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SubjectRe: [PATCH] perf core: apply calculated padding to PERF_SAMPLE_RAW output
On Tue, May 19, 2020 at 03:26:16PM +0200, Timo Beckers wrote:
> Zero the amount of padding bytes determined in perf_prepare_sample().
> This prevents garbage being read from the ring buffer after it has wrapped
> the page boundary at least once.

But it's user garbage, right? And they should be unconsumed anyway.

> Signed-off-by: Timo Beckers <timo@incline.eu>
> ---
> kernel/events/core.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 80cf996a7f19..d4e0b003ece0 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6807,8 +6807,16 @@ void perf_output_sample(struct perf_output_handle *handle,
> break;
> frag = frag->next;
> } while (1);
> - if (frag->pad)
> - __output_skip(handle, NULL, frag->pad);
> + /*
> + * The padding value is determined in
> + * perf_prepare_sample() and is not
> + * expected to exceed u64.
> + */
> + if (frag->pad) {
> + u64 zero = 0;
> +
> + __output_copy(handle, &zero, frag->pad);
> + }
> } else {
> struct {
> u32 size;
> --
> 2.26.2
>

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