kernel-hardening - Re: [PATCH] time: Remove CONFIG_TIMER

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Date: Wed, 8 Feb 2017 11:24:01 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: John Stultz <john.stultz@...aro.org>
cc: Kees Cook <keescook@...omium.org>, Xing Gao <xgao01@...il.wm.edu>, 
    Jessica Frazelle <me@...sfraz.com>, 
    "Eric W. Biederman" <ebiederm@...ssion.com>, 
    Jonathan Corbet <corbet@....net>, Tejun Heo <tj@...nel.org>, 
    Lai Jiangshan <jiangshanlai@...il.com>, Petr Mladek <pmladek@...e.com>, 
    Andrew Morton <akpm@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, 
    Nicolas Iooss <nicolas.iooss_linux@....org>, 
    Nicolas Pitre <nicolas.pitre@...aro.org>, 
    Richard Cochran <richardcochran@...il.com>, 
    "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, 
    Michal Marek <mmarek@...e.com>, Josh Poimboeuf <jpoimboe@...hat.com>, 
    Dmitry Vyukov <dvyukov@...gle.com>, Olof Johansson <olof@...om.net>, 
    Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, 
    lkml <linux-kernel@...r.kernel.org>, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] time: Remove CONFIG_TIMER_STATS

On Tue, 7 Feb 2017, John Stultz wrote:
> On Tue, Feb 7, 2017 at 3:40 PM, Kees Cook <keescook@...omium.org> wrote:
> > Currently CONFIG_TIMER_STATS exposes process information across namespaces:
> >
> > kernel/time/timer_list.c print_timer():
> >
> >         SEQ_printf(m, ", %s/%d", tmp, timer->start_pid);
> >
> > /proc/timer_list:
> >
> >  #11: <0000000000000000>, hrtimer_wakeup, S:01, do_nanosleep, cron/2570
> >
> > Given that the tracer can give the same information, this patch entirely
> > removes CONFIG_TIMER_STATS.
> >
> > Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> I don't have an issue with this, but I worry this would break some
> tooling out there. Should it be marked as deprecated first?
> 
> Or maybe just pulling the band-aid off is the best way?

I think we should just kill it.

No tools can really rely on the behaviour of that file because it depends
on CONFIG_TIMER_STATS and the information available there is just a random
snapshot of queued timers at a given point of time, which is in no way
usefull.

Thanks,

	tglx

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