linux-kernel - Re: [PATCH v1 1/2] perf cs-etm: Always allocate memory for cs_etm_queue::prev

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Date:   Mon, 29 Apr 2019 15:53:36 +0100
From:   Robert Walker <robert.walker@....com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] perf cs-etm: Always allocate memory for
 cs_etm_queue::prev_packet

Hi,

On 28/04/2019 09:32, Leo Yan wrote:
> Robert Walker reported a segmentation fault is observed when process
> CoreSight trace data; this issue can be easily reproduced by the
> command 'perf report --itrace=i1000i' for decoding tracing data.
>
> If neither the 'b' flag (synthesize branches events) nor 'l' flag
> (synthesize last branch entries) are specified to option '--itrace',
> cs_etm_queue::prev_packet will not been initialised.  After merging
> the code to support exception packets and sample flags, there
> introduced a number of uses of cs_etm_queue::prev_packet without
> checking whether it is valid, for these cases any accessing to
> uninitialised prev_packet will cause crash.
>
> As cs_etm_queue::prev_packet is used more widely now and it's already
> hard to follow which functions have been called in a context where the
> validity of cs_etm_queue::prev_packet has been checked, this patch
> always allocates memory for cs_etm_queue::prev_packet.
>
> Reported-by: Robert Walker <robert.walker@....com>
> Suggested-by: Robert Walker <robert.walker@....com>
> Fixes: 7100b12cf474 ("perf cs-etm: Generate branch sample for exception packet")
> Fixes: 24fff5eb2b93 ("perf cs-etm: Avoid stale branch samples when flush packet")
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>   tools/perf/util/cs-etm.c | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)

I've tested these with the trace from the HiKey960 and the segfault no 
longer occurs

Tested-by: Robert Walker <robert.walker@....com>

Regards

Rob

>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 110804936fc3..054b480aab04 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -422,11 +422,9 @@ static struct cs_etm_queue *cs_etm__alloc_queue(struct cs_etm_auxtrace *etm)
>   	if (!etmq->packet)
>   		goto out_free;
>   
> -	if (etm->synth_opts.last_branch || etm->sample_branches) {
> -		etmq->prev_packet = zalloc(szp);
> -		if (!etmq->prev_packet)
> -			goto out_free;
> -	}
> +	etmq->prev_packet = zalloc(szp);
> +	if (!etmq->prev_packet)
> +		goto out_free;
>   
>   	if (etm->synth_opts.last_branch) {
>   		size_t sz = sizeof(struct branch_stack);