Re: [PATCH] x86,seccomp,prctl: Remove PR_TSC_SIGSEGV and seccomp TSC filtering

[Andy Lutomirski]

On Fri, Oct 3, 2014 at 2:12 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Fri, Oct 03, 2014 at 02:04:53PM -0700, Andy Lutomirski wrote:
>> On Fri, Oct 3, 2014 at 2:02 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
>> > Something like so.. slightly less ugly and possibly with more
>> > complicated conditions setting the cr4 if you want to fix tsc vs seccomp
>> > as well.
>>
>> This will crash anything that tries rdpmc in an allow-everything
>> seccomp sandbox.  It's also not very compatible with my grand scheme
>> of allowing rdtsc to be turned off without breaking clock_gettime. :)
>
> Well, we clear cap_user_rdpmc, so everybody who still tries it gets what
> he deserves, no problem there.

Oh, interesting.

To continue playing devil's advocate, what if you do perf_event_open,
then mmap it, then start the seccomp sandbox?

My draft patches are currently tracking the number of perf_event mmaps
per mm.  I'm not thrilled with it, but it's straightforward.  And I
still need to benchmark cr4 writes, which is tedious, because I can't
do it from user code.

--Andy
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