linux-kernel - Re: [PATCH] perf synthetic events: Avoid write of uninitialized memory.

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Message-ID: <YEiyFNEhMuZhXA30@krava>
Date:   Wed, 10 Mar 2021 12:48:36 +0100
From:   Jiri Olsa <jolsa@...hat.com>
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>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf synthetic events: Avoid write of uninitialized
 memory.

On Tue, Mar 09, 2021 at 03:49:45PM -0800, Ian Rogers wrote:
> Account for alignment bytes in the zero-ing memset.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/synthetic-events.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index b698046ec2db..31bf3dd6a1e0 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -424,7 +424,7 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>  
>  	while (!io.eof) {
>  		static const char anonstr[] = "//anon";
> -		size_t size;
> +		size_t size, aligned_size;
>  
>  		/* ensure null termination since stack will be reused. */
>  		event->mmap2.filename[0] = '\0';
> @@ -484,11 +484,12 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
>  		}
>  
>  		size = strlen(event->mmap2.filename) + 1;
> -		size = PERF_ALIGN(size, sizeof(u64));
> +		aligned_size = PERF_ALIGN(size, sizeof(u64));
>  		event->mmap2.len -= event->mmap.start;
>  		event->mmap2.header.size = (sizeof(event->mmap2) -
> -					(sizeof(event->mmap2.filename) - size));
> -		memset(event->mmap2.filename + size, 0, machine->id_hdr_size);
> +					(sizeof(event->mmap2.filename) - aligned_size));
> +		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
> +			(aligned_size - size));

so we did not zero the extra alignment bytes, nice ;-) looks good

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

>  		event->mmap2.header.size += machine->id_hdr_size;
>  		event->mmap2.pid = tgid;
>  		event->mmap2.tid = pid;
> -- 
> 2.30.1.766.gb4fecdf3b7-goog
>