From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932453AbWGYEzq (ORCPT ); Tue, 25 Jul 2006 00:55:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932455AbWGYEzq (ORCPT ); Tue, 25 Jul 2006 00:55:46 -0400 Received: from [212.70.37.245] ([212.70.37.245]:13576 "EHLO raad.intranet") by vger.kernel.org with ESMTP id S932453AbWGYEzp (ORCPT ); Tue, 25 Jul 2006 00:55:45 -0400 From: Al Boldi To: Chuck Ebbert <76306.1226@compuserve.com> Subject: Re: [PATCH] x86: Don't randomize stack unless current->personality permits it Date: Tue, 25 Jul 2006 07:57:04 +0300 User-Agent: KMail/1.5 Cc: Paulo Marques , linux-kernel , Arjan van de Ven , Frank van Maarseveen References: <200607242023_MC3-1-C5FE-CADA@compuserve.com> In-Reply-To: <200607242023_MC3-1-C5FE-CADA@compuserve.com> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="windows-1256" Content-Transfer-Encoding: 7bit Message-Id: <200607250757.04664.a1426z@gawab.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Chuck Ebbert wrote: > On Mon, 24 Jul 2006 18:57:46 +0300, Al Boldi wrote: > > > With your changes on: > > > > > > stock kernel, randomize_va_space=0, gcc.322 -Os tstExec.c, > > > while :; do ./a.out; done > > > &x = 0xbffff874, &y = 0xbffff86c 28 28 > > > &x = 0xbffff874, &y = 0xbffff86c 27 27 > > > &x = 0xbffff874, &y = 0xbffff86c 27 27 > > > &x = 0xbffff874, &y = 0xbffff86c 28 27 > > > &x = 0xbffff874, &y = 0xbffff86c 27 30 > > > &x = 0xbffff874, &y = 0xbffff86c 27 29 > > > > > > stock kernel, randomize_va_space=1, gcc.322 -Os tstExec.c, > > > while :; do ./a.out; done > > > &x = 0xbfe2e614, &y = 0xbfe2e60c 29 28 > > > &x = 0xbfd6a104, &y = 0xbfd6a0fc 55 56 > > > &x = 0xbf91d454, &y = 0xbf91d44c 27 27 > > > &x = 0xbf941e84, &y = 0xbf941e7c 55 56 > > > &x = 0xbfa75834, &y = 0xbfa7582c 28 27 > > > &x = 0xbfb58634, &y = 0xbfb5862c 27 30 > > > > After closer inspection, it looks like addresses ending with 3c,7c,bc,fc > > cause a slowdown on P4, while addresses ending with > > 1c,3c,5c,7c,9c,bc,dc,fc cause a slowdown on P2. > > Those addresses cause 'y' to span a cacheline (P4 = 64 bytes, P2 = 32.) > Even when the kernel aligns to 128 bytes this could happen depending > on how deeply you nest functions. > > > Any easy way to instruct the kernel to skip those addresses? > > First, I think you need to define locals in order of decreasing size. > IOW 'x' and 'y' need to be first inside fn(), but that may not work > when things get inlined. So using the '-malign-double' GCC option, > or forcing alignment with '__attribute__ ((aligned(8)))' for each variable > might be better. > > Then you have to make sure the stack is aligned. See > '-mpreferred-stack-boundary'. This would imply a recompile, what about precompiled dists? Do they compile the sources this way? > I still think the kernel should be aligning the stack to 128 bytes anyway. I think so too, but can you see how randomization aggravates the situation? Thanks! -- Al