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

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Message-Id: <1250690853.8282.59.camel@twins>
Date:	Wed, 19 Aug 2009 16:07:33 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.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, 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.

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



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