd, const void *key, void *next_key)
{
union bpf_attr attr = {
.map_fd = fd,
.key = ptr_to_u64(key),
.next_key = ptr_to_u64(next_key),
};
return bpf(BPF_MAP_GET_NEXT_KEY, &attr, sizeof(attr));
}
If key is found, the operation returns zero and sets the next_key pointer to the key of the next
element. If key is not found, the operation returns zero and sets the next_key pointer to the key
of the first element. If key is the last element, -1 is returned and errno is set to ENOENT.
Other possible errno values are ENOMEM, EFAULT, EPERM, and EINVAL. This method can be used to
iterate over all elements in the map.
close(map_fd)
Delete the map referred to by the file descriptor map_fd. When the user-space program that
created a map exits, all maps will be deleted automatically (but see NOTES).
eBPF map types
The following map types are supported:
BPF_MAP_TYPE_HASH
Hash-table maps have the following characteristics:
• Maps are created and destroyed by user-space programs. Both user-space and eBPF programs can
perform lookup, update, and delete operations.
• The kernel takes care of allocating and freeing key/value pairs.
• The map_update_elem() helper will fail to insert new element when the max_entries limit is
reached. (This ensures that eBPF programs cannot exhaust memory.)
• map_update_elem() replaces existing elements atomically.
Hash-table maps are optimized for speed of lookup.
BPF_MAP_TYPE_ARRAY
Array maps have the following characteristics:
• Optimized for fastest possible lookup. In the future the verifier/JIT compiler may recognize
lookup() operations that employ a constant key and optimize it into constant pointer. It is
possible to optimize a non-constant key into direct pointer arithmetic as well, since pointers
and value_size are constant for the life of the eBPF program. In other words,
array_map_lookup_elem() may be 'inlined' by the verifier/JIT compiler while preserving
concurrent access to this map from user space.
• All array elements pre-allocated and zero initialized at init time
• The key is an array index, and must be exactly four bytes.
• map_delete_elem() fails with the error EINVAL, since elements cannot be deleted.
• map_update_elem() replaces elements in a nonatomic fashion; for atomic updates, a hash-table
map should be used instead. There is however one special case that can also be used with
arrays: the atomic built-in __sync_fetch_and_add() can be used on 32 and 64 bit atomic
counters. For example, it can be applied on the whole value itself if it represents a single
counter, or in case of a structure containing multiple counters, it could be used on individual
counters. This is quite often useful for aggregation and accounting of events.
Among the uses for array maps are the following:
• As "global" eBPF variables: an array of 1 element whose key is (index) 0 and where the value is
a collection of 'global' variables which eBPF programs can use to keep state between events.
• Aggregation of tracing events into a fixed set of buckets.
• Accounting of networking events, for example, number of packets and packet sizes.
BPF_MAP_TYPE_PROG_ARRAY (since Linux 4.2)
A program array map is a special kind of array map whose map values contain only file descriptors
referring to other eBPF programs. Thus, both the key_size and value_size must be exactly four
bytes. This map is used in conjunction with the bpf_tail_call() helper.
This means that an eBPF program with a program array map attached to it can call from kernel side
into
void bpf_tail_call(void *context, void *prog_map,
unsigned int index);
and therefore replace its own program flow with the one from the program at the given program
array slot, if present. This can be regarded as kind of a jump table to a different eBPF program.
The invoked program will then reuse the same stack. When a jump into the new program has been
performed, it won't return to the old program anymore.
If no eBPF program is found at the given index of the program array (because the map slot doesn't
contain a valid program file descriptor, the specified lookup index/key is out of bounds, or the
limit of 32 nested calls has been exceed), execution continues with the current eBPF program.
This can be used as a fall-through for default cases.
A program array map is useful, for example, in tracing or networking, to handle individual system
calls or protocols in their own subprograms and use their identifiers as an individual map index.
This approach may result in performance benefits, and also makes it possible to overcome the
maximum instruction limit of a single eBPF program. In dynamic environments, a user-space daemon
might atomically replace individual subprograms at run-time with newer versions to alter overall
program behavior, for instance, if global policies change.
eBPF programs
The BPF_PROG_LOAD command is used to load an eBPF program into the kernel. The return value for this
command is a new file descriptor associated with this eBPF program.
char bpf_log_buf[LOG_BUF_SIZE];
int
bpf_prog_load(enum bpf_prog_type type,
const struct bpf_insn *insns, int insn_cnt,
const char *license)
{
union bpf_attr attr = {
.prog_type = type,
.insns = ptr_to_u64(insns),
.insn_cnt = insn_cnt,
.license = ptr_to_u64(license),
.log_buf = ptr_to_u64(bpf_log_buf),
.log_size = LOG_BUF_SIZE,
.log_level = 1,
};
return bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
}
prog_type is one of the available program types:
enum bpf_prog_type {
BPF_PROG_TYPE_UNSPEC, /* Reserve 0 as invalid
program type */
BPF_PROG_TYPE_SOCKET_FILTER,
BPF_PROG_TYPE_KPROBE,
BPF_PROG_TYPE_SCHED_CLS,
BPF_PROG_TYPE_SCHED_ACT,
BPF_PROG_TYPE_TRACEPOINT,
BPF_PROG_TYPE_XDP,
BPF_PROG_TYPE_PERF_EVENT,
BPF_PROG_TYPE_CGROUP_SKB,
BPF_PROG_TYPE_CGROUP_SOCK,
BPF_PROG_TYPE_LWT_IN,
BPF_PROG_TYPE_LWT_OUT,
BPF_PROG_TYPE_LWT_XMIT,
BPF_PROG_TYPE_SOCK_OPS,
BPF_PROG_TYPE_SK_SKB,
BPF_PROG_TYPE_CGROUP_DEVICE,
BPF_PROG_TYPE_SK_MSG,
BPF_PROG_TYPE_RAW_TRACEPOINT,
BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
BPF_PROG_TYPE_LWT_SEG6LOCAL,
BPF_PROG_TYPE_LIRC_MODE2,
BPF_PROG_TYPE_SK_REUSEPORT,
BPF_PROG_TYPE_FLOW_DISSECTOR,
/* See /usr/include/linux/bpf.h for the full list. */
};
For further details of eBPF program types, see below.
The remaining fields of bpf_attr are set as follows:
• insns is an array of struct bpf_insn instructions.
• insn_cnt is the number of instructions in the program referred to by insns.
• license is a license string, which must be GPL compatible to call helper functions marked gpl_only.
(The licensing rules are the same as for kernel modules, so that also dual licenses, such as "Dual
BSD/GPL", may be used.)
• log_buf is a pointer to a caller-allocated buffer in which the in-kernel verifier can store the
verification log. This log is a multi-line string that can be checked by the program author in order
to understand how the verifier came to the conclusion that the eBPF program is unsafe. The format of
the output can change at any time as the verifier evolves.
• log_size size of the buffer pointed to by log_buf. If the size of the buffer is not large enough to
store all verifier messages, -1 is returned and errno is set to ENOSPC.
• log_level verbosity level of the verifier. A value of zero means that the verifier will not provide a
log; in this case, log_buf must be a null pointer, and log_size must be zero.
Applying close(2) to the file descriptor returned by BPF_PROG_LOAD will unload the eBPF program (but see
NOTES).
Maps are accessible from eBPF programs and are used to exchange data between eBPF programs and between
eBPF programs and user-space programs. For example, eBPF programs can process various events (like
kprobe, packets) and store their data into a map, and user-space programs can then fetch data from the
map. Conversely, user-space programs can use a map as a configuration mechanism, populating the map with
values checked by the eBPF program, which then modifies its behavior on the fly according to those
values.
eBPF program types
The eBPF program type (prog_type) determines the subset of kernel helper functions that the program may
call. The program type also determines the program input (context)—the format of struct bpf_context
(which is the data blob passed into the eBPF program as the first argument).
For example, a tracing program does not have the exact same subset of helper functions as a socket filter
program (though they may have some helpers in common). Similarly, the input (context) for a tracing
program is a set of register values, while for a socket filter it is a network packet.
The set of functions available to eBPF programs of a given type may increase in the future.
The following program types are supported:
BPF_PROG_TYPE_SOCKET_FILTER (since Linux 3.19)
Currently, the set of functions for BPF_PROG_TYPE_SOCKET_FILTER is:
bpf_map_lookup_elem(map_fd, void *key)
/* look up key in a map_fd */
bpf_map_update_elem(map_fd, void *key, void *value)
/* update key/value */
bpf_map_delete_elem(map_fd, void *key)
/* delete key in a map_fd */
The bpf_context argument is a pointer to a struct __sk_buff.
BPF_PROG_TYPE_KPROBE (since Linux 4.1)
[To be documented]
BPF_PROG_TYPE_SCHED_CLS (since Linux 4.1)
[To be documented]
BPF_PROG_TYPE_SCHED_ACT (since Linux 4.1)
[To be documented]
Events
Once a program is loaded, it can be attached to an event. Various kernel subsystems have different ways
to do so.
Since Linux 3.19, the following call will attach the program prog_fd to the socket sockfd, which was
created by an earlier call to socket(2):
setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_BPF,
&prog_fd, sizeof(prog_fd));
Since Linux 4.1, the following call may be used to attach the eBPF program referred to by the file
descriptor prog_fd to a perf event file descriptor, event_fd, that was created by a previous call to
perf_event_open(2):
ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
RETURN VALUE
For a successful call, the return value depends on the operation:
BPF_MAP_CREATE
The new file descriptor associated with the eBPF map.
BPF_PROG_LOAD
The new file descriptor associated with the eBPF program.
All other commands
Zero.
On error, -1 is returned, and errno is set to indicate the error.
ERRORS
E2BIG The eBPF program is too large or a map reached the max_entries limit (maximum number of elements).
EACCES For BPF_PROG_LOAD, even though all program instructions are valid, the program has been rejected
because it was deemed unsafe. This may be because it may have accessed a disallowed memory region
or an uninitialized stack/register or because the function constraints don't match the actual
types or because there was a misaligned memory access. In this case, it is recommended to call
bpf() again with log_level = 1 and examine log_buf for the specific reason provided by the
verifier.
EAGAIN For BPF_PROG_LOAD, indicates that needed resources are blocked. This happens when the verifier
detects pending signals while it is checking the validity of the bpf program. In this case, just
call bpf() again with the same parameters.
EBADF fd is not an open file descriptor.
EFAULT One of the pointers (key or value or log_buf or insns) is outside the accessible address space.
EINVAL The value specified in cmd is not recognized by this kernel.
EINVAL For BPF_MAP_CREATE, either map_type or attributes are invalid.
EINVAL For BPF_MAP_*_ELEM commands, some of the fields of union bpf_attr that are not used by this
command are not set to zero.
EINVAL For BPF_PROG_LOAD, indicates an attempt to load an invalid program. eBPF programs can be deemed
invalid due to unrecognized instructions, the use of reserved fields, jumps out of range, infinite
loops or calls of unknown functions.
ENOENT For BPF_MAP_LOOKUP_ELEM or BPF_MAP_DELETE_ELEM, indicates that the element with the given key was
not found.
ENOMEM Cannot allocate sufficient memory.
EPERM The call was made without sufficient privilege (without the CAP_SYS_ADMIN capability).
STANDARDS
Linux.
HISTORY
Linux 3.18.
NOTES
Prior to Linux 4.4, all bpf() commands require the caller to have the CAP_SYS_ADMIN capability. From
Linux 4.4 onwards, an unprivileged user may create limited programs of type BPF_PROG_TYPE_SOCKET_FILTER
and associated maps. However they may not store kernel pointers within the maps and are presently
limited to the following helper functions:
• get_random
• get_smp_processor_id
• tail_call
• ktime_get_ns
Unprivileged access may be blocked by writing the value 1 to the file
/proc/sys/kernel/unprivileged_bpf_disabled.
eBPF objects (maps and programs) can be shared between processes. For example, after fork(2), the child
inherits file descriptors referring to the same eBPF objects. In addition, file descriptors referring to
eBPF objects can be transferred over UNIX domain sockets. File descriptors referring to eBPF objects can
be duplicated in the usual way, using dup(2) and similar calls. An eBPF object is deallocated only after
all file descriptors referring to the object have been closed.
eBPF programs can be written in a restricted C that is compiled (using the clang compiler) into eBPF
bytecode. Various features are omitted from this restricted C, such as loops, global variables, variadic
functions, floating-point numbers, and passing structures as function arguments. Some examples can be
found in the samples/bpf/*_kern.c files in the kernel source tree.
The kernel contains a just-in-time (JIT) compiler that translates eBPF bytecode into native machine code
for better performance. Before Linux 4.15, the JIT compiler is disabled by default, but its operation
can be controlled by writing one of the following integer strings to the file
/proc/sys/net/core/bpf_jit_enable:
0 Disable JIT compilation (default).
1 Normal compilation.
2 Debugging mode. The generated opcodes are dumped in hexadecimal into the kernel log. These
opcodes can then be disassembled using the program tools/net/bpf_jit_disasm.c provided in the
kernel source tree.
Since Linux 4.15, the kernel may be configured with the CONFIG_BPF_JIT_ALWAYS_ON option. In this case,
the JIT compiler is always enabled, and the bpf_jit_enable is initialized to 1 and is immutable. (This
kernel configuration option was provided as a mitigation for one of the Spectre attacks against the BPF
interpreter.)
The JIT compiler for eBPF is currently available for the following architectures:
• x86-64 (since Linux 3.18; cBPF since Linux 3.0);
• ARM32 (since Linux 3.18; cBPF since Linux 3.4);
• SPARC 32 (since Linux 3.18; cBPF since Linux 3.5);
• ARM-64 (since Linux 3.18);
• s390 (since Linux 4.1; cBPF since Linux 3.7);
• PowerPC 64 (since Linux 4.8; cBPF since Linux 3.1);
• SPARC 64 (since Linux 4.12);
• x86-32 (since Linux 4.18);
• MIPS 64 (since Linux 4.18; cBPF since Linux 3.16);
• riscv (since Linux 5.1).
EXAMPLES
/* bpf+sockets example:
* 1. create array map of 256 elements
* 2. load program that counts number of packets received
* r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)]
* map[r0]++
* 3. attach prog_fd to raw socket via setsockopt()
* 4. print number of received TCP/UDP packets every second
*/
int
main(int argc, char *argv[])
{
int sock, map_fd, prog_fd, key;
long long value = 0, tcp_cnt, udp_cnt;
map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key),
sizeof(value), 256);
if (map_fd < 0) {
printf("failed to create map '%s'\n", strerror(errno));
/* likely not run as root */
return 1;
}
struct bpf_insn prog[] = {
BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), /* r6 = r1 */
BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol)),
/* r0 = ip->proto */
BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4),
/* *(u32 *)(fp - 4) = r0 */
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), /* r2 = fp */
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = r2 - 4 */
BPF_LD_MAP_FD(BPF_REG_1, map_fd), /* r1 = map_fd */
BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem),
/* r0 = map_lookup(r1, r2) */
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
/* if (r0 == 0) goto pc+2 */
BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
BPF_XADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0),
/* lock *(u64 *) r0 += r1 */
BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
BPF_EXIT_INSN(), /* return r0 */
};
prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
sizeof(prog) / sizeof(prog[0]), "GPL");
sock = open_raw_sock("lo");
assert(setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
sizeof(prog_fd)) == 0);
for (;;) {
key = IPPROTO_TCP;
assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
key = IPPROTO_UDP;
assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0);
printf("TCP %lld UDP %lld packets\n", tcp_cnt, udp_cnt);
sleep(1);
}
return 0;
}
Some complete working code can be found in the samples/bpf directory in the kernel source tree.
SEE ALSO
seccomp(2), bpf-helpers(7), socket(7), tc(8), tc-bpf(8)
Both classic and extended BPF are explained in the kernel source file
Documentation/networking/filter.txt.