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

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Date:   Sun, 17 Jul 2022 11:01:01 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     cclaudio@...ux.ibm.com, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf trace: Fix SIGSEGV when processing syscall args

Em Thu, Jul 07, 2022 at 02:39:00PM +0530, Naveen N. Rao escreveu:
> 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.

Thanks, applied.

- Arnaldo

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

-- 

- Arnaldo