linux-kernel - Re: [PATCH] perf/x86/uncore: remove event

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Date:   Wed, 16 Nov 2016 09:45:23 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     kan.liang@...el.com
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        davej@...emonkey.org.uk, dvyukov@...gle.com, eranian@...il.com,
        linux-kernel@...r.kernel.org,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Stephane Eranian <eranian@...gle.com>,
        Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] perf/x86/uncore: remove event_list for snb client uncore
 IMC


* kan.liang@...el.com <kan.liang@...el.com> wrote:

> From: Kan Liang <kan.liang@...el.com>
> 
> A BUG was found by perf_fuzzer after enabled KASAN.
> [  205.748005] BUG: KASAN: slab-out-of-bounds in
> snb_uncore_imc_event_del+0x6c/0xa0 at addr ffff8800caa43768

> Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
> Tested-by: Vince Weaver <vincent.weaver@...ne.edu>
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  arch/x86/events/intel/uncore_snb.c | 12 ------------
>  1 file changed, 12 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore_snb.c b/arch/x86/events/intel/uncore_snb.c
> index 81195cc..a3dcc12 100644
> --- a/arch/x86/events/intel/uncore_snb.c
> +++ b/arch/x86/events/intel/uncore_snb.c
> @@ -490,24 +490,12 @@ static int snb_uncore_imc_event_add(struct perf_event *event, int flags)
>  
>  	snb_uncore_imc_event_start(event, 0);
>  
> -	box->n_events++;
> -
>  	return 0;
>  }
>  
>  static void snb_uncore_imc_event_del(struct perf_event *event, int flags)
>  {
> -	struct intel_uncore_box *box = uncore_event_to_box(event);
> -	int i;
> -
>  	snb_uncore_imc_event_stop(event, PERF_EF_UPDATE);
> -
> -	for (i = 0; i < box->n_events; i++) {
> -		if (event == box->event_list[i]) {
> -			--box->n_events;
> -			break;
> -		}
> -	}

I'll apply this fix - but could we please also make sure box->event_list[] 
_always_ get initialized to a sane state?

If it had a proper zero initial value in box->n_events the bug would not have 
triggered. So struct intel_uncore_box initialization appears to be sloppy,
and that should be looked at as well...

Thanks,

	Ingo