linux-kernel - Re: [PATCH v2 5/8] perf: Add pmu callbacks to track event mapping and unmapping

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Date:	Sun, 2 Nov 2014 12:15:29 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	X86 ML <x86@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"hillf.zj" <hillf.zj@...baba-inc.com>,
	Vince Weaver <vince@...ter.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Kees Cook <keescook@...omium.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>
Subject: Re: [PATCH v2 5/8] perf: Add pmu callbacks to track event mapping and unmapping

On Sat, Nov 1, 2014 at 3:10 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Sat, 1 Nov 2014, Andy Lutomirski wrote:
>> On Nov 1, 2014 1:39 PM, "Thomas Gleixner" <tglx@...utronix.de> wrote:
>> > On Sat, 1 Nov 2014, Andy Lutomirski wrote:
>> > > There's plenty of room to tighten up the restrictions further, but
>> > > this is, I think, a decent first step, and it solves the problem of
>> > > information leaking into seccomp sandboxes.
>> >
>> > In which way?
>>
>> All the performance counters were readable without using any syscalls.
>> That leaks hints as to which events are in use, and it possibly leaks
>> interesting side channel information.   With this series applied, you
>> need a at least mmap an rdpmc-able event, which most seccomp sandboxes
>> won't allow.
>
> Ok. So you are preventing the seccomp sandboxes to open/mmap a counter.
>

Yes.

Conversely, if someone lets perf_event_open through a seccomp filter,
then the sandboxed code can probably gather more interesting
information using perf_event_open the normal way than they can by
poking at rdpmc.

--Andy

>> Unfortunately, rdpmc access to counters can't be controlled
>> individually, so it's hard to do all that much better than this.
>
> Yeah, I know ...
>
> Thanks,
>
>         tglx



-- 
Andy Lutomirski
AMA Capital Management, LLC
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