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Reply-To: alex.popov@linux.com
Subject: Re: [Cocci] Coccinelle rule for CVE-2019-18683
To:     Julia Lawall <julia.lawall@inria.fr>
Cc:     Gilles Muller <Gilles.Muller@lip6.fr>,
        Nicolas Palix <nicolas.palix@imag.fr>,
        Michal Marek <michal.lkml@markovi.net>, cocci@systeme.lip6.fr,
        "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Markus Elfring <Markus.Elfring@web.de>
References: <fff664e9-06c9-d2fb-738f-e8e591e09569@linux.com>
 <alpine.DEB.2.21.2004091248190.2403@hadrien>
From:   Alexander Popov <alex.popov@linux.com>
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Message-ID: <3c92523d-4b3f-e805-84e6-6abd1eedd683@linux.com>
Date:   Thu, 9 Apr 2020 22:56:57 +0300
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On 09.04.2020 13:53, Julia Lawall wrote:
> On Thu, 9 Apr 2020, Alexander Popov wrote:
>> virtual report
>>
>> @race exists@
>> expression E;
>> position stop_p;
>> position unlock_p;
>> position lock_p;
>> @@
>>
>> mutex_unlock@unlock_p(E)
>> ...
> 
> It would be good to put when != mutex_lock(E) after the ... above.  Your
> rule doesn't actually prevent the lock from being retaken.

Thanks Julia! I used this trick in the second version of the rule that I've just
sent.

>> kthread_stop@stop_p(...)
>> ...
>> mutex_lock@lock_p(E)
>>
>> @script:python@
>> stop_p << race.stop_p;
>> unlock_p << race.unlock_p;
>> lock_p << race.lock_p;
>> E << race.E;
>> @@
>>
>> coccilib.report.print_report(unlock_p[0], 'mutex_unlock(' + E + ') here')
>> coccilib.report.print_report(stop_p[0], 'kthread_stop here')
>> coccilib.report.print_report(lock_p[0], 'mutex_lock(' + E + ') here\n')

...

> Based on Jann's suggestion, it seem like it could be interesting to find
> these locking pauses, and then collect functions that are used in locks
> and in lock pauses.  If a function is mostly used with locks held, then
> using it in a lock pause could be a sign of a bug.  I will see if it turns
> up anything interesting.

Do you mean collecting the behaviour that happens between unlocking and locking
and then analysing it somehow?

Best regards,
Alexander