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diff --git a/man2/bpf.2 b/man2/bpf.2 new file mode 100644 index 0000000..4df108d --- /dev/null +++ b/man2/bpf.2 @@ -0,0 +1,1273 @@ +.\" Copyright (C) 2015 Alexei Starovoitov <ast@kernel.org> +.\" and Copyright (C) 2015 Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH bpf 2 2023-07-28 "Linux man-pages 6.05.01" +.SH NAME +bpf \- perform a command on an extended BPF map or program +.SH SYNOPSIS +.nf +.B #include <linux/bpf.h> +.PP +.BI "int bpf(int " cmd ", union bpf_attr *" attr ", unsigned int " size ); +.fi +.SH DESCRIPTION +The +.BR 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. +.PP +eBPF extends cBPF in multiple ways, including the ability to call +a fixed set of in-kernel helper functions +.\" See 'enum bpf_func_id' in include/uapi/linux/bpf.h +(via the +.B BPF_CALL +opcode extension provided by eBPF) +and access shared data structures such as eBPF maps. +.\" +.SS 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. +.PP +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. +.PP +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, +.\" Defined by the kernel constant MAX_TAIL_CALL_CNT in include/linux/bpf.h +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 +.BR bpf (). +If a map lookup fails, the current program continues its execution. +See +.B BPF_MAP_TYPE_PROG_ARRAY +below for further details. +.PP +Generally, eBPF programs are loaded by the user process and automatically +unloaded when the process exits. +In some cases, for example, +.BR 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 +.BR bpf (). +.PP +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. +.PP +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 +.BR 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. +.PP +The same eBPF program can be attached to multiple events and different +eBPF programs can access the same map: +.PP +.in +4n +.EX +tracing tracing tracing packet packet packet +event A event B event C on eth0 on eth1 on eth2 + | | | | | \[ha] + | | | | 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 |\-\- +.EE +.in +.\" +.SS Arguments +The operation to be performed by the +.BR bpf () +system call is determined by the +.I cmd +argument. +Each operation takes an accompanying argument, +provided via +.IR attr , +which is a pointer to a union of type +.I bpf_attr +(see below). +The unused fields and padding must be zeroed out before the call. +The +.I size +argument is the size of the union pointed to by +.IR attr . +.PP +The value provided in +.I cmd +is one of the following: +.TP +.B BPF_MAP_CREATE +Create a map and return a file descriptor that refers to the map. +The close-on-exec file descriptor flag (see +.BR fcntl (2)) +is automatically enabled for the new file descriptor. +.TP +.B BPF_MAP_LOOKUP_ELEM +Look up an element by key in a specified map and return its value. +.TP +.B BPF_MAP_UPDATE_ELEM +Create or update an element (key/value pair) in a specified map. +.TP +.B BPF_MAP_DELETE_ELEM +Look up and delete an element by key in a specified map. +.TP +.B BPF_MAP_GET_NEXT_KEY +Look up an element by key in a specified map and return the key +of the next element. +.TP +.B 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 +.BR fcntl (2)) +is automatically enabled for the new file descriptor. +.IP +The +.I bpf_attr +union consists of various anonymous structures that are used by different +.BR bpf () +commands: +.PP +.in +4n +.EX +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; /* \[aq]const struct bpf_insn *\[aq] */ + __aligned_u64 license; /* \[aq]const char *\[aq] */ + __u32 log_level; /* verbosity level of verifier */ + __u32 log_size; /* size of user buffer */ + __aligned_u64 log_buf; /* user supplied \[aq]char *\[aq] + buffer */ + __u32 kern_version; + /* checked when prog_type=kprobe + (since Linux 4.1) */ +.\" commit 2541517c32be2531e0da59dfd7efc1ce844644f5 + }; +} __attribute__((aligned(8))); +.EE +.in +.\" +.SS 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. +.PP +Each map type has the following attributes: +.IP \[bu] 3 +type +.IP \[bu] +maximum number of elements +.IP \[bu] +key size in bytes +.IP \[bu] +value size in bytes +.PP +The following wrapper functions demonstrate how various +.BR bpf () +commands can be used to access the maps. +The functions use the +.I cmd +argument to invoke different operations. +.TP +.B BPF_MAP_CREATE +The +.B BPF_MAP_CREATE +command creates a new map, +returning a new file descriptor that refers to the map. +.IP +.in +4n +.EX +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)); +} +.EE +.in +.IP +The new map has the type specified by +.IR map_type , +and attributes as specified in +.IR key_size , +.IR value_size , +and +.IR max_entries . +On success, this operation returns a file descriptor. +On error, \-1 is returned and +.I errno +is set to +.BR EINVAL , +.BR EPERM , +or +.BR ENOMEM . +.IP +The +.I key_size +and +.I value_size +attributes will be used by the verifier during program loading +to check that the program is calling +.BR bpf_map_*_elem () +helper functions with a correctly initialized +.I key +and to check that the program doesn't access the map element +.I value +beyond the specified +.IR value_size . +For example, when a map is created with a +.I key_size +of 8 and the eBPF program calls +.IP +.in +4n +.EX +bpf_map_lookup_elem(map_fd, fp \- 4) +.EE +.in +.IP +the program will be rejected, +since the in-kernel helper function +.IP +.in +4n +.EX +bpf_map_lookup_elem(map_fd, void *key) +.EE +.in +.IP +expects to read 8 bytes from the location pointed to by +.IR key , +but the +.I fp\ \-\ 4 +(where +.I fp +is the top of the stack) +starting address will cause out-of-bounds stack access. +.IP +Similarly, when a map is created with a +.I value_size +of 1 and the eBPF program contains +.IP +.in +4n +.EX +value = bpf_map_lookup_elem(...); +*(u32 *) value = 1; +.EE +.in +.IP +the program will be rejected, since it accesses the +.I value +pointer beyond the specified 1 byte +.I value_size +limit. +.IP +Currently, the following values are supported for +.IR map_type : +.IP +.in +4n +.EX +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. */ +}; +.EE +.in +.IP +.I map_type +selects one of the available map implementations in the kernel. +.\" FIXME We need an explanation of why one might choose each of +.\" these map implementations +For all map types, +eBPF programs access maps with the same +.BR bpf_map_lookup_elem () +and +.BR bpf_map_update_elem () +helper functions. +Further details of the various map types are given below. +.TP +.B BPF_MAP_LOOKUP_ELEM +The +.B BPF_MAP_LOOKUP_ELEM +command looks up an element with a given +.I key +in the map referred to by the file descriptor +.IR fd . +.IP +.in +4n +.EX +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)); +} +.EE +.in +.IP +If an element is found, +the operation returns zero and stores the element's value into +.IR value , +which must point to a buffer of +.I value_size +bytes. +.IP +If no element is found, the operation returns \-1 and sets +.I errno +to +.BR ENOENT . +.TP +.B BPF_MAP_UPDATE_ELEM +The +.B BPF_MAP_UPDATE_ELEM +command +creates or updates an element with a given +.I key/value +in the map referred to by the file descriptor +.IR fd . +.IP +.in +4n +.EX +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)); +} +.EE +.in +.IP +The +.I flags +argument should be specified as one of the following: +.RS +.TP +.B BPF_ANY +Create a new element or update an existing element. +.TP +.B BPF_NOEXIST +Create a new element only if it did not exist. +.TP +.B BPF_EXIST +Update an existing element. +.RE +.IP +On success, the operation returns zero. +On error, \-1 is returned and +.I errno +is set to +.BR EINVAL , +.BR EPERM , +.BR ENOMEM , +or +.BR E2BIG . +.B E2BIG +indicates that the number of elements in the map reached the +.I max_entries +limit specified at map creation time. +.B EEXIST +will be returned if +.I flags +specifies +.B BPF_NOEXIST +and the element with +.I key +already exists in the map. +.B ENOENT +will be returned if +.I flags +specifies +.B BPF_EXIST +and the element with +.I key +doesn't exist in the map. +.TP +.B BPF_MAP_DELETE_ELEM +The +.B BPF_MAP_DELETE_ELEM +command +deletes the element whose key is +.I key +from the map referred to by the file descriptor +.IR fd . +.IP +.in +4n +.EX +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)); +} +.EE +.in +.IP +On success, zero is returned. +If the element is not found, \-1 is returned and +.I errno +is set to +.BR ENOENT . +.TP +.B BPF_MAP_GET_NEXT_KEY +The +.B BPF_MAP_GET_NEXT_KEY +command looks up an element by +.I key +in the map referred to by the file descriptor +.I fd +and sets the +.I next_key +pointer to the key of the next element. +.IP +.in +4n +.EX +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)); +} +.EE +.in +.IP +If +.I key +is found, the operation returns zero and sets the +.I next_key +pointer to the key of the next element. +If +.I key +is not found, the operation returns zero and sets the +.I next_key +pointer to the key of the first element. +If +.I key +is the last element, \-1 is returned and +.I errno +is set to +.BR ENOENT . +Other possible +.I errno +values are +.BR ENOMEM , +.BR EFAULT , +.BR EPERM , +and +.BR EINVAL . +This method can be used to iterate over all elements in the map. +.TP +.B close(map_fd) +Delete the map referred to by the file descriptor +.IR map_fd . +When the user-space program that created a map exits, all maps will +be deleted automatically (but see NOTES). +.\" +.SS eBPF map types +The following map types are supported: +.TP +.B BPF_MAP_TYPE_HASH +.\" commit 0f8e4bd8a1fc8c4185f1630061d0a1f2d197a475 +Hash-table maps have the following characteristics: +.RS +.IP \[bu] 3 +Maps are created and destroyed by user-space programs. +Both user-space and eBPF programs +can perform lookup, update, and delete operations. +.IP \[bu] +The kernel takes care of allocating and freeing key/value pairs. +.IP \[bu] +The +.BR map_update_elem () +helper will fail to insert new element when the +.I max_entries +limit is reached. +(This ensures that eBPF programs cannot exhaust memory.) +.IP \[bu] +.BR map_update_elem () +replaces existing elements atomically. +.RE +.IP +Hash-table maps are +optimized for speed of lookup. +.TP +.B BPF_MAP_TYPE_ARRAY +.\" commit 28fbcfa08d8ed7c5a50d41a0433aad222835e8e3 +Array maps have the following characteristics: +.RS +.IP \[bu] 3 +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 +.I value_size +are constant for the life of the eBPF program. +In other words, +.BR array_map_lookup_elem () +may be 'inlined' by the verifier/JIT compiler +while preserving concurrent access to this map from user space. +.IP \[bu] +All array elements pre-allocated and zero initialized at init time +.IP \[bu] +The key is an array index, and must be exactly four bytes. +.IP \[bu] +.BR map_delete_elem () +fails with the error +.BR EINVAL , +since elements cannot be deleted. +.IP \[bu] +.BR map_update_elem () +replaces elements in a +.B 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 +.B __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. +.RE +.IP +Among the uses for array maps are the following: +.RS +.IP \[bu] 3 +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. +.IP \[bu] +Aggregation of tracing events into a fixed set of buckets. +.IP \[bu] +Accounting of networking events, for example, number of packets and packet +sizes. +.RE +.TP +.BR 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 +.I key_size +and +.I value_size +must be exactly four bytes. +This map is used in conjunction with the +.BR bpf_tail_call () +helper. +.IP +This means that an eBPF program with a program array map attached to it +can call from kernel side into +.IP +.in +4n +.EX +void bpf_tail_call(void *context, void *prog_map, + unsigned int index); +.EE +.in +.IP +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. +.IP +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 +.\" MAX_TAIL_CALL_CNT +nested calls has been exceed), +execution continues with the current eBPF program. +This can be used as a fall-through for default cases. +.IP +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. +.\" +.SS eBPF programs +The +.B 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. +.PP +.in +4n +.EX +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)); +} +.EE +.in +.PP +.I prog_type +is one of the available program types: +.IP +.in +4n +.EX +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. */ +}; +.EE +.in +.PP +For further details of eBPF program types, see below. +.PP +The remaining fields of +.I bpf_attr +are set as follows: +.IP \[bu] 3 +.I insns +is an array of +.I "struct bpf_insn" +instructions. +.IP \[bu] +.I insn_cnt +is the number of instructions in the program referred to by +.IR insns . +.IP \[bu] +.I license +is a license string, which must be GPL compatible to call helper functions +marked +.IR 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.) +.IP \[bu] +.I 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. +.IP \[bu] +.I log_size +size of the buffer pointed to by +.IR log_buf . +If the size of the buffer is not large enough to store all +verifier messages, \-1 is returned and +.I errno +is set to +.BR ENOSPC . +.IP \[bu] +.I log_level +verbosity level of the verifier. +A value of zero means that the verifier will not provide a log; +in this case, +.I log_buf +must be a NULL pointer, and +.I log_size +must be zero. +.PP +Applying +.BR close (2) +to the file descriptor returned by +.B BPF_PROG_LOAD +will unload the eBPF program (but see NOTES). +.PP +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. +.\" +.\" +.SS eBPF program types +The eBPF program type +.RI ( prog_type ) +determines the subset of kernel helper functions that the program +may call. +The program type also determines the program input (context)\[em]the +format of +.I "struct bpf_context" +(which is the data blob passed into the eBPF program as the first argument). +.\" +.\" FIXME +.\" Somewhere in this page we need a general introduction to the +.\" bpf_context. For example, how does a BPF program access the +.\" context? +.PP +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. +.PP +The set of functions available to eBPF programs of a given type may increase +in the future. +.PP +The following program types are supported: +.TP +.BR BPF_PROG_TYPE_SOCKET_FILTER " (since Linux 3.19)" +Currently, the set of functions for +.B BPF_PROG_TYPE_SOCKET_FILTER +is: +.IP +.in +4n +.EX +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 */ +.EE +.in +.IP +The +.I bpf_context +argument is a pointer to a +.IR "struct __sk_buff" . +.\" FIXME: We need some text here to explain how the program +.\" accesses __sk_buff. +.\" See 'struct __sk_buff' and commit 9bac3d6d548e5 +.\" +.\" Alexei commented: +.\" Actually now in case of SOCKET_FILTER, SCHED_CLS, SCHED_ACT +.\" the program can now access skb fields. +.\" +.TP +.BR BPF_PROG_TYPE_KPROBE " (since Linux 4.1)" +.\" commit 2541517c32be2531e0da59dfd7efc1ce844644f5 +[To be documented] +.\" FIXME Document this program type +.\" Describe allowed helper functions for this program type +.\" Describe bpf_context for this program type +.\" +.\" FIXME We need text here to describe 'kern_version' +.TP +.BR BPF_PROG_TYPE_SCHED_CLS " (since Linux 4.1)" +.\" commit 96be4325f443dbbfeb37d2a157675ac0736531a1 +.\" commit e2e9b6541dd4b31848079da80fe2253daaafb549 +[To be documented] +.\" FIXME Document this program type +.\" Describe allowed helper functions for this program type +.\" Describe bpf_context for this program type +.TP +.BR BPF_PROG_TYPE_SCHED_ACT " (since Linux 4.1)" +.\" commit 94caee8c312d96522bcdae88791aaa9ebcd5f22c +.\" commit a8cb5f556b567974d75ea29c15181c445c541b1f +[To be documented] +.\" FIXME Document this program type +.\" Describe allowed helper functions for this program type +.\" Describe bpf_context for this program type +.SS Events +Once a program is loaded, it can be attached to an event. +Various kernel subsystems have different ways to do so. +.PP +Since Linux 3.19, +.\" commit 89aa075832b0da4402acebd698d0411dcc82d03e +the following call will attach the program +.I prog_fd +to the socket +.IR sockfd , +which was created by an earlier call to +.BR socket (2): +.PP +.in +4n +.EX +setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_BPF, + &prog_fd, sizeof(prog_fd)); +.EE +.in +.PP +Since Linux 4.1, +.\" commit 2541517c32be2531e0da59dfd7efc1ce844644f5 +the following call may be used to attach +the eBPF program referred to by the file descriptor +.I prog_fd +to a perf event file descriptor, +.IR event_fd , +that was created by a previous call to +.BR perf_event_open (2): +.PP +.in +4n +.EX +ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd); +.EE +.in +.\" +.\" +.SH RETURN VALUE +For a successful call, the return value depends on the operation: +.TP +.B BPF_MAP_CREATE +The new file descriptor associated with the eBPF map. +.TP +.B BPF_PROG_LOAD +The new file descriptor associated with the eBPF program. +.TP +All other commands +Zero. +.PP +On error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B E2BIG +The eBPF program is too large or a map reached the +.I max_entries +limit (maximum number of elements). +.TP +.B EACCES +For +.BR 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 +.BR bpf () +again with +.I log_level = 1 +and examine +.I log_buf +for the specific reason provided by the verifier. +.TP +.B EAGAIN +For +.BR 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 +.BR bpf () +again with the same parameters. +.TP +.B EBADF +.I fd +is not an open file descriptor. +.TP +.B EFAULT +One of the pointers +.RI ( key +or +.I value +or +.I log_buf +or +.IR insns ) +is outside the accessible address space. +.TP +.B EINVAL +The value specified in +.I cmd +is not recognized by this kernel. +.TP +.B EINVAL +For +.BR BPF_MAP_CREATE , +either +.I map_type +or attributes are invalid. +.TP +.B EINVAL +For +.B BPF_MAP_*_ELEM +commands, +some of the fields of +.I "union bpf_attr" +that are not used by this command +are not set to zero. +.TP +.B EINVAL +For +.BR 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. +.TP +.B ENOENT +For +.B BPF_MAP_LOOKUP_ELEM +or +.BR BPF_MAP_DELETE_ELEM , +indicates that the element with the given +.I key +was not found. +.TP +.B ENOMEM +Cannot allocate sufficient memory. +.TP +.B EPERM +The call was made without sufficient privilege +(without the +.B CAP_SYS_ADMIN +capability). +.SH STANDARDS +Linux. +.SH HISTORY +Linux 3.18. +.SH NOTES +Prior to Linux 4.4, all +.BR bpf () +commands require the caller to have the +.B CAP_SYS_ADMIN +capability. +From Linux 4.4 onwards, +.\" commit 1be7f75d1668d6296b80bf35dcf6762393530afc +an unprivileged user may create limited programs of type +.B 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: +.\" [Linux 5.6] mtk: The list of available functions is, I think, governed +.\" by the check in net/core/filter.c::bpf_base_func_proto(). +.IP \[bu] 3 +get_random +.PD 0 +.IP \[bu] +get_smp_processor_id +.IP \[bu] +tail_call +.IP \[bu] +ktime_get_ns +.PD +.PP +Unprivileged access may be blocked by writing the value 1 to the file +.IR /proc/sys/kernel/unprivileged_bpf_disabled . +.PP +eBPF objects (maps and programs) can be shared between processes. +For example, after +.BR 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 +.BR dup (2) +and similar calls. +An eBPF object is deallocated only after all file descriptors +referring to the object have been closed. +.PP +eBPF programs can be written in a restricted C that is compiled (using the +.B 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 +.I samples/bpf/*_kern.c +files in the kernel source tree. +.\" There are also examples for the tc classifier, in the iproute2 +.\" project, in examples/bpf +.PP +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 +.IR /proc/sys/net/core/bpf_jit_enable : +.TP +.B 0 +Disable JIT compilation (default). +.TP +.B 1 +Normal compilation. +.TP +.B 2 +Debugging mode. +The generated opcodes are dumped in hexadecimal into the kernel log. +These opcodes can then be disassembled using the program +.I tools/net/bpf_jit_disasm.c +provided in the kernel source tree. +.PP +Since Linux 4.15, +.\" commit 290af86629b25ffd1ed6232c4e9107da031705cb +the kernel may configured with the +.B CONFIG_BPF_JIT_ALWAYS_ON +option. +In this case, the JIT compiler is always enabled, and the +.I 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.) +.PP +The JIT compiler for eBPF is currently +.\" Last reviewed in Linux 4.18-rc by grepping for BPF_ALU64 in arch/ +.\" and by checking the documentation for bpf_jit_enable in +.\" Documentation/sysctl/net.txt +available for the following architectures: +.IP \[bu] 3 +x86-64 (since Linux 3.18; cBPF since Linux 3.0); +.\" commit 0a14842f5a3c0e88a1e59fac5c3025db39721f74 +.PD 0 +.IP \[bu] +ARM32 (since Linux 3.18; cBPF since Linux 3.4); +.\" commit ddecdfcea0ae891f782ae853771c867ab51024c2 +.IP \[bu] +SPARC 32 (since Linux 3.18; cBPF since Linux 3.5); +.\" commit 2809a2087cc44b55e4377d7b9be3f7f5d2569091 +.IP \[bu] +ARM-64 (since Linux 3.18); +.\" commit e54bcde3d69d40023ae77727213d14f920eb264a +.IP \[bu] +s390 (since Linux 4.1; cBPF since Linux 3.7); +.\" commit c10302efe569bfd646b4c22df29577a4595b4580 +.IP \[bu] +PowerPC 64 (since Linux 4.8; cBPF since Linux 3.1); +.\" commit 0ca87f05ba8bdc6791c14878464efc901ad71e99 +.\" commit 156d0e290e969caba25f1851c52417c14d141b24 +.IP \[bu] +SPARC 64 (since Linux 4.12); +.\" commit 7a12b5031c6b947cc13918237ae652b536243b76 +.IP \[bu] +x86-32 (since Linux 4.18); +.\" commit 03f5781be2c7b7e728d724ac70ba10799cc710d7 +.IP \[bu] +MIPS 64 (since Linux 4.18; cBPF since Linux 3.16); +.\" commit c6610de353da5ca6eee5b8960e838a87a90ead0c +.\" commit f381bf6d82f032b7410185b35d000ea370ac706b +.IP \[bu] +riscv (since Linux 5.1). +.\" commit 2353ecc6f91fd15b893fa01bf85a1c7a823ee4f2 +.PD +.SH EXAMPLES +.\" [[FIXME]] SRC BEGIN (bpf.c) +.EX +/* 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 \[aq]%s\[aq]\en", 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 */ +.\" == atomic64_add + 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\en", tcp_cnt, udp_cnt); + sleep(1); + } +\& + return 0; +} +.EE +.\" SRC END +.PP +Some complete working code can be found in the +.I samples/bpf +directory in the kernel source tree. +.SH SEE ALSO +.BR seccomp (2), +.BR bpf\-helpers (7), +.BR socket (7), +.BR tc (8), +.BR tc\-bpf (8) +.PP +Both classic and extended BPF are explained in the kernel source file +.IR Documentation/networking/filter.txt . |