linux-kernel - Re: [PATCH v2] perf trace: Fix SIGSEGV when processing syscall args

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Date:   Fri, 8 Jul 2022 13:50:48 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>, cclaudio@...ux.ibm.com,
        Jiri Olsa <jolsa@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] perf trace: Fix SIGSEGV when processing syscall args

Hello,

On Thu, Jul 7, 2022 at 2:09 AM Naveen N. Rao
<naveen.n.rao@...ux.vnet.ibm.com> wrote:
>
> On powerpc, 'perf trace' is crashing with a SIGSEGV when trying to
> process a perf.data file created with 'perf trace record -p':
>
>   #0  0x00000001225b8988 in syscall_arg__scnprintf_augmented_string <snip> at builtin-trace.c:1492
>   #1  syscall_arg__scnprintf_filename <snip> at builtin-trace.c:1492
>   #2  syscall_arg__scnprintf_filename <snip> at builtin-trace.c:1486
>   #3  0x00000001225bdd9c in syscall_arg_fmt__scnprintf_val <snip> at builtin-trace.c:1973
>   #4  syscall__scnprintf_args <snip> at builtin-trace.c:2041
>   #5  0x00000001225bff04 in trace__sys_enter <snip> at builtin-trace.c:2319
>
> That points to the below code in tools/perf/builtin-trace.c:
>         /*
>          * If this is raw_syscalls.sys_enter, then it always comes with the 6 possible
>          * arguments, even if the syscall being handled, say "openat", uses only 4 arguments
>          * this breaks syscall__augmented_args() check for augmented args, as we calculate
>          * syscall->args_size using each syscalls:sys_enter_NAME tracefs format file,
>          * so when handling, say the openat syscall, we end up getting 6 args for the
>          * raw_syscalls:sys_enter event, when we expected just 4, we end up mistakenly
>          * thinking that the extra 2 u64 args are the augmented filename, so just check
>          * here and avoid using augmented syscalls when the evsel is the raw_syscalls one.
>          */
>         if (evsel != trace->syscalls.events.sys_enter)
>                 augmented_args = syscall__augmented_args(sc, sample, &augmented_args_size, trace->raw_augmented_syscalls_args_size);
>
> As the comment points out, we should not be trying to augment the args
> for raw_syscalls. However, when processing a perf.data file, we are not
> initializing those properly. Fix the same.
>
> Reported-by: Claudio Carvalho <cclaudio@...ux.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> ---
>  tools/perf/builtin-trace.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 897fc504918b91..f075cf37a65ef8 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -4280,6 +4280,7 @@ static int trace__replay(struct trace *trace)
>                 goto out;
>
>         evsel = evlist__find_tracepoint_by_name(session->evlist, "raw_syscalls:sys_enter");
> +       trace->syscalls.events.sys_enter = evsel;
>         /* older kernels have syscalls tp versus raw_syscalls */

Isn't it better to set it after the NULL check below?

>         if (evsel == NULL)
>                 evsel = evlist__find_tracepoint_by_name(session->evlist, "syscalls:sys_enter");
> @@ -4292,6 +4293,7 @@ static int trace__replay(struct trace *trace)
>         }
>
>         evsel = evlist__find_tracepoint_by_name(session->evlist, "raw_syscalls:sys_exit");
> +       trace->syscalls.events.sys_exit = evsel;

Ditto.

Thanks,
Namhyung


>         if (evsel == NULL)
>                 evsel = evlist__find_tracepoint_by_name(session->evlist, "syscalls:sys_exit");
>         if (evsel &&
>
> base-commit: 52f28b7bac75da9b8508f17438c9a8d83ab48e5d
> --
> 2.36.1
>