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

[Andy Lutomirski]

On Sat, Nov 1, 2014 at 3:10 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Sat, 1 Nov 2014, Andy Lutomirski wrote:
>> On Nov 1, 2014 1:39 PM, "Thomas Gleixner" <tglx@xxxxxxxxxxxxx> 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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