linux-kernel - Re: [PATCH 1/4] perf_counter: Default to higher paranoia level

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Date:	Wed, 19 Aug 2009 18:04:39 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>,
	James Morris <jmorris@...ei.org>
Subject: Re: [PATCH 1/4] perf_counter: Default to higher paranoia level

On Wed, Aug 19, 2009 at 04:07:33PM +0200, Peter Zijlstra wrote:
> On Wed, 2009-08-19 at 11:18 +0200, Peter Zijlstra wrote:
> 
> > +static inline bool perf_paranoid_anon(void)
> > +{
> > +	return !capable(CAP_SYS_ADMIN) && sysctl_perf_counter_paranoid > 1;
> >  }
> >  
> >  static inline bool perf_paranoid_kernel(void)
> >  {
> > -	return sysctl_perf_counter_paranoid > 1;
> > +	return !capable(CAP_SYS_ADMIN) && sysctl_perf_counter_paranoid > 2;
> > +}
> 
> OK, this is buggy:
> 
>  - capable() uses current, which is unlikely to be counter->owner,
>  - but even security_real_capable(counter->owner, ...) wouldn't
>    work, since the ->capable() callback isn't NMI safe
>    (selinux takes locks and does allocations in that path).
> 
> This puts a severe strain on more complex anonymizers since its
> basically impossible to tell if counter->owner has permissions on
> current from NMI context.
> 
> I'll fix up this patch to pre-compute the perf_paranoid_anon_ip() per
> counter based on creation time state, unless somebody has a better idea.


Something I don't understand there: it's about wide per cpu profiling,
then the task that have been created before the counter can also be
profiled, then how is the creation time useful here?



> I could possibly only anonymize IRQ context (SoftIRQ context is
> difficult since in_softirq() means both in-softirq and
> softirq-disabled).


I don't understand why we need to set this paranoid level concerning
kernel RIPS.

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