linux-kernel - Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement fast refcount overflow protection

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Date:   Tue, 29 Aug 2017 08:39:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mike Galbraith <efault@....de>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Arnd Bergmann <arnd@...db.de>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement
 fast refcount overflow protection

On Tue, Aug 29, 2017 at 3:03 AM, Mike Galbraith <efault@....de> wrote:
> On Tue, 2017-08-29 at 11:27 +0200, Ingo Molnar wrote:
>> * Mike Galbraith <efault@....de> wrote:
>>
>> > On Tue, 2017-08-29 at 10:58 +0200, Ingo Molnar wrote:
>> > > * Mike Galbraith <efault@....de> wrote:
>> > >
>> > > > Greetings,
>> > > >
>> > > > Take 2 of KVM bisect as you work fingered $subject.  Take 1 was stymied
>> > > > by build dependencies (aa5d1b81, df340524) which I foolishly tried to
>> > > > skip, leading git bisect to end up handing me a list of commits that
>> > > > might be busted.  During take 2, I added those two as required.
>> > > >
>> > > > Symptom is a few splats as below, with box finally hanging.  Network
>> > > > comes up, but neither ssh nor console login is possible.
>> > >
>> > > Just to double check, does the patch below also cure the regression?
>> > > If we don't find the bug it might be safer than a full revert.
>> >
>> > I reverted it, and vbox now boots.  Should I still try the below?
>>
>> Would be nice, so I can stick a Tested-by on it and such!
>
> Done, works.

Was this the x86 refcount implementation, or a atomic -> refcount conversion?

-Kees

-- 
Kees Cook
Pixel Security