linux-kernel - Re: [PATCH 2/2] Avoid raising segv using an obvious null dereference

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Date:   Thu, 26 Sep 2019 12:24:19 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/2] Avoid raising segv using an obvious null dereference

Em Wed, Sep 25, 2019 at 12:59:24PM -0700, Ian Rogers escreveu:
> 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

Added:

Cc: Numfor Mbiziwo-Tiapo <nums@...gle.com>

And:

Cc: Wang Nan <wangnan0@...wei.com>
Fixes: a074865e60ed ("perf tools: Introduce perf hooks")

And:

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 ~]#


 ----------------------------------------------------------------------------

Thanks, applied.

- Arnaldo
 
> Signed-off-by: Ian Rogers <irogers@...gle.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 dbc27199c65e..dd865e0bea12 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)
> -- 
> 2.23.0.351.gc4317032e6-goog

-- 

- Arnaldo