linux-kernel - Re: yama: lockdep warning on yama_ptracer

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Message-ID: <CAGXu5j+XuQxJcUWSNaziMivNjKsB9S9cFMKDbigCBN16NGBRgw@mail.gmail.com>
Date:	Mon, 19 Nov 2012 08:23:30 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>, james.l.morris@...cle.com,
	John Johansen <john.johansen@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-security-module@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: yama: lockdep warning on yama_ptracer_del

On Sun, Nov 18, 2012 at 8:05 PM, Sasha Levin <levinsasha928@...il.com> wrote:
> Hi Kees,
>
> On Thu, Oct 18, 2012 at 6:39 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Wed, Oct 17, 2012 at 8:10 PM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>> Hi all,
>>>
>>> I was fuzzing with trinity within a KVM tools guest (lkvm) on a linux-next kernel, and got the
>>> following dump which I believe to be noise due to how the timers work - but I'm not 100% sure.
>>> ...
>>> [  954.674123]  Possible interrupt unsafe locking scenario:
>>> [  954.674123]
>>> [  954.674123]        CPU0                    CPU1
>>> [  954.674123]        ----                    ----
>>> [  954.674123]   lock(ptracer_relations_lock);
>>> [  954.674123]                                local_irq_disable();
>>> [  954.674123]                                lock(&(&new_timer->it_lock)->rlock);
>>> [  954.674123]                                lock(ptracer_relations_lock);
>>> [  954.674123]   <Interrupt>
>>> [  954.674123]     lock(&(&new_timer->it_lock)->rlock);
>>> [  954.674123]
>>> [  954.674123]  *** DEADLOCK ***
>>
>> I've been wanting to get rid of the Yama ptracer_relations_lock
>> anyway, so maybe I should do that now just to avoid this case at all?
>
> I still see this one in -rc6, is there anything to get rid of it
> before the release?

I'm not sure about changes to the timer locks, but I haven't been able
to get rid of the locking on Yama's task_free path. I did send a patch
to get rid of locking during a read, though:

https://lkml.org/lkml/2012/11/13/808

-Kees

-- 
Kees Cook
Chrome OS Security
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