From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752423Ab3KNBTj (ORCPT ); Wed, 13 Nov 2013 20:19:39 -0500 Received: from mail-pa0-f44.google.com ([209.85.220.44]:41208 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750889Ab3KNBTc (ORCPT ); Wed, 13 Nov 2013 20:19:32 -0500 Date: Wed, 13 Nov 2013 17:19:29 -0800 From: Guenter Roeck To: "H. Peter Anvin" Cc: Kees Cook , Andrew Morton , linux-kernel@vger.kernel.org, Jan Beulich Subject: Re: [PATCH] gcc4: Disable __compiletime_object_size for GCC 4.6+ Message-ID: <20131114011929.GA13835@roeck-us.net> References: <1365821348-7177-1-git-send-email-linux@roeck-us.net> <20131113183913.GK4994@outflux.net> <5283E7A9.6090706@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5283E7A9.6090706@zytor.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 13, 2013 at 12:57:13PM -0800, H. Peter Anvin wrote: > On 11/13/2013 10:39 AM, Kees Cook wrote: > > Hi Guenter, > > > > On Fri, Apr 12, 2013 at 07:49:08PM -0700, Guenter Roeck wrote: > >> __builtin_object_size is known to be broken on gcc 4.6+. > >> See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48880 for details. > >> > >> This causes unnecssary build warnings and errors such as > >> > >> In function 'copy_from_user', inlined from 'sb16_copy_from_user' > >> at sound/oss/sb_audio.c:878:22: > >> arch/x86/include/asm/uaccess_32.h:211:26: error: call to 'copy_from_user_overflow' > >> declared with attribute error: copy_from_user() buffer size is not provably correct > >> make[3]: [sound/oss/sb_audio.o] Error 1 (ignored) > >> > >> Disable it where broken. > > > > Is there an alternative? This means that things like > > DEBUG_STRICT_USER_COPY_CHECKS are being rendered useless. I don't think > > this is _always_ broken, just under certain situations, right? > > > > It would be one thing to block it for, say, gcc 4.6 and 4.7 only, but > without an upper cap I don't think this is at all okay. > Also please have a look into https://lkml.org/lkml/2013/10/21/52. That patch has been accepted (3df7b41aa5e); maybe above commit (2fb0815c9) is now unnecessary and can be reverted. I don't know about parisc (Jan was concerned about that), but at least on x86 I don't see above warning anymore after reverting my patch. Guenter