Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754775AbZJUS7q (ORCPT ); Wed, 21 Oct 2009 14:59:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754030AbZJUS7q (ORCPT ); Wed, 21 Oct 2009 14:59:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:65012 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753934AbZJUS7p (ORCPT ); Wed, 21 Oct 2009 14:59:45 -0400 Message-ID: <4ADF59F8.7010205@redhat.com> Date: Wed, 21 Oct 2009 13:59:04 -0500 From: Eric Sandeen User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Arjan van de Ven CC: Ingo Molnar , Dave Jones , Linux Kernel , Thomas Gleixner , esandeen@redhat.com, cebbert@redhat.com, "H. Peter Anvin" Subject: Re: Unnecessary overhead with stack protector. References: <20091015183540.GA8098@redhat.com> <20091015190720.GA19467@elte.hu> <4ADF2DAA.9030604@redhat.com> <20091021110053.26ab9982@infradead.org> In-Reply-To: <20091021110053.26ab9982@infradead.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2540 Lines: 64 Arjan van de Ven wrote: > On Wed, 21 Oct 2009 10:50:02 -0500 > Eric Sandeen wrote: > >> Ingo Molnar wrote: >>> (Cc:-ed Arjan too.) >>> >>> * Dave Jones wrote: >>> >>>> 113c5413cf9051cc50b88befdc42e3402bb92115 introduced a change that >>>> made CC_STACKPROTECTOR_ALL not-selectable if someone enables >>>> CC_STACKPROTECTOR. >>>> >>>> We've noticed in Fedora that this has introduced noticable >>>> overhead on some functions, including those which don't even have >>>> any on-stack variables. >>>> >>>> According to the gcc manpage, -fstack-protector will protect >>>> functions with as little as 8 bytes of stack usage. So we're >>>> introducing a huge amount of overhead, to close a small amount of >>>> vulnerability (the >0 && <8 case). >>>> >>>> The overhead as it stands right now means this whole option is >>>> unusable for a distro kernel without reverting the above commit. >>> Exactly what workload showed overhead, and how much? >>> >>> Ingo >> I had xfs blowing up pretty nicely; granted, xfs is not svelte but it >> was never this bad before. >> > > do you have any indication that SP actually increases the stack > footprint by that much? it's only a few bytes.... > > Here's a sample of some of the largest xfs stack users, and the effect stack-protector had on them. This was just done with objdump -d xfs.ko | scripts/checkstack.pl; I don't know if there's extra runtime stack overhead w/ stackprotector? -Eric function nostack stackprot delta delta % xfs_bmapi 376 408 32 9% xfs_bulkstat 328 344 16 5% _xfs_trans_commit 296 312 16 5% xfs_iomap_write_delay 264 280 16 6% xfs_file_ioctl 248 312 64 26% xfs_symlink 248 264 16 6% xfs_bunmapi 232 280 48 21% xlog_do_recovery_pass 232 248 16 7% xfs_trans_unreserve_and_mod_sb 224 240 16 7% xfs_bmap_del_extent 216 248 32 15% xfs_cluster_write 216 232 16 7% xfs_file_compat_ioctl 216 296 80 37% xfs_attr_set_int 200 216 16 8% xfs_bmap_add_extent_delay_real 200 248 48 24% -- 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/