Messages in this thread | | | From | Namhyung Kim <> | Date | Sat, 24 Sep 2022 09:52:09 -0700 | Subject | Re: [PATCH] perf record: Fix segmentation fault in record__read_lost_samples() |
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Hi Leo,
On Sat, Sep 24, 2022 at 4:34 AM Leo Yan <leo.yan@linaro.org> wrote: > > Commit a49aa8a54e86 ("perf record: Read and inject LOST_SAMPLES events") > causes segmentation fault when run the "perf mem record" command in > unprivileged mode, the output log is: > > $ ./perf mem record --all-user -o perf_test.data -- ./test_program > Error: > Access to performance monitoring and observability operations is limited. > Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open > access to performance monitoring and observability operations for processes > without CAP_PERFMON, CAP_SYS_PTRACE or CAP_SYS_ADMIN Linux capability. > More information can be found at 'Perf events and tool security' document: > https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html > perf_event_paranoid setting is 4: > -1: Allow use of (almost) all events by all users > Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK > >= 0: Disallow raw and ftrace function tracepoint access > >= 1: Disallow CPU event access > >= 2: Disallow kernel profiling > To make the adjusted perf_event_paranoid setting permanent preserve it > in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>) > perf: Segmentation fault > Obtained 16 stack frames. > ./perf(dump_stack+0x31) [0x55b7aa1e8070] > ./perf(sighandler_dump_stack+0x36) [0x55b7aa1e815e] > ./perf(+0xc9120) [0x55b7aa0a9120] > /lib/x86_64-linux-gnu/libc.so.6(+0x4251f) [0x7fd03ef8151f] > ./perf(+0xccaca) [0x55b7aa0acaca] > ./perf(+0xcf4ab) [0x55b7aa0af4ab] > ./perf(cmd_record+0xd50) [0x55b7aa0b28df] > ./perf(+0x112f77) [0x55b7aa0f2f77] > ./perf(cmd_mem+0x53b) [0x55b7aa0f406c] > ./perf(+0x19979c) [0x55b7aa17979c] > ./perf(+0x199a37) [0x55b7aa179a37] > ./perf(+0x199b95) [0x55b7aa179b95] > ./perf(main+0x2c7) [0x55b7aa179fbd] > /lib/x86_64-linux-gnu/libc.so.6(+0x29d8f) [0x7fd03ef68d8f] > /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x7f) [0x7fd03ef68e3f] > ./perf(_start+0x24) [0x55b7aa089974] > Segmentation fault (core dumped) > > In the unprivileged mode perf fails to open PMU event, the function > record__open() returns error and "session->evlist" is NULL; this leads > to segmentation fault when iterates "session->evlist" in the function > record__read_lost_samples(). > > This patch checks "session->evlist" in record__read_lost_samples(), if > "session->evlist" is NULL then the function directly bails out to avoid > segmentation fault. > > Fixes: a49aa8a54e86 ("perf record: Read and inject LOST_SAMPLES events") > Signed-off-by: Leo Yan <leo.yan@linaro.org>
Thanks for the fix and sorry for the inconvenience. Actually I sent the same fix a few weeks ago.
https://lore.kernel.org/r/20220909235024.278281-1-namhyung@kernel.org
Thanks, Namhyung
> --- > tools/perf/builtin-record.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index 02e38f50a138..012b46dd4999 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -1888,6 +1888,10 @@ static void record__read_lost_samples(struct record *rec) > struct perf_record_lost_samples *lost; > struct evsel *evsel; > > + /* No any event is opened, directly bail out */ > + if (!session->evlist) > + return; > + > lost = zalloc(PERF_SAMPLE_MAX_SIZE); > if (lost == NULL) { > pr_debug("Memory allocation failed\n"); > -- > 2.34.1 >
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