linux-kernel - [PATCH v1] libperf mmap: In user mmap rdpmc avoid undefined behavior

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Message-ID: <20250914182437.1959331-1-irogers@google.com>
Date: Sun, 14 Sep 2025 11:24:37 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] libperf mmap: In user mmap rdpmc avoid undefined behavior

A shift left of a signed 64-bit s64 may overflow and result in
undefined behavior caught by ubsan. Switch to a u64 instead.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/lib/perf/mmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
index c1a51d925e0e..ec124eb0ec0a 100644
--- a/tools/lib/perf/mmap.c
+++ b/tools/lib/perf/mmap.c
@@ -508,7 +508,7 @@ int perf_mmap__read_self(struct perf_mmap *map, struct perf_counts_values *count
 		idx = READ_ONCE(pc->index);
 		cnt = READ_ONCE(pc->offset);
 		if (pc->cap_user_rdpmc && idx) {
-			s64 evcnt = read_perf_counter(idx - 1);
+			u64 evcnt = read_perf_counter(idx - 1);
 			u16 width = READ_ONCE(pc->pmc_width);
 
 			evcnt <<= 64 - width;
-- 
2.51.0.384.g4c02a37b29-goog