Messages in this thread | | | Date | Thu, 11 Dec 2014 07:36:21 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] X86: Add a thread cpu time implementation to vDSO |
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* Andy Lutomirski <luto@amacapital.net> wrote:
> On Wed, Dec 10, 2014 at 2:56 PM, Shaohua Li <shli@fb.com> wrote: > > On Wed, Dec 10, 2014 at 02:13:23PM -0800, Andy Lutomirski wrote: > >> On Wed, Dec 10, 2014 at 1:57 PM, Shaohua Li <shli@fb.com> wrote: > >> > On Wed, Dec 10, 2014 at 11:10:52AM -0800, Andy Lutomirski wrote: > >> >> On Sun, Dec 7, 2014 at 7:03 PM, Shaohua Li <shli@fb.com> wrote: > >> >> > This primarily speeds up clock_gettime(CLOCK_THREAD_CPUTIME_ID, ..). We > >> >> > use the following method to compute the thread cpu time: > >> >> > >> >> I like the idea, and I like making this type of profiling fast. I > >> >> don't love the implementation because it's an information leak (maybe > >> >> we don't care) and it's ugly. > >> >> > >> >> The info leak could be fixed completely by having a per-process array > >> >> instead of a global array. That's currently tricky without wasting > >> >> memory, but it could be created on demand if we wanted to do that, > >> >> once my vvar .fault patches go in (assuming they do -- I need to ping > >> >> the linux-mm people). > >> > > >> > those info leak really doesn't matter. > >> > >> Why not? > > > > Ofcourse I can't make sure completely, but how could this > > info be used as attack? > > It may leak interesting timing info, even from cpus that are > outside your affinity mask / cpuset. I don't know how much > anyone actually cares.
Finegraned timing information has been successfully used to recover secret keys (and sometimes even coarse timing information), so it can be a security issue in certain setups.
Thanks,
Ingo
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