netdev - Re: [PATCH v3 bpf-next 04/11] bpf: add attach_btf

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Date:   Wed, 16 Oct 2019 12:45:32 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>, x86@...nel.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 04/11] bpf: add attach_btf_id attribute to
 program load

On Wed, Oct 16, 2019 at 4:15 AM Alexei Starovoitov <ast@...nel.org> wrote:
>
> Add attach_btf_id attribute to prog_load command.
> It's similar to existing expected_attach_type attribute which is
> used in several cgroup based program types.
> Unfortunately expected_attach_type is ignored for
> tracing programs and cannot be reused for new purpose.
> Hence introduce attach_btf_id to verify bpf programs against
> given in-kernel BTF type id at load time.
> It is strictly checked to be valid for raw_tp programs only.
> In a later patches it will become:
> btf_id == 0 semantics of existing raw_tp progs.
> btd_id > 0 raw_tp with BTF and additional type safety.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> Acked-by: Andrii Nakryiko <andriin@...com>
> ---
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       |  1 +
>  kernel/bpf/syscall.c           | 18 ++++++++++++++----
>  tools/include/uapi/linux/bpf.h |  1 +
>  4 files changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 282e28bf41ec..f916380675dd 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -375,6 +375,7 @@ struct bpf_prog_aux {
>         u32 id;
>         u32 func_cnt; /* used by non-func prog as the number of func progs */
>         u32 func_idx; /* 0 for non-func prog, the index in func array for func prog */
> +       u32 attach_btf_id; /* in-kernel BTF type id to attach to */
>         bool verifier_zext; /* Zero extensions has been inserted by verifier. */
>         bool offload_requested;
>         struct bpf_prog **func;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a65c3b0c6935..3bb2cd1de341 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -420,6 +420,7 @@ union bpf_attr {
>                 __u32           line_info_rec_size;     /* userspace bpf_line_info size */
>                 __aligned_u64   line_info;      /* line info */
>                 __u32           line_info_cnt;  /* number of bpf_line_info records */
> +               __u32           attach_btf_id;  /* in-kernel BTF type id to attach to */
>         };
>
>         struct { /* anonymous struct used by BPF_OBJ_* commands */
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 82eabd4e38ad..b56c482c9760 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -23,6 +23,7 @@
>  #include <linux/timekeeping.h>
>  #include <linux/ctype.h>
>  #include <linux/nospec.h>
> +#include <uapi/linux/btf.h>
>
>  #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PROG_ARRAY || \
>                            (map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
> @@ -1565,8 +1566,9 @@ static void bpf_prog_load_fixup_attach_type(union bpf_attr *attr)
>  }
>
>  static int
> -bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
> -                               enum bpf_attach_type expected_attach_type)
> +bpf_prog_load_check_attach(enum bpf_prog_type prog_type,
> +                          enum bpf_attach_type expected_attach_type,
> +                          u32 btf_id)
>  {
>         switch (prog_type) {
>         case BPF_PROG_TYPE_CGROUP_SOCK:
> @@ -1608,13 +1610,19 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
>                 default:
>                         return -EINVAL;
>                 }
> +       case BPF_PROG_TYPE_RAW_TRACEPOINT:
> +               if (btf_id > BTF_MAX_TYPE)
> +                       return -EINVAL;
> +               return 0;
>         default:
> +               if (btf_id)
> +                       return -EINVAL;

this is minor issue, feel free to fix in a follow up patch, but this
check should be done for all cases but BPF_PROG_TYPE_RAW_TRACEPOINT,
not just for default (default will ignore a bunch of cgroup attach
types).

>                 return 0;
>         }
>  }
>