linux-kernel - [PATCH] perf record: skip synthesize event when open evsel failed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20251023015043.38868-1-xueshuai@linux.alibaba.com>
Date: Thu, 23 Oct 2025 09:50:43 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
To: alexander.shishkin@...ux.intel.com,
	peterz@...radead.org,
	james.clark@....com,
	leo.yan@...aro.org,
	irogers@...gle.com
Cc: mingo@...hat.com,
	baolin.wang@...ux.alibaba.com,
	acme@...nel.org,
	mark.rutland@....com,
	jolsa@...nel.org,
	namhyung@...nel.org,
	adrian.hunter@...el.com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	nathan@...nel.org,
	bpf@...r.kernel.org
Subject: [PATCH] perf record: skip synthesize event when open evsel failed

When using perf record with the `--overwrite` option, a segmentation fault
occurs if an event fails to open. For example:

  perf record -e cycles-ct -F 1000 -a --overwrite
  Error:
  cycles-ct:H: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
  perf: Segmentation fault
      #0 0x6466b6 in dump_stack debug.c:366
      #1 0x646729 in sighandler_dump_stack debug.c:378
      #2 0x453fd1 in sigsegv_handler builtin-record.c:722
      #3 0x7f8454e65090 in __restore_rt libc-2.32.so[54090]
      #4 0x6c5671 in __perf_event__synthesize_id_index synthetic-events.c:1862
      #5 0x6c5ac0 in perf_event__synthesize_id_index synthetic-events.c:1943
      #6 0x458090 in record__synthesize builtin-record.c:2075
      #7 0x45a85a in __cmd_record builtin-record.c:2888
      #8 0x45deb6 in cmd_record builtin-record.c:4374
      #9 0x4e5e33 in run_builtin perf.c:349
      #10 0x4e60bf in handle_internal_command perf.c:401
      #11 0x4e6215 in run_argv perf.c:448
      #12 0x4e653a in main perf.c:555
      #13 0x7f8454e4fa72 in __libc_start_main libc-2.32.so[3ea72]
      #14 0x43a3ee in _start ??:0

The --overwrite option implies --tail-synthesize, which collects non-sample
events reflecting the system status when recording finishes. However, when
evsel opening fails (e.g., unsupported event 'cycles-ct'), session->evlist
is not initialized and remains NULL. The code unconditionally calls
record__synthesize() in the error path, which iterates through the NULL
evlist pointer and causes a segfault.

To fix it, move the record__synthesize() call inside the error check block, so
it's only called when there was no error during recording, ensuring that evlist
is properly initialized.

Fixes: 4ea648aec019 ("perf record: Add --tail-synthesize option")
Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
---
 tools/perf/builtin-record.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index d76f01956e33..b1fb87016d5a 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -2883,11 +2883,11 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 		rec->bytes_written += off_cpu_write(rec->session);
 
 	record__read_lost_samples(rec);
-	record__synthesize(rec, true);
 	/* this will be recalculated during process_buildids() */
 	rec->samples = 0;
 
 	if (!err) {
+		record__synthesize(rec, true);
 		if (!rec->timestamp_filename) {
 			record__finish_output(rec);
 		} else {
-- 
2.39.3