From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755181Ab3EARgU (ORCPT ); Wed, 1 May 2013 13:36:20 -0400 Received: from terminus.zytor.com ([198.137.202.10]:46187 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755014Ab3EARgM (ORCPT ); Wed, 1 May 2013 13:36:12 -0400 Message-ID: <5181527A.8080904@zytor.com> Date: Wed, 01 May 2013 10:35:54 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 MIME-Version: 1.0 To: "Theodore Ts'o" , Borislav Petkov , Andy Lutomirski , linux-kernel@vger.kernel.org, x86@kernel.org, Andrew Lutomirski Subject: Re: [PATCH v5] x86: Enable fast strings on Intel if BIOS hasn't already References: <3cdeaedaa41e258e8aa9ca83d79a936e0b9462bc.1367385613.git.luto@amacapital.net> <20130501113352.GA29571@pd.tnic> <20130501163404.GA6286@thunk.org> <518145F6.3060800@zytor.com> <20130501172030.GA8609@thunk.org> In-Reply-To: <20130501172030.GA8609@thunk.org> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/01/2013 10:20 AM, Theodore Ts'o wrote: > On Wed, May 01, 2013 at 09:42:30AM -0700, H. Peter Anvin wrote: >> The erratum reads seriously, but it only affects crossings between pages >> of different page types, which is rare in itself. WT and WP are not >> even used in Linux; the UC case we end up doing 8-byte stores instead of >> the proper size, which is wrong, but for the case where the user is >> malicious the user could just do that directly, and it seems extremely >> hard to envision a scenario where someone would do that intentionally. > > Yeah, I wasn't so much worried about a malicious user as much as a > situation where the you're trying to debug a mysterious and > hard-to-reproduce failure, start tearing your hair out, and wondering > whether you're going insane or the compiler hates you and is out to > get you and you start staring at assembly code to try to figure out > how some piece of memory got mysteriously corrupted.... > If you are crossing pages with different memory types, the fact that the sizes being written are wrong is probably the least of your problems. -hpa