linux-kernel - [PATCH] perf core: apply calculated padding to PERF_SAMPLE

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Message-Id: <20200519132616.794171-1-timo@incline.eu>
Date:   Tue, 19 May 2020 15:26:16 +0200
From:   Timo Beckers <timo@...line.eu>
To:     unlisted-recipients:; (no To-header on input)
Cc:     timo@...line.eu, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org (open list:PERFORMANCE EVENTS SUBSYSTEM)
Subject: [PATCH] perf core: apply calculated padding to PERF_SAMPLE_RAW output

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.

Signed-off-by: Timo Beckers <timo@...line.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