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diff --git a/Documentation/bpf/map_sockmap.rst b/Documentation/bpf/map_sockmap.rst new file mode 100644 index 000000000000..cc92047c6630 --- /dev/null +++ b/Documentation/bpf/map_sockmap.rst @@ -0,0 +1,498 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright Red Hat + +============================================== +BPF_MAP_TYPE_SOCKMAP and BPF_MAP_TYPE_SOCKHASH +============================================== + +.. note:: + - ``BPF_MAP_TYPE_SOCKMAP`` was introduced in kernel version 4.14 + - ``BPF_MAP_TYPE_SOCKHASH`` was introduced in kernel version 4.18 + +``BPF_MAP_TYPE_SOCKMAP`` and ``BPF_MAP_TYPE_SOCKHASH`` maps can be used to +redirect skbs between sockets or to apply policy at the socket level based on +the result of a BPF (verdict) program with the help of the BPF helpers +``bpf_sk_redirect_map()``, ``bpf_sk_redirect_hash()``, +``bpf_msg_redirect_map()`` and ``bpf_msg_redirect_hash()``. + +``BPF_MAP_TYPE_SOCKMAP`` is backed by an array that uses an integer key as the +index to look up a reference to a ``struct sock``. The map values are socket +descriptors. Similarly, ``BPF_MAP_TYPE_SOCKHASH`` is a hash backed BPF map that +holds references to sockets via their socket descriptors. + +.. note:: + The value type is either __u32 or __u64; the latter (__u64) is to support + returning socket cookies to userspace. Returning the ``struct sock *`` that + the map holds to user-space is neither safe nor useful. + +These maps may have BPF programs attached to them, specifically a parser program +and a verdict program. The parser program determines how much data has been +parsed and therefore how much data needs to be queued to come to a verdict. The +verdict program is essentially the redirect program and can return a verdict +of ``__SK_DROP``, ``__SK_PASS``, or ``__SK_REDIRECT``. + +When a socket is inserted into one of these maps, its socket callbacks are +replaced and a ``struct sk_psock`` is attached to it. Additionally, this +``sk_psock`` inherits the programs that are attached to the map. + +A sock object may be in multiple maps, but can only inherit a single +parse or verdict program. If adding a sock object to a map would result +in having multiple parser programs the update will return an EBUSY error. + +The supported programs to attach to these maps are: + +.. code-block:: c + + struct sk_psock_progs { + struct bpf_prog *msg_parser; + struct bpf_prog *stream_parser; + struct bpf_prog *stream_verdict; + struct bpf_prog *skb_verdict; + }; + +.. note:: + Users are not allowed to attach ``stream_verdict`` and ``skb_verdict`` + programs to the same map. + +The attach types for the map programs are: + +- ``msg_parser`` program - ``BPF_SK_MSG_VERDICT``. +- ``stream_parser`` program - ``BPF_SK_SKB_STREAM_PARSER``. +- ``stream_verdict`` program - ``BPF_SK_SKB_STREAM_VERDICT``. +- ``skb_verdict`` program - ``BPF_SK_SKB_VERDICT``. + +There are additional helpers available to use with the parser and verdict +programs: ``bpf_msg_apply_bytes()`` and ``bpf_msg_cork_bytes()``. With +``bpf_msg_apply_bytes()`` BPF programs can tell the infrastructure how many +bytes the given verdict should apply to. The helper ``bpf_msg_cork_bytes()`` +handles a different case where a BPF program cannot reach a verdict on a msg +until it receives more bytes AND the program doesn't want to forward the packet +until it is known to be good. + +Finally, the helpers ``bpf_msg_pull_data()`` and ``bpf_msg_push_data()`` are +available to ``BPF_PROG_TYPE_SK_MSG`` BPF programs to pull in data and set the +start and end pointers to given values or to add metadata to the ``struct +sk_msg_buff *msg``. + +All these helpers will be described in more detail below. + +Usage +===== +Kernel BPF +---------- +bpf_msg_redirect_map() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map *map, u32 key, u64 flags) + +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 BPF 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 select the ingress path otherwise the egress path is selected. This is the +only flag supported for now. + +Returns ``SK_PASS`` on success, or ``SK_DROP`` on error. + +bpf_sk_redirect_map() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key u64 flags) + +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 select the ingress path otherwise the egress path is selected. This is the +only flag supported for now. + +Returns ``SK_PASS`` on success, or ``SK_DROP`` on error. + +bpf_map_lookup_elem() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + void *bpf_map_lookup_elem(struct bpf_map *map, const void *key) + +socket entries of type ``struct sock *`` can be retrieved using the +``bpf_map_lookup_elem()`` helper. + +bpf_sock_map_update() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags) + +Add an entry to, or update a ``map`` referencing sockets. The ``skops`` is used +as a new value for the entry associated to ``key``. The ``flags`` argument can +be 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. + +If the ``map`` has BPF programs (parser and verdict), those will be inherited +by the socket being added. If the socket is already attached to BPF programs, +this results in an error. + +Returns 0 on success, or a negative error in case of failure. + +bpf_sock_hash_update() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags) + +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``. + +The ``flags`` argument can be 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. + +If the ``map`` has BPF programs (parser and verdict), those will be inherited +by the socket being added. If the socket is already attached to BPF programs, +this results in an error. + +Returns 0 on success, or a negative error in case of failure. + +bpf_msg_redirect_hash() +^^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map *map, void *key, u64 flags) + +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 BPF 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 select the ingress path otherwise the egress path is +selected. This is the only flag supported for now. + +Returns ``SK_PASS`` on success, or ``SK_DROP`` on error. + +bpf_sk_redirect_hash() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map, void *key, u64 flags) + +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 BPF 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 select the ingress path otherwise the egress path is +selected. This is the only flag supported for now. + +Returns ``SK_PASS`` on success, or ``SK_DROP`` on error. + +bpf_msg_apply_bytes() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes) + +For socket policies, apply the verdict of the BPF program to the next (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 BPF program is supposed to read and for which it + should apply a verdict. +- A BPF program only cares to read the first ``bytes`` of a ``msg``. If the + message has a large payload, then setting up and calling the BPF program + repeatedly for all bytes, even though the verdict is already known, would + create unnecessary overhead. + +Returns 0 + +bpf_msg_cork_bytes() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes) + +For socket policies, prevent the execution of the verdict BPF program for +message ``msg`` until the number of ``bytes`` 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. + +Returns 0 + +bpf_msg_pull_data() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64 flags) + +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) BPF verdict is being decided. This helper can be used to pull in data +and to set the start and end pointers 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. + +Returns 0 on success, or a negative error in case of failure. + +bpf_map_lookup_elem() +^^^^^^^^^^^^^^^^^^^^^ + +.. code-block:: c + + void *bpf_map_lookup_elem(struct bpf_map *map, const void *key) + +Look up a socket entry in the sockmap or sockhash map. + +Returns the socket entry associated to ``key``, or NULL if no entry was found. + +bpf_map_update_elem() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags) + +Add or update a socket entry in a sockmap or sockhash. + +The flags argument can be 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. + +Returns 0 on success, or a negative error in case of failure. + +bpf_map_delete_elem() +^^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + long bpf_map_delete_elem(struct bpf_map *map, const void *key) + +Delete a socket entry from a sockmap or a sockhash. + +Returns 0 on success, or a negative error in case of failure. + +User space +---------- +bpf_map_update_elem() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + int bpf_map_update_elem(int fd, const void *key, const void *value, __u64 flags) + +Sockmap entries can be added or updated using the ``bpf_map_update_elem()`` +function. The ``key`` parameter is the index value of the sockmap array. And the +``value`` parameter is the FD value of that socket. + +Under the hood, the sockmap update function uses the socket FD value to +retrieve the associated socket and its attached psock. + +The flags argument can be 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. + +bpf_map_lookup_elem() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + int bpf_map_lookup_elem(int fd, const void *key, void *value) + +Sockmap entries can be retrieved using the ``bpf_map_lookup_elem()`` function. + +.. note:: + The entry returned is a socket cookie rather than a socket itself. + +bpf_map_delete_elem() +^^^^^^^^^^^^^^^^^^^^^ +.. code-block:: c + + int bpf_map_delete_elem(int fd, const void *key) + +Sockmap entries can be deleted using the ``bpf_map_delete_elem()`` +function. + +Returns 0 on success, or negative error in case of failure. + +Examples +======== + +Kernel BPF +---------- +Several examples of the use of sockmap APIs can be found in: + +- `tools/testing/selftests/bpf/progs/test_sockmap_kern.h`_ +- `tools/testing/selftests/bpf/progs/sockmap_parse_prog.c`_ +- `tools/testing/selftests/bpf/progs/sockmap_verdict_prog.c`_ +- `tools/testing/selftests/bpf/progs/test_sockmap_listen.c`_ +- `tools/testing/selftests/bpf/progs/test_sockmap_update.c`_ + +The following code snippet shows how to declare a sockmap. + +.. code-block:: c + + struct { + __uint(type, BPF_MAP_TYPE_SOCKMAP); + __uint(max_entries, 1); + __type(key, __u32); + __type(value, __u64); + } sock_map_rx SEC(".maps"); + +The following code snippet shows a sample parser program. + +.. code-block:: c + + SEC("sk_skb/stream_parser") + int bpf_prog_parser(struct __sk_buff *skb) + { + return skb->len; + } + +The following code snippet shows a simple verdict program that interacts with a +sockmap to redirect traffic to another socket based on the local port. + +.. code-block:: c + + SEC("sk_skb/stream_verdict") + int bpf_prog_verdict(struct __sk_buff *skb) + { + __u32 lport = skb->local_port; + __u32 idx = 0; + + if (lport == 10000) + return bpf_sk_redirect_map(skb, &sock_map_rx, idx, 0); + + return SK_PASS; + } + +The following code snippet shows how to declare a sockhash map. + +.. code-block:: c + + struct socket_key { + __u32 src_ip; + __u32 dst_ip; + __u32 src_port; + __u32 dst_port; + }; + + struct { + __uint(type, BPF_MAP_TYPE_SOCKHASH); + __uint(max_entries, 1); + __type(key, struct socket_key); + __type(value, __u64); + } sock_hash_rx SEC(".maps"); + +The following code snippet shows a simple verdict program that interacts with a +sockhash to redirect traffic to another socket based on a hash of some of the +skb parameters. + +.. code-block:: c + + static inline + void extract_socket_key(struct __sk_buff *skb, struct socket_key *key) + { + key->src_ip = skb->remote_ip4; + key->dst_ip = skb->local_ip4; + key->src_port = skb->remote_port >> 16; + key->dst_port = (bpf_htonl(skb->local_port)) >> 16; + } + + SEC("sk_skb/stream_verdict") + int bpf_prog_verdict(struct __sk_buff *skb) + { + struct socket_key key; + + extract_socket_key(skb, &key); + + return bpf_sk_redirect_hash(skb, &sock_hash_rx, &key, 0); + } + +User space +---------- +Several examples of the use of sockmap APIs can be found in: + +- `tools/testing/selftests/bpf/prog_tests/sockmap_basic.c`_ +- `tools/testing/selftests/bpf/test_sockmap.c`_ +- `tools/testing/selftests/bpf/test_maps.c`_ + +The following code sample shows how to create a sockmap, attach a parser and +verdict program, as well as add a socket entry. + +.. code-block:: c + + int create_sample_sockmap(int sock, int parse_prog_fd, int verdict_prog_fd) + { + int index = 0; + int map, err; + + map = bpf_map_create(BPF_MAP_TYPE_SOCKMAP, NULL, sizeof(int), sizeof(int), 1, NULL); + if (map < 0) { + fprintf(stderr, "Failed to create sockmap: %s\n", strerror(errno)); + return -1; + } + + err = bpf_prog_attach(parse_prog_fd, map, BPF_SK_SKB_STREAM_PARSER, 0); + if (err){ + fprintf(stderr, "Failed to attach_parser_prog_to_map: %s\n", strerror(errno)); + goto out; + } + + err = bpf_prog_attach(verdict_prog_fd, map, BPF_SK_SKB_STREAM_VERDICT, 0); + if (err){ + fprintf(stderr, "Failed to attach_verdict_prog_to_map: %s\n", strerror(errno)); + goto out; + } + + err = bpf_map_update_elem(map, &index, &sock, BPF_NOEXIST); + if (err) { + fprintf(stderr, "Failed to update sockmap: %s\n", strerror(errno)); + goto out; + } + + out: + close(map); + return err; + } + +References +=========== + +- https://github.com/jrfastab/linux-kernel-xdp/commit/c89fd73cb9d2d7f3c716c3e00836f07b1aeb261f +- https://lwn.net/Articles/731133/ +- http://vger.kernel.org/lpc_net2018_talks/ktls_bpf_paper.pdf +- https://lwn.net/Articles/748628/ +- https://lore.kernel.org/bpf/20200218171023.844439-7-jakub@cloudflare.com/ + +.. _`tools/testing/selftests/bpf/progs/test_sockmap_kern.h`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/progs/test_sockmap_kern.h +.. _`tools/testing/selftests/bpf/progs/sockmap_parse_prog.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/progs/sockmap_parse_prog.c +.. _`tools/testing/selftests/bpf/progs/sockmap_verdict_prog.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/progs/sockmap_verdict_prog.c +.. _`tools/testing/selftests/bpf/prog_tests/sockmap_basic.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c +.. _`tools/testing/selftests/bpf/test_sockmap.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/test_sockmap.c +.. _`tools/testing/selftests/bpf/test_maps.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/test_maps.c +.. _`tools/testing/selftests/bpf/progs/test_sockmap_listen.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/progs/test_sockmap_listen.c +.. _`tools/testing/selftests/bpf/progs/test_sockmap_update.c`: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/progs/test_sockmap_update.c |