linux-kernel - Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread.

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Date:	Fri, 5 Feb 2016 12:44:04 -0800
From:	Kees Cook <keescook@...omium.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ruchi Kandoi <kandoiruchi@...gle.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oren Laadan <orenl@...lrox.com>,
	Rom Lemarchand <romlem@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack
 of an arbitrary thread.

On Fri, Feb 5, 2016 at 12:39 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Fri, Feb 5, 2016 at 12:32 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
>> On Fri, 5 Feb 2016 12:23:13 -0800 John Stultz <john.stultz@...aro.org> wrote:
>>> On Fri, Feb 5, 2016 at 12:13 PM, Andrew Morton
>>> <akpm@...ux-foundation.org> wrote:
>>>>
>>>> IOW, it would be more consistent to add sys_set_timer_slack()?
>>>
>>> I'm fine with moving this way.
>>>
>>> Ruchi/Rom: Any objections to that idea?
>>>
>>> Thomas/Arjan: Any other functionality we should consider including
>>> when adding a syscall to tweak timer slack?
>>
>> A syscall is quite a bit more fuss - implement it on x86_64, provide a
>> no-op default in sys_ni.c, add a test suite into
>> tools/testing/selftests (mainly for arch maintainers), wait for the
>> various arch maintainers to wire it up.
>
> Yea. It is. And I'm not excited to start over on this, but this
> functionality has already run into trouble in the Android tree, as the
> PR_SET_TIMERSLACK_PID value has hit multiple collisions over time.  So
> this functionality upstream would help resolve that pain.
>
>> Fortunately the build system now emits little messages which tell
>> maintainers that there's a new syscall which needs looking at.
>>
>> And a manpage will be needed, but a prctl manpage patch would have been
>> needed anyway.
>
> Yea.

Could this be exposed as a writable /proc entry instead? Like the oom_* stuff?

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security