linux-kernel - Re: [PATCH] perf tools: Fix perf_evlist__mmap

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Date:	Mon, 07 Oct 2013 09:48:31 -0600
From:	David Ahern <dsahern@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] perf tools: Fix perf_evlist__mmap_read event overflow

On 10/2/13 7:46 AM, Jiri Olsa wrote:
> The perf_evlist__mmap_read used 'union perf_event'
> as a placeholder for event crossing the mmap boundary.
>
> This is ok for sample shorter than ~PATH_MAX. However
> we could grow up to the maximum sample size which is
> 16 bits max.
>
> I hit this overflow issue when using 'perf top -G dwarf'
> which produces sample with the size around 8192 bytes.
> We could configure any valid sample size here using:
> '-G dwarf,size'.
>
> Using array with sample max size instead for the event
> placeholder. Also adding another safe check for the
> dynamic size of the user stack.
>
> TODO: The 'struct perf_mmap' is quite big now, maybe we
> could use some lazy allocation for event_copy size.

I was going to suggest just that -- dynamically handle the use of 
event_copy. The below adds ~60k per mmap. Otherwise...

Acked-by: David Ahern <dsahern@...il.com>


>
> Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> ---
>   tools/perf/util/event.h  | 3 +++
>   tools/perf/util/evlist.c | 4 ++--
>   tools/perf/util/evlist.h | 2 +-
>   tools/perf/util/evsel.c  | 3 +++
>   4 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
> index 9f50f88..2b8032a 100644
> --- a/tools/perf/util/event.h
> +++ b/tools/perf/util/event.h
> @@ -75,6 +75,9 @@ struct throttle_event {
>   	 PERF_SAMPLE_CPU | PERF_SAMPLE_PERIOD |		\
>   	 PERF_SAMPLE_IDENTIFIER)
>
> +/* perf sample has 16 bits size limit */
> +#define PERF_SAMPLE_MAX_SIZE (1 << 16)
> +
>   struct sample_event {
>   	struct perf_event_header        header;
>   	u64 array[];
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index f0d71a9..cb9523f 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -540,7 +540,7 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
>   		if ((old & md->mask) + size != ((old + size) & md->mask)) {
>   			unsigned int offset = old;
>   			unsigned int len = min(sizeof(*event), size), cpy;
> -			void *dst = &md->event_copy;
> +			void *dst = md->event_copy;
>
>   			do {
>   				cpy = min(md->mask + 1 - (offset & md->mask), len);
> @@ -550,7 +550,7 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
>   				len -= cpy;
>   			} while (len);
>
> -			event = &md->event_copy;
> +			event = (union perf_event *) md->event_copy;
>   		}
>
>   		old += size;
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 871b55a..722618f 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -21,7 +21,7 @@ struct perf_mmap {
>   	void		 *base;
>   	int		 mask;
>   	unsigned int	 prev;
> -	union perf_event event_copy;
> +	char		 event_copy[PERF_SAMPLE_MAX_SIZE];
>   };
>
>   struct perf_evlist {
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 0ce9feb..aa20ee2 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1453,6 +1453,9 @@ int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
>   			array = (void *)array + sz;
>   			OVERFLOW_CHECK_u64(array);
>   			data->user_stack.size = *array++;
> +			if (WARN_ONCE(data->user_stack.size > sz,
> +				      "user stack dump failure\n"))
> +				return -EFAULT;
>   		}
>   	}
>
>

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