Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
Date:   Fri, 6 Oct 2023 14:17:55 -0700
In-Reply-To: <20231006201657.work.531-kees@kernel.org>
Mime-Version: 1.0
References: <20231006201657.work.531-kees@kernel.org>
Message-ID: <ZSB5g6CmpjS-l5nK@google.com>
Subject: Re: [PATCH] bpf: Annotate struct bpf_stack_map with __counted_by
From:   Stanislav Fomichev <sdf@google.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Song Liu <song@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Yonghong Song <yonghong.song@linux.dev>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, Hao Luo <haoluo@google.com>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>, bpf@vger.kernel.org,
        linux-hardening@vger.kernel.org,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Content-Type: text/plain; charset="utf-8"
Precedence: bulk

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@kernel.org>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Andrii Nakryiko <andrii@kernel.org>
> Cc: Martin KaFai Lau <martin.lau@linux.dev>
> Cc: Yonghong Song <yonghong.song@linux.dev>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: KP Singh <kpsingh@kernel.org>
> Cc: Stanislav Fomichev <sdf@google.com>
> Cc: Hao Luo <haoluo@google.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: bpf@vger.kernel.org
> Cc: linux-hardening@vger.kernel.org
> Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> Signed-off-by: Kees Cook <keescook@chromium.org>

TIL about __counted_by :-)

Acked-by: Stanislav Fomichev <sdf@google.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
>