linux-kernel - Re: [PATCH] bpf: Annotate struct bpf_stack_map with __counted

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Message-ID: <ZSB5g6CmpjS-l5nK@google.com>
Date:   Fri, 6 Oct 2023 14:17:55 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Song Liu <song@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>, bpf@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] bpf: Annotate struct bpf_stack_map with __counted_by

On 10/06, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct bpf_stack_map.
> 
> Cc: Song Liu <song@...nel.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Andrii Nakryiko <andrii@...nel.org>
> Cc: Martin KaFai Lau <martin.lau@...ux.dev>
> Cc: Yonghong Song <yonghong.song@...ux.dev>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: KP Singh <kpsingh@...nel.org>
> Cc: Stanislav Fomichev <sdf@...gle.com>
> Cc: Hao Luo <haoluo@...gle.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: bpf@...r.kernel.org
> Cc: linux-hardening@...r.kernel.org
> Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> Signed-off-by: Kees Cook <keescook@...omium.org>

TIL about __counted_by :-)

Acked-by: Stanislav Fomichev <sdf@...gle.com>

> ---
>  kernel/bpf/stackmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index 458bb80b14d5..d6b277482085 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -28,7 +28,7 @@ struct bpf_stack_map {
>  	void *elems;
>  	struct pcpu_freelist freelist;
>  	u32 n_buckets;
> -	struct stack_map_bucket *buckets[];
> +	struct stack_map_bucket *buckets[] __counted_by(n_buckets);
>  };
>  
>  static inline bool stack_map_use_build_id(struct bpf_map *map)
> -- 
> 2.34.1
>