linux-kernel - [PATCH v2 3/4] perf machine: Avoid UB by delaying computing branch entries

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Message-Id: <20241216014637.304761-4-irogers@google.com>
Date: Sun, 15 Dec 2024 17:46:36 -0800
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>, Sun Haiyong <sunhaiyong@...ngson.cn>, 
	Yanteng Si <siyanteng@...ngson.cn>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/4] perf machine: Avoid UB by delaying computing branch entries

If the branch_stack is NULL then perf_sample__branch_entries may
return NULL+1 which triggers ubsan (undefined behavior
sanitizer). Avoid this by making the computation conditional on branch
existing.

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

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 84661d950104..7b1e1c254c17 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -2670,7 +2670,6 @@ static int thread__resolve_callchain_sample(struct thread *thread,
 					    bool symbols)
 {
 	struct branch_stack *branch = sample->branch_stack;
-	struct branch_entry *entries = perf_sample__branch_entries(sample);
 	struct ip_callchain *chain = sample->callchain;
 	int chain_nr = 0;
 	u8 cpumode = PERF_RECORD_MISC_USER;
@@ -2712,6 +2711,7 @@ static int thread__resolve_callchain_sample(struct thread *thread,
 	 */
 
 	if (branch && callchain_param.branch_callstack) {
+		struct branch_entry *entries = perf_sample__branch_entries(sample);
 		int nr = min(max_stack, (int)branch->nr);
 		struct branch_entry be[nr];
 		struct iterations iter[nr];
-- 
2.47.1.613.gc27f4b7a9f-goog