Re: [PATCH -tip] bpf: Check flags for branch stack in bpf_read_branch_records helper

["Liang, Kan" <kan.liang@linux.intel.com>]

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@linux.intel.com>
> Fixes: a9a931e26668 ("perf: Use sample_flags for branch stack")
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Thanks for the fix.

Reviewed-by: Kan Liang <kan.liang@linux.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;
>