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

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Date:   Tue, 27 Sep 2022 21:49:18 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...nel.org>
CC:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        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" <bpf@...r.kernel.org>,
        Daniel Xu <dxu@...uu.xyz>
Subject: Re: [PATCH -tip] bpf: Check flags for branch stack in
 bpf_read_branch_records helper



> On Sep 27, 2022, at 1:32 PM, Jiri Olsa <jolsa@...nel.org> 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! I noticed the issue last week, but haven't
got time to look into it. 

Song

> ---
> 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;
> 
> -- 
> 2.37.3
>