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From: John Stultz <john.stultz@linaro.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Arjan van de Ven <arjan@linux.intel.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Oren Laadan <orenl@cellrox.com>,
	Ruchi Kandoi <kandoiruchi@google.com>,
	Rom Lemarchand <romlem@android.com>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface
Date: Wed, 17 Feb 2016 12:51:17 -0800	[thread overview]
Message-ID: <CALAqxLVBgh2gZu1R8NguqoLjA+1VkHAraH5DguA3MTU2zNk0ig@mail.gmail.com> (raw)
In-Reply-To: <20160217121813.8a49986ebf66cedaf43e901b@linux-foundation.org>

On Wed, Feb 17, 2016 at 12:18 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Wed, 17 Feb 2016 12:09:08 -0800 Kees Cook <keescook@chromium.org> wrote:
>
>> On Wed, Feb 17, 2016 at 11:35 AM, Andrew Morton
>> <akpm@linux-foundation.org> wrote:
>> > On Tue, 16 Feb 2016 17:06:31 -0800 John Stultz <john.stultz@linaro.org> wrote:
>> >
>> >> This patch provides a proc/PID/timerslack_ns interface which
>> >> exposes a task's timerslack value in nanoseconds and allows it
>> >> to be changed.
>> >>
>> >> This allows power/performance management software to set timer
>> >> slack for other threads according to its policy for the thread
>> >> (such as when the thread is designated foreground vs. background
>> >> activity)
>> >>
>> >> If the value written is non-zero, slack is set to that value.
>> >> Otherwise sets it to the default for the thread.
>> >>
>> >> This interface checks that the calling task has permissions to
>> >> to use PTRACE_MODE_ATTACH_FSCREDS on the target task, so that we
>> >> can ensure arbitrary apps do not change the timer slack for other
>> >> apps.
>> >
>> > hm.  What the heck is PTRACE_MODE_ATTACH_FSCREDS and why was it chosen?
>>
>> This says the writer needs to have ptrace "attach" level of access,
>> and that it should be checked with fscreds, as is the standard for
>> most /proc things like that.
>
> The only place where PTRACE_MODE_ATTACH_FSCREDS is used in all of Linux
> is /prc/pid/stack.  Makes me curious!

Other uses may be using a combination PTRACE_MODE_ATTACH|PTRACE_MODE_FSCREDS.

>> > The procfs file's permissions are 0644, yes?  So a process's
>> > timer_slack is world-readable?  hm.
>>
>> This should be 600, IMO.
>
> Sounds safer.

Ok. Reworking the patch to use that as well.


Andrew: I saw you added these to -mm already. Would you prefer a fixup
patch ontop, or should I just send out a folded down v3 of the
patchset?

thanks
-john

  reply	other threads:[~2016-02-17 20:51 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-17  1:06 [PATCH 0/2] Extend timer_slack_ns to u64 on 32bit systems & add /proc/<pid>/timerslack_ns John Stultz
2016-02-17  1:06 ` [PATCH 1/2] timer: Convert timer_slack_ns from unsigned long to u64 John Stultz
2016-02-17  1:06 ` [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz
2016-02-17 19:35   ` Andrew Morton
2016-02-17 20:09     ` Kees Cook
2016-02-17 20:18       ` Andrew Morton
2016-02-17 20:51         ` John Stultz [this message]
2016-02-17 21:07           ` Andrew Morton
2016-02-17 22:29         ` John Stultz
2016-02-17 22:45           ` Kees Cook
2016-02-17 22:51             ` John Stultz
2016-02-17 22:53           ` Andrew Morton
2016-02-17 20:49     ` John Stultz
2016-02-18  5:59   ` [PATCH] proc: /proc/<pid>/timerslack_ns permissions fixes John Stultz
2016-02-18 17:52     ` Kees Cook
2016-07-13 23:47   ` [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz
2016-07-14  3:39     ` Kees Cook
2016-07-14  5:29       ` Arjan van de Ven
2016-07-14 12:48       ` Serge E. Hallyn
2016-07-14 13:42         ` Arjan van de Ven
2016-07-14 16:01           ` John Stultz
2016-07-14 16:09         ` John Stultz
2016-07-14 17:45           ` Kees Cook
2016-07-14 17:48             ` Arjan van de Ven
2016-07-14 17:49             ` Serge E. Hallyn
2016-07-14 17:56               ` Kees Cook
2016-07-14 20:21                 ` Serge E. Hallyn

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