linux-kernel - Re: perf: fuzzer KASAN unwind_get_return

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Date:   Thu, 17 Nov 2016 08:01:50 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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>,
        Stephane Eranian <eranian@...il.com>
Subject: Re: perf: fuzzer KASAN unwind_get_return_address

On Thu, Nov 17, 2016 at 10:48:27AM +0100, Dmitry Vyukov wrote:
> Just in case, there is currently a known KASAN false positive related
> to longjmp's on GPFs. When a syscall hits GPF stack is unwound to
> kernel entry point, this leaves a bunch of stray poisoned redzones on
> the thread stack. They later cause false stack-out-of-bounds reports.
> 
> But this does not seem to be the case here. Kernel is not tainted. And
> shadow at the bottom of the reports looks sane.
> 
> But if that's the case somehow, we will need to add
> kasan_unpoison_remaining_stack() call before a longjmp like we did for
> jprobe_return():
> https://groups.google.com/d/msg/kasan-dev/Hzox58yZ4MU/TOdFoWMuBQAJ

I'm pretty sure this isn't a KASAN false positive.  The unwinder does
actually seem to be accessing a bad area of the stack, in the middle of
a function's stack frame.

-- 
Josh