linux-kernel - Re: perf: fuzzer KASAN unwind_get_return

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Date:   Thu, 17 Nov 2016 09:18:48 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "davej@...emonkey.org.uk" <davej@...emonkey.org.uk>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        Stephane Eranian <eranian@...il.com>
Subject: Re: perf: fuzzer KASAN unwind_get_return_address

On Thu, Nov 17, 2016 at 10:04:46AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 16, 2016 at 10:48:28PM -0600, Josh Poimboeuf wrote:
> > Peter or Vince, can you try to recreate with this patch?  It dumps the
> > raw stack contents during a stack dump.  Hopefully that would give a
> > clue about what's going wrong.
> 
> 
> Here goes... I'll do another run and get you the results of that as
> well.

Thanks, I just waded through this and it turned up some good clues.  And
according to 'git blame', you might be able to help :-)

It's not stack corruption.  Instead it looks like
__intel_pmu_pebs_event() is creating a bad or stale pt_regs which gets
passed to the unwinder.  Specifically, regs->bp points to a seemingly
random address on the NMI stack.  Which seems odd, considering the code
itself is running on the same NMI stack.

I don't know much about the PEBS code but it seems like it's passing
some stale data.  Either that or there's some NMI nesting going on.

-- 
Josh