linux-kernel - Re: x86: warning in unwind_get_return

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Date:   Thu, 5 Jan 2017 09:17:00 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Kostya Serebryany <kcc@...gle.com>
Subject: Re: x86: warning in unwind_get_return_address

On Thu, Jan 05, 2017 at 03:59:52PM +0100, Dmitry Vyukov wrote:
> On Thu, Jan 5, 2017 at 3:49 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Tue, Dec 27, 2016 at 05:38:59PM +0100, Dmitry Vyukov wrote:
> >> On Thu, Dec 22, 2016 at 6:17 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> > On Wed, Dec 21, 2016 at 01:46:36PM +0100, Andrey Konovalov wrote:
> >> >> On Wed, Dec 21, 2016 at 12:36 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> >> >
> >> >> > 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?
> >> >>
> >> >> Sure, attached.
> >> >
> >> > Ok, I was able to recreate with your config.  The culprit was generated
> >> > code, as I suspected, though it wasn't BPF, it was a kprobe (created by
> >> > dccpprobe_init()).
> >> >
> >> > I'll make a patch to disable the warning.
> >>
> >> Hi,
> >>
> >> I am also seeing the following warnings:
> >>
> >> [  281.889259] WARNING: kernel stack regs at ffff8801c29a7ea8 in
> >> syz-executor8:1302 has bad 'bp' value ffff8801c29a7f28
> >> [  833.994878] WARNING: kernel stack regs at ffff8801c4e77ea8 in
> >> syz-executor1:13094 has bad 'bp' value ffff8801c4e77f28
> >>
> >> Can it also be caused by bpf/kprobe?
> >
> > This is a different warning.  I suspect it's due to unwinding the stack
> > of another CPU while it's running, which is still possible in a few
> > places.  I'm going to have to disable all these warnings for now.
> 
> 
> I also have the following diff locally. These loads trigger episodic
> KASAN warnings about stack-of-bounds reads on rcu stall warnings when
> it does backtrace of all cpus.
> If it looks correct to you, can you please also incorporate it into your patch?

Ok, will do.

BTW, I think there's an issue with your mail client.  Your last two
replies to me didn't have me on To/Cc.

-- 
Josh