linux-kernel - Re: [PATCH v2 4/7] perf intel-tpebs: Avoid race when evlist is being deleted

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

Message-ID: <aDdNk1IOqtyM44AX@google.com>
Date: Wed, 28 May 2025 10:53:23 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: 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@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
	James Clark <james.clark@...aro.org>,
	Howard Chu <howardchu95@...il.com>,
	Weilin Wang <weilin.wang@...el.com>,
	Stephen Brennan <stephen.s.brennan@...cle.com>,
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] perf intel-tpebs: Avoid race when evlist is being
 deleted

Hi Ian,

On Tue, May 27, 2025 at 08:26:34PM -0700, Ian Rogers wrote:
> Reading through the evsel->evlist may seg fault if a sample arrives
> when the evlist is being deleted. Detect this case and ignore samples
> arriving when the evlist is being deleted.
> 
> Fixes: bcfab08db7fb ("perf intel-tpebs: Filter non-workload samples")
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/intel-tpebs.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/intel-tpebs.c b/tools/perf/util/intel-tpebs.c
> index 4ad4bc118ea5..3b92ebf5c112 100644
> --- a/tools/perf/util/intel-tpebs.c
> +++ b/tools/perf/util/intel-tpebs.c
> @@ -162,9 +162,17 @@ static bool is_child_pid(pid_t parent, pid_t child)
>  
>  static bool should_ignore_sample(const struct perf_sample *sample, const struct tpebs_retire_lat *t)
>  {
> -	pid_t workload_pid = t->evsel->evlist->workload.pid;
> -	pid_t sample_pid = sample->pid;
> +	pid_t workload_pid, sample_pid = sample->pid;
>  
> +	/*
> +	 * During evlist__purge the evlist will be removed prior to the
> +	 * evsel__exit calling evsel__tpebs_close and taking the
> +	 * tpebs_mtx. Avoid a segfault by ignoring samples in this case.
> +	 */
> +	if (t->evsel->evlist == NULL)
> +		return true;
> +
> +	workload_pid = t->evsel->evlist->workload.pid;

I'm curious if there's a chance of TOCTOU race.  It'd certainly help
the segfault but would this code prevent it completely?

Thanks,
Namhyung


>  	if (workload_pid < 0 || workload_pid == sample_pid)
>  		return false;
>  
> -- 
> 2.49.0.1238.gf8c92423fb-goog
>