linux-kernel - [tip: perf/urgent] perf tests: Avoid raising SEGV using an obvious NULL dereference

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Date:   Mon, 07 Oct 2019 14:49:17 -0000
From:   "tip-bot2 for Ian Rogers" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Wang Nan <wangnan0@...wei.com>, Ingo Molnar <mingo@...nel.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf tests: Avoid raising SEGV using an obvious
 NULL dereference

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     e3e2cf3d5b1fe800b032e14c0fdcd9a6fb20cf3b
Gitweb:        https://git.kernel.org/tip/e3e2cf3d5b1fe800b032e14c0fdcd9a6fb20cf3b
Author:        Ian Rogers <irogers@...gle.com>
AuthorDate:    Wed, 25 Sep 2019 12:59:24 -07:00
Committer:     Arnaldo Carvalho de Melo <acme@...hat.com>
CommitterDate: Fri, 27 Sep 2019 09:26:14 -03:00

perf tests: Avoid raising SEGV using an obvious NULL dereference

An optimized build such as:

  make -C tools/perf CLANG=1 CC=clang EXTRA_CFLAGS="-O3

will turn the dereference operation into a ud2 instruction, raising a
SIGILL rather than a SIGSEGV. Use raise(..) for correctness and clarity.

Similar issues were addressed in Numfor Mbiziwo-Tiapo's patch:

  https://lkml.org/lkml/2019/7/8/1234

Committer testing:

Before:

  [root@...co ~]# perf test hooks
  55: perf hooks                                            : Ok
  [root@...co ~]# perf test -v hooks
  55: perf hooks                                            :
  --- start ---
  test child forked, pid 17092
  SIGSEGV is observed as expected, try to recover.
  Fatal error (SEGFAULT) in perf hook 'test'
  test child finished with 0
  ---- end ----
  perf hooks: Ok
  [root@...co ~]#

After:

  [root@...co ~]# perf test hooks
  55: perf hooks                                            : Ok
  [root@...co ~]# perf test -v hooks
  55: perf hooks                                            :
  --- start ---
  test child forked, pid 17909
  SIGSEGV is observed as expected, try to recover.
  Fatal error (SEGFAULT) in perf hook 'test'
  test child finished with 0
  ---- end ----
  perf hooks: Ok
  [root@...co ~]#

Fixes: a074865e60ed ("perf tools: Introduce perf hooks")
Signed-off-by: Ian Rogers <irogers@...gle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Wang Nan <wangnan0@...wei.com>
Link: http://lore.kernel.org/lkml/20190925195924.152834-2-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/tests/perf-hooks.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/perf/tests/perf-hooks.c b/tools/perf/tests/perf-hooks.c
index dbc2719..dd865e0 100644
--- a/tools/perf/tests/perf-hooks.c
+++ b/tools/perf/tests/perf-hooks.c
@@ -19,12 +19,11 @@ static void sigsegv_handler(int sig __maybe_unused)
 static void the_hook(void *_hook_flags)
 {
 	int *hook_flags = _hook_flags;
-	int *p = NULL;
 
 	*hook_flags = 1234;
 
 	/* Generate a segfault, test perf_hooks__recover */
-	*p = 0;
+	raise(SIGSEGV);
 }
 
 int test__perf_hooks(struct test *test __maybe_unused, int subtest __maybe_unused)