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Date: Tue, 20 Dec 2016 17:36:40 -0600
From: Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: x86: warning in unwind_get_return_address
Message-ID: <20161220233640.pc4goscldmpkvtqa@treble>
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To: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, kasan-dev <kasan-dev@googlegroups.com>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, Kostya Serebryany <kcc@google.com>, syzkaller <syzkaller@googlegroups.com>

On Tue, Dec 20, 2016 at 11:35:23PM +0100, Andrey Konovalov wrote:
> On Tue, Dec 20, 2016 at 10:01 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > On Tue, Dec 20, 2016 at 03:43:27PM +0100, Andrey Konovalov wrote:
> >> Hi,
> >>
> >> I've got the following warning while running the syzkaller fuzzer:
> >>
> >> WARNING: unrecognized kernel stack return address ffffffffa0000001 at
> >> ffff88006377fa18 in a.out:4467
> >>
> >> By adding a BUG() to unwind_get_return_address() I was able to capture
> >> the stack trace (see below). Looks like unwind_get_return_address()
> >> gets called when KASAN tries to unwind the stack to save the stack
> >> trace.
> >>
> >> A reproducer is attached. CONFIG_KASAN=y is most likely needed for it to work.
> >
> > Hi Andrey,
> >
> > I've tried with your reproducer but it didn't recreate.  Can you try
> > again with the following patch from the tip tree, instead of your BUG()
> > patch?
> >
> >   http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/patch/?id=8b5e99f02264130782a10ba5c0c759797fb064ee
> >
> > That will dump the stack data, which should give more clues about what
> > went wrong.
> 
> Hi Josh,
> 
> Sure, here it is:

Thanks.  Looking at the stack trace, my guess is that an interrupt hit
while running in generated BPF code, and the unwinder got confused
because regs->ip points to the generated code.  I may need to disable
that warning until we figure out a better solution.

Can you share your .config file?

-- 
Josh

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