linux-kernel - Re: [PATCH -tip] bpf: Check flags for branch stack in bpf_read_branch

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Message-ID: <8af9bdd8-47d0-b9cd-57b4-0f92c8b2889a@linux.intel.com>
Date:   Tue, 27 Sep 2022 16:41:02 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>, bpf@...r.kernel.org,
        Song Liu <songliubraving@...com>, Daniel Xu <dxu@...uu.xyz>
Subject: Re: [PATCH -tip] bpf: Check flags for branch stack in
 bpf_read_branch_records helper



On 2022-09-27 4:32 p.m., Jiri Olsa wrote:
> Recent commit [1] changed branch stack data indication from
> br_stack pointer to sample_flags in perf_sample_data struct.
> 
> We need to check sample_flags for PERF_SAMPLE_BRANCH_STACK
> bit for valid branch stack data.
> 
> [1] a9a931e26668 ("perf: Use sample_flags for branch stack")
> 
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Fixes: a9a931e26668 ("perf: Use sample_flags for branch stack")
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>

Thanks for the fix.

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan

> ---
> NOTE sending on top of tip/master because [1] is not
>      merged in bpf-next/master yet
> 
>  kernel/trace/bpf_trace.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 68e5cdd24cef..1fcd1234607e 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1507,6 +1507,9 @@ BPF_CALL_4(bpf_read_branch_records, struct bpf_perf_event_data_kern *, ctx,
>  	if (unlikely(flags & ~BPF_F_GET_BRANCH_RECORDS_SIZE))
>  		return -EINVAL;
>  
> +	if (unlikely(!(ctx->data->sample_flags & PERF_SAMPLE_BRANCH_STACK)))
> +		return -ENOENT;
> +
>  	if (unlikely(!br_stack))
>  		return -ENOENT;
>