linux-kernel - Re: [PATCH bpf-next v2 2/2] bpf: Refactor bpf_tracing_func_proto() and remove bpf_get_probe_write

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Message-ID: <CANpmjNOpY0zjpVJe8zUYZR2oJ--=OtWdHnEp70SxmAnb5ubwbQ@mail.gmail.com>
Date: Wed, 27 Nov 2024 13:06:52 +0100
From: Marco Elver <elver@...gle.com>
To: elver@...gle.com, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Nikola Grcevski <nikola.grcevski@...fana.com>, bpf@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/2] bpf: Refactor bpf_tracing_func_proto()
 and remove bpf_get_probe_write_proto()

On Wed, 27 Nov 2024 at 12:10, Marco Elver <elver@...gle.com> wrote:
>
> With bpf_get_probe_write_proto() no longer printing a message, we can
> avoid it being a special case with its own permission check.
>
> Refactor bpf_tracing_func_proto() similar to bpf_base_func_proto() to
> have a section conditional on bpf_token_capable(CAP_SYS_ADMIN), where
> the proto for bpf_probe_write_user() is returned. Finally, remove the
> unnecessary bpf_get_probe_write_proto().
>
> This simplifies the code, and adding additional CAP_SYS_ADMIN-only
> helpers in future avoids duplicating the same CAP_SYS_ADMIN check.
>
> Suggested-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
> v2:
> * New patch.
> ---
>  kernel/trace/bpf_trace.c | 30 ++++++++++++++++++------------
>  1 file changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0ab56af2e298..d312b77993dc 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -357,14 +357,6 @@ static const struct bpf_func_proto bpf_probe_write_user_proto = {
>         .arg3_type      = ARG_CONST_SIZE,
>  };
>
> -static const struct bpf_func_proto *bpf_get_probe_write_proto(void)
> -{
> -       if (!capable(CAP_SYS_ADMIN))
> -               return NULL;
> -
> -       return &bpf_probe_write_user_proto;
> -}
> -
>  #define MAX_TRACE_PRINTK_VARARGS       3
>  #define BPF_TRACE_PRINTK_SIZE          1024
>
> @@ -1417,6 +1409,12 @@ late_initcall(bpf_key_sig_kfuncs_init);
>  static const struct bpf_func_proto *
>  bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  {
> +       const struct bpf_func_proto *func_proto;
> +
> +       func_proto = bpf_base_func_proto(func_id, prog);
> +       if (func_proto)
> +               return func_proto;

As indicated by the patch robot failure, we can't move this call up
and needs to remain the last call after all others because we may
override a function proto in bpf_base_func_proto here (like done for
BPF_FUNC_get_smp_processor_id).

Let me fix that.