From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 18 Dec 2013 10:59:29 +0100 (CET) Received: from mail-ea0-f179.google.com ([209.85.215.179]:35702 "EHLO mail-ea0-f179.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6826005Ab3LRJ7ZdXNLo (ORCPT ); Wed, 18 Dec 2013 10:59:25 +0100 Received: by mail-ea0-f179.google.com with SMTP id r15so3441673ead.24 for ; Wed, 18 Dec 2013 01:59:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=do5+sgkkGRf4RkRY64kPTOkpVJ/rS6QocStXkAO5/kM=; b=x7CczRJjJRxbs3T184GRp78xoHy6+6SgscvxcLq+GqjtMCF4IhB7eUb0w4QkNge0Pd HM2y480IT9rLfZuC9gvjYEJ3m5Xv+0YRFC2HKrkIYrU3zbwnqyqwRIykK/0tApRLvDas Jsv0SZK4tMrqZ2ltfA5GmEPQEA/71oHxEXv4nSWWKjcu4oVmQQmM7A8Mmh5DgrQyNSRG 4t/55voZKQOAFr0Br6JW0pk/V7HlO3Ombc8VWGm8CbAW6eTmej3KMwmc6vTDx+PqrKzN JYb6HZCIIMSmYKN72e9oCURbgkbapAFCH3pVOZyLcZVBu41xuOQKIqmKUobTgBmrGG3O eEjA== X-Received: by 10.15.43.10 with SMTP id w10mr28168462eev.13.1387360759700; Wed, 18 Dec 2013 01:59:19 -0800 (PST) Received: from gmail.com (BC24D856.catv.pool.telekom.hu. [188.36.216.86]) by mx.google.com with ESMTPSA id a51sm60922794eeh.8.2013.12.18.01.59.07 for (version=TLSv1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 18 Dec 2013 01:59:08 -0800 (PST) Date: Wed, 18 Dec 2013 10:59:05 +0100 From: Ingo Molnar To: Kees Cook Cc: linux-kernel@vger.kernel.org, Michal Marek , Russell King , Ralf Baechle , Paul Mundt , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Morton , James Hogan , Stephen Rothwell , Shawn Guo , x86@kernel.org, linux-kbuild@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux-sh@vger.kernel.org Subject: Re: [PATCH v3 2/2] provide -fstack-protector-strong build option Message-ID: <20131218095905.GB19319@gmail.com> References: <1387320194-24185-1-git-send-email-keescook@chromium.org> <1387320194-24185-3-git-send-email-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1387320194-24185-3-git-send-email-keescook@chromium.org> User-Agent: Mutt/1.5.21 (2010-09-15) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 38731 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: mingo@kernel.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips * Kees Cook wrote: > This changes the stack protector config option into a choice of "None", > "Regular", and "Strong". For "Strong", the kernel is built with > -fstack-protector-strong (gcc 4.9 and later). This options increases > the coverage of the stack protector without the heavy performance hit > of -fstack-protector-all. > > For reference, the stack protector options available in gcc are: > > -fstack-protector-all: > Adds the stack-canary saving prefix and stack-canary checking suffix to > _all_ function entry and exit. Results in substantial use of stack space > for saving the canary for deep stack users (e.g. historically xfs), and > measurable (though shockingly still low) performance hit due to all the > saving/checking. Really not suitable for sane systems, and was entirely > removed as an option from the kernel many years ago. > > -fstack-protector: > Adds the canary save/check to functions that define an 8 > (--param=ssp-buffer-size=N, N=8 by default) or more byte local char > array. Traditionally, stack overflows happened with string-based > manipulations, so this was a way to find those functions. Very few > total functions actually get the canary; no measurable performance or > size overhead. > > -fstack-protector-strong > Adds the canary for a wider set of functions, since it's not just those > with strings that have ultimately been vulnerable to stack-busting. With > this superset, more functions end up with a canary, but it still > remains small compared to all functions with no measurable change in > performance. Based on the original design document, a function gets the > canary when it contains any of: > - local variable's address used as part of the RHS of an assignment or > function argument > - local variable is an array (or union containing an array), regardless > of array type or length > - uses register local variables > https://docs.google.com/a/google.com/document/d/1xXBH6rRZue4f296vGt9YQcuLVQHeE516stHwt8M9xyU > > Comparison of "size" output when built with gcc-4.9 in three configurations: > - defconfig > - defconfig + CONFIG_CC_STACKPROTECTOR (+0.33%) > - defconfig + CONFIG_CC_STACKPROTECTOR_STRONG via this patch (+2.24%) > > text data bss dec hex filename > 11430641 1457584 1191936 14080161 d6d8a1 vmlinux > 11468490 1457584 1191936 14118010 d76c7a vmlinux.stackprotector > 11692790 1457584 1191936 14342310 dad8a6 vmlinux.stackprotector-strong Beyond the kernel size calculation, could you please also provide an estimation about the _number_ of functions affected, out of N kernel functions, so that the user has a rough picture about the scope and distribution of these variants? I.e. something like: # of canary checks .................................................................................. - defconfig 0 functions out of 100k functions - defconfig + STACKPROTECTOR 1k functions out of 100k functions - defconfig + STACKPROTECTOR_STRONG 20k functions out of 100k functions Thanks, Ingo