Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754797Ab0FSIVc (ORCPT ); Sat, 19 Jun 2010 04:21:32 -0400 Received: from one.firstfloor.org ([213.235.205.2]:59102 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754665Ab0FSIVb (ORCPT ); Sat, 19 Jun 2010 04:21:31 -0400 From: Andi Kleen To: Kees Cook Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Alexander Potashev , Tim Abbott , Sam Ravnborg , Jan Beulich , Jeremy Fitzhardinge , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/4] x86: clear XD_DISABLED flag on Intel to regain NX References: <20100619055010.GR24749@outflux.net> Date: Sat, 19 Jun 2010 10:21:29 +0200 In-Reply-To: <20100619055010.GR24749@outflux.net> (Kees Cook's message of "Fri, 18 Jun 2010 22:50:10 -0700") Message-ID: <874ogzph4m.fsf@basil.nowhere.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1089 Lines: 30 Kees Cook writes: > This will clear the MSR_IA32_MISC_ENABLE_XD_DISABLE bit so that NX cannot > be inappropriately controlled by the BIOS on Intel CPUs. If NX actually > needs to be disabled, "noexec=off" can be used. The patch still seems like a bad idea to me. What happens if the NX bit is broken for some reason and the BIOS is right to disable it? If there's some VM which doesn't ignore unknown MSR writes it could also break early, and at best you get an ugly message and at worst a crash. Do you have evidence for a lot of systems where NX is disabled this way without BIOS option? Really such information should be in the patch description. If you really need to apply it apply it in some place where exception handling is possible at least. -Andi -- ak@linux.intel.com -- Speaking for myself only. -- 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/