Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756029AbaLKGg3 (ORCPT ); Thu, 11 Dec 2014 01:36:29 -0500 Received: from mail-wg0-f41.google.com ([74.125.82.41]:34643 "EHLO mail-wg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754440AbaLKGg1 (ORCPT ); Thu, 11 Dec 2014 01:36:27 -0500 Date: Thu, 11 Dec 2014 07:36:21 +0100 From: Ingo Molnar To: Andy Lutomirski Cc: Shaohua Li , "linux-kernel@vger.kernel.org" , X86 ML , kernel-team@fb.com, "H. Peter Anvin" , Ingo Molnar Subject: Re: [PATCH 3/3] X86: Add a thread cpu time implementation to vDSO Message-ID: <20141211063621.GC5059@gmail.com> References: <862cbb2ab71a9f71d1123b5512605350a4b61846.1418006970.git.shli@fb.com> <20141210215713.GA30230@devbig257.prn2.facebook.com> <20141210225627.GA11754@devbig257.prn2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andy Lutomirski wrote: > On Wed, Dec 10, 2014 at 2:56 PM, Shaohua Li 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 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 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/