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Date: Fri, 25 Sep 2020 09:26:36 +0100
From: Lorenz Bauer <lmb@...udflare.com>
To: Martin KaFai Lau <kafai@...com>
Cc: bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Kernel Team <kernel-team@...com>,
Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 bpf-next 02/13] bpf: Enable bpf_skc_to_* sock casting
helper to networking prog type
On Fri, 25 Sep 2020 at 01:04, Martin KaFai Lau <kafai@...com> wrote:
>
> There is a constant need to add more fields into the bpf_tcp_sock
> for the bpf programs running at tc, sock_ops...etc.
>
> A current workaround could be to use bpf_probe_read_kernel(). However,
> other than making another helper call for reading each field and missing
> CO-RE, it is also not as intuitive to use as directly reading
> "tp->lsndtime" for example. While already having perfmon cap to do
> bpf_probe_read_kernel(), it will be much easier if the bpf prog can
> directly read from the tcp_sock.
>
> This patch tries to do that by using the existing casting-helpers
> bpf_skc_to_*() whose func_proto returns a btf_id. For example, the
> func_proto of bpf_skc_to_tcp_sock returns the btf_id of the
> kernel "struct tcp_sock".
>
> These helpers are also added to is_ptr_cast_function().
> It ensures the returning reg (BPF_REF_0) will also carries the ref_obj_id.
> That will keep the ref-tracking works properly.
>
> The bpf_skc_to_* helpers are made available to most of the bpf prog
> types in filter.c. The bpf_skc_to_* helpers will be limited by
> perfmon cap.
>
> This patch adds a ARG_PTR_TO_BTF_ID_SOCK_COMMON. The helper accepting
> this arg can accept a btf-id-ptr (PTR_TO_BTF_ID + &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON])
> or a legacy-ctx-convert-skc-ptr (PTR_TO_SOCK_COMMON). The bpf_skc_to_*()
> helpers are changed to take ARG_PTR_TO_BTF_ID_SOCK_COMMON such that
> they will accept pointer obtained from skb->sk.
>
> Instead of specifying both arg_type and arg_btf_id in the same func_proto
> which is how the current ARG_PTR_TO_BTF_ID does, the arg_btf_id of
> the new ARG_PTR_TO_BTF_ID_SOCK_COMMON is specified in the
> compatible_reg_types[] in verifier.c. The reason is the arg_btf_id is
> always the same. Discussion in this thread:
> https://lore.kernel.org/bpf/20200922070422.1917351-1-kafai@fb.com/
>
> The ARG_PTR_TO_BTF_ID_ part gives a clear expectation that the helper is
> expecting a PTR_TO_BTF_ID which could be NULL. This is the same
> behavior as the existing helper taking ARG_PTR_TO_BTF_ID.
>
> The _SOCK_COMMON part means the helper is also expecting the legacy
> SOCK_COMMON pointer.
>
> By excluding the _OR_NULL part, the bpf prog cannot call helper
> with a literal NULL which doesn't make sense in most cases.
> e.g. bpf_skc_to_tcp_sock(NULL) will be rejected. All PTR_TO_*_OR_NULL
> reg has to do a NULL check first before passing into the helper or else
> the bpf prog will be rejected. This behavior is nothing new and
> consistent with the current expectation during bpf-prog-load.
>
> [ ARG_PTR_TO_BTF_ID_SOCK_COMMON will be used to replace
> ARG_PTR_TO_SOCK* of other existing helpers later such that
> those existing helpers can take the PTR_TO_BTF_ID returned by
> the bpf_skc_to_*() helpers.
>
> The only special case is bpf_sk_lookup_assign() which can accept a
> literal NULL ptr. It has to be handled specially in another follow
> up patch if there is a need (e.g. by renaming ARG_PTR_TO_SOCKET_OR_NULL
> to ARG_PTR_TO_BTF_ID_SOCK_COMMON_OR_NULL). ]
>
> [ When converting the older helpers that take ARG_PTR_TO_SOCK* in
> the later patch, if the kernel does not support BTF,
> ARG_PTR_TO_BTF_ID_SOCK_COMMON will behave like ARG_PTR_TO_SOCK_COMMON
> because no reg->type could have PTR_TO_BTF_ID in this case.
>
> It is not a concern for the newer-btf-only helper like the bpf_skc_to_*()
> here though because these helpers must require BTF vmlinux to begin
> with. ]
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
> include/linux/bpf.h | 1 +
> kernel/bpf/verifier.c | 34 +++++++++++++++++++--
> net/core/filter.c | 69 ++++++++++++++++++++++++++++++-------------
> 3 files changed, 82 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index fc5c901c7542..d0937f1d2980 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -292,6 +292,7 @@ enum bpf_arg_type {
> ARG_PTR_TO_ALLOC_MEM, /* pointer to dynamically allocated memory */
> ARG_PTR_TO_ALLOC_MEM_OR_NULL, /* pointer to dynamically allocated memory or NULL */
> ARG_CONST_ALLOC_SIZE_OR_ZERO, /* number of allocated bytes requested */
> + ARG_PTR_TO_BTF_ID_SOCK_COMMON, /* pointer to in-kernel sock_common or bpf-mirrored bpf_sock */
> __BPF_ARG_TYPE_MAX,
> };
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 945fa2b4d096..d4ba29fb17a6 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -486,7 +486,12 @@ static bool is_acquire_function(enum bpf_func_id func_id,
> static bool is_ptr_cast_function(enum bpf_func_id func_id)
> {
> return func_id == BPF_FUNC_tcp_sock ||
> - func_id == BPF_FUNC_sk_fullsock;
> + func_id == BPF_FUNC_sk_fullsock ||
> + func_id == BPF_FUNC_skc_to_tcp_sock ||
> + func_id == BPF_FUNC_skc_to_tcp6_sock ||
> + func_id == BPF_FUNC_skc_to_udp6_sock ||
> + func_id == BPF_FUNC_skc_to_tcp_timewait_sock ||
> + func_id == BPF_FUNC_skc_to_tcp_request_sock;
> }
>
> /* string representation of 'enum bpf_reg_type' */
> @@ -3953,6 +3958,7 @@ static int resolve_map_arg_type(struct bpf_verifier_env *env,
>
> struct bpf_reg_types {
> const enum bpf_reg_type types[10];
> + u32 *btf_id;
> };
>
> static const struct bpf_reg_types map_key_value_types = {
> @@ -3973,6 +3979,17 @@ static const struct bpf_reg_types sock_types = {
> },
> };
>
> +static const struct bpf_reg_types btf_id_sock_common_types = {
> + .types = {
> + PTR_TO_SOCK_COMMON,
> + PTR_TO_SOCKET,
> + PTR_TO_TCP_SOCK,
> + PTR_TO_XDP_SOCK,
> + PTR_TO_BTF_ID,
> + },
> + .btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
> +};
> +
> static const struct bpf_reg_types mem_types = {
> .types = {
> PTR_TO_STACK,
> @@ -4014,6 +4031,7 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
> [ARG_PTR_TO_CTX] = &context_types,
> [ARG_PTR_TO_CTX_OR_NULL] = &context_types,
> [ARG_PTR_TO_SOCK_COMMON] = &sock_types,
> + [ARG_PTR_TO_BTF_ID_SOCK_COMMON] = &btf_id_sock_common_types,
> [ARG_PTR_TO_SOCKET] = &fullsock_types,
> [ARG_PTR_TO_SOCKET_OR_NULL] = &fullsock_types,
> [ARG_PTR_TO_BTF_ID] = &btf_ptr_types,
> @@ -4059,6 +4077,14 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
>
> found:
> if (type == PTR_TO_BTF_ID) {
> + if (!arg_btf_id) {
> + if (!compatible->btf_id) {
> + verbose(env, "verifier internal error: missing arg compatible BTF ID\n");
> + return -EFAULT;
> + }
> + arg_btf_id = compatible->btf_id;
> + }
> +
> if (!btf_struct_ids_match(&env->log, reg->off, reg->btf_id,
> *arg_btf_id)) {
> verbose(env, "R%d is of type %s but %s is expected\n",
> @@ -4575,10 +4601,14 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
> {
> int i;
>
> - for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++)
> + for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
> if (fn->arg_type[i] == ARG_PTR_TO_BTF_ID && !fn->arg_btf_id[i])
> return false;
>
> + if (fn->arg_type[i] != ARG_PTR_TO_BTF_ID && fn->arg_btf_id[i])
> + return false;
> + }
> +
This is a hold over from the previous patchset?
> return true;
> }
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 706f8db0ccf8..6d1864f2bd51 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -77,6 +77,9 @@
> #include <net/transp_v6.h>
> #include <linux/btf_ids.h>
>
> +static const struct bpf_func_proto *
> +bpf_sk_base_func_proto(enum bpf_func_id func_id);
> +
> int copy_bpf_fprog_from_user(struct sock_fprog *dst, sockptr_t src, int len)
> {
> if (in_compat_syscall()) {
> @@ -6620,7 +6623,7 @@ sock_addr_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return NULL;
> }
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6639,7 +6642,7 @@ sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> case BPF_FUNC_perf_event_output:
> return &bpf_skb_event_output_proto;
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6800,7 +6803,7 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_sk_assign_proto;
> #endif
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6841,7 +6844,7 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_tcp_gen_syncookie_proto;
> #endif
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6883,7 +6886,7 @@ sock_ops_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_tcp_sock_proto;
> #endif /* CONFIG_INET */
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6929,7 +6932,7 @@ sk_msg_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_get_cgroup_classid_curr_proto;
> #endif
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6971,7 +6974,7 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_skc_lookup_tcp_proto;
> #endif
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -6982,7 +6985,7 @@ flow_dissector_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> case BPF_FUNC_skb_load_bytes:
> return &bpf_flow_dissector_load_bytes_proto;
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -7009,7 +7012,7 @@ lwt_out_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> case BPF_FUNC_skb_under_cgroup:
> return &bpf_skb_under_cgroup_proto;
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -9746,7 +9749,7 @@ sk_lookup_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> case BPF_FUNC_sk_release:
> return &bpf_sk_release_proto;
> default:
> - return bpf_base_func_proto(func_id);
> + return bpf_sk_base_func_proto(func_id);
> }
> }
>
> @@ -9913,8 +9916,7 @@ const struct bpf_func_proto bpf_skc_to_tcp6_sock_proto = {
> .func = bpf_skc_to_tcp6_sock,
> .gpl_only = false,
> .ret_type = RET_PTR_TO_BTF_ID_OR_NULL,
> - .arg1_type = ARG_PTR_TO_BTF_ID,
> - .arg1_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
> + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> .ret_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_TCP6],
> };
>
> @@ -9930,8 +9932,7 @@ const struct bpf_func_proto bpf_skc_to_tcp_sock_proto = {
> .func = bpf_skc_to_tcp_sock,
> .gpl_only = false,
> .ret_type = RET_PTR_TO_BTF_ID_OR_NULL,
> - .arg1_type = ARG_PTR_TO_BTF_ID,
> - .arg1_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
> + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> .ret_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_TCP],
> };
>
> @@ -9954,8 +9955,7 @@ const struct bpf_func_proto bpf_skc_to_tcp_timewait_sock_proto = {
> .func = bpf_skc_to_tcp_timewait_sock,
> .gpl_only = false,
> .ret_type = RET_PTR_TO_BTF_ID_OR_NULL,
> - .arg1_type = ARG_PTR_TO_BTF_ID,
> - .arg1_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
> + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> .ret_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_TCP_TW],
> };
>
> @@ -9978,8 +9978,7 @@ const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto = {
> .func = bpf_skc_to_tcp_request_sock,
> .gpl_only = false,
> .ret_type = RET_PTR_TO_BTF_ID_OR_NULL,
> - .arg1_type = ARG_PTR_TO_BTF_ID,
> - .arg1_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
> + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> .ret_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_TCP_REQ],
> };
>
> @@ -10000,7 +9999,37 @@ const struct bpf_func_proto bpf_skc_to_udp6_sock_proto = {
> .func = bpf_skc_to_udp6_sock,
> .gpl_only = false,
> .ret_type = RET_PTR_TO_BTF_ID_OR_NULL,
> - .arg1_type = ARG_PTR_TO_BTF_ID,
> - .arg1_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
> + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> .ret_btf_id = &btf_sock_ids[BTF_SOCK_TYPE_UDP6],
> };
> +
> +static const struct bpf_func_proto *
> +bpf_sk_base_func_proto(enum bpf_func_id func_id)
> +{
> + const struct bpf_func_proto *func;
> +
> + switch (func_id) {
> + case BPF_FUNC_skc_to_tcp6_sock:
> + func = &bpf_skc_to_tcp6_sock_proto;
> + break;
> + case BPF_FUNC_skc_to_tcp_sock:
> + func = &bpf_skc_to_tcp_sock_proto;
> + break;
> + case BPF_FUNC_skc_to_tcp_timewait_sock:
> + func = &bpf_skc_to_tcp_timewait_sock_proto;
> + break;
> + case BPF_FUNC_skc_to_tcp_request_sock:
> + func = &bpf_skc_to_tcp_request_sock_proto;
> + break;
> + case BPF_FUNC_skc_to_udp6_sock:
> + func = &bpf_skc_to_udp6_sock_proto;
> + break;
> + default:
> + return bpf_base_func_proto(func_id);
> + }
> +
> + if (!perfmon_capable())
> + return NULL;
> +
> + return func;
> +}
> --
> 2.24.1
>
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
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