From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752832Ab3EARZz (ORCPT ); Wed, 1 May 2013 13:25:55 -0400 Received: from terminus.zytor.com ([198.137.202.10]:46072 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751051Ab3EARZr (ORCPT ); Wed, 1 May 2013 13:25:47 -0400 Message-ID: <518145F6.3060800@zytor.com> Date: Wed, 01 May 2013 09:42:30 -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> In-Reply-To: <20130501163404.GA6286@thunk.org> X-Enigmail-Version: 1.5.1 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 On 05/01/2013 09:34 AM, Theodore Ts'o wrote: > > In fact, there is the question of whether we should be checking to see > if the CPU stepping is one of the ones with the bug, and if so, to > have Linux disable fast strings even if the BIOS didn't, instead of > blindly enabling fast strings.... > 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. -hpa