mtahhan@xxxxxxxxxx writes: > From: Maryam Tahhan <mtahhan@xxxxxxxxxx> > > Add documentation for BPF_MAP_TYPE_SOCK[MAP|HASH] > including kernel versions introduced, usage > and examples. > > Signed-off-by: Maryam Tahhan <mtahhan@xxxxxxxxxx> > --- > Documentation/bpf/map_sockmap.rst | 439 ++++++++++++++++++++++++++++++ > 1 file changed, 439 insertions(+) > create mode 100644 Documentation/bpf/map_sockmap.rst > > diff --git a/Documentation/bpf/map_sockmap.rst b/Documentation/bpf/map_sockmap.rst > new file mode 100644 > index 000000000000..8824a67b24e8 > --- /dev/null > +++ b/Documentation/bpf/map_sockmap.rst > @@ -0,0 +1,439 @@ > +.. 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`` is backed by an array that uses an integer key as the > +index to lookup a reference to a sock struct. The map values are sockets. > +Similarly, ``BPF_MAP_TYPE_SOCKHASH`` is a hash backed BPF map that holds > +references to sockets. Should mention that value type must be sizeof(__u32) or sizeof(__u64). The reason for supporting __u64 seems to be to return socket cookies to userspace. Details here: https://lore.kernel.org/bpf/20200218171023.844439-7-jakub@xxxxxxxxxxxxxx/ > + > +When these maps are created BPF programs are attached to them. The list of > +allowed programs is shown below: > + > +.. 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 parser programs determine how much data needs to be queued to come to a > +verdict. The verdict programs return a verdict ``__SK_DROP``, ``__SK_PASS``, or > +``__SK_REDIRECT``. > + > +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``. > + > +These maps can be used to redirect skbs between sockets or to apply policy at > +the socket level based on the result of a 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()``. > + > +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. > + > +.. note:: > + For more details of the socket callbacks that get replaced please see: > + > + - TCP BPF functions: ``net/ipv4/tcp_bpf.c`` > + - UDP BPF functions: ``net/ipv4/udp_bpf.c`` > + > +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 can not 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 pointer to given values or to add metadata to the ``struct > +sk_msg_buff *msg``. > + > +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 Missing space between ``map`` and ( is breaking formatting. > +``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 Should be ``skb`` > +returns ``SK_PASS``), redirect it to the socket referenced by *map* (of type Should be ``map`` > +``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 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. > + > +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()`` Should be capitalized Sockmap > +helper. The ``key`` parameter is the index value of the sockmap array. And the Helpers are kernel BPF things. This is a libbpf function. > +``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()`` > +helper. Should mention that it's a socket cookie that gets returned to user space. s/helper/libbpf function/ > + > +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()`` > +helper. This helper will return 0 on success, or negative error in case of s/helper/libbpf function/ > +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 snippet shows how to create a sockmap and add a socket > +entry: > + > +.. code-block:: c > + > + /* Create a map and populate it with one socket*/ > + static void create_sample_sockmap(int s) > + { > + const 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)); > + goto out; > + } > + > + err = bpf_map_update_elem(map, &index, &s, BPF_NOEXIST); > + if (err) { > + fprintf(stderr, "Failed to update sockmap: %s\n", strerror(errno)); > + goto out; > + } > + > + out: > + close(map); > + } > + > +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/ > + > +.. _`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
