Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932102AbeAHLqN (ORCPT + 1 other); Mon, 8 Jan 2018 06:46:13 -0500 Received: from www.llwyncelyn.cymru ([82.70.14.225]:32898 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756301AbeAHLqJ (ORCPT ); Mon, 8 Jan 2018 06:46:09 -0500 Date: Mon, 8 Jan 2018 11:43:42 +0000 From: Alan Cox To: Peter Zijlstra Cc: Dan Williams , "Eric W. Biederman" , Linux Kernel Mailing List , Mark Rutland , Alan Cox , Srinivas Pandruvada , Will Deacon , Solomon Peachy , "H. Peter Anvin" , Christian Lamparter , Elena Reshetova , linux-arch@vger.kernel.org, Andi Kleen , "James E.J. Bottomley" , linux-scsi , Jonathan Corbet , X86 ML , Ingo Molnar , Alexey Kuznetsov , Zhang Rui , "Linux-media@vger.kernel.org" , Arnd Bergmann , Jan Kara , Eduardo Valentin , Al Viro , qla2xxx-upstream@qlogic.com, Thomas Gleixner , Mauro Carvalho Chehab , Arjan van de Ven , Kalle Valo , Alan Cox , "Martin K. Petersen" , Hideaki YOSHIFUJI , Greg KH , linux-wireless@vger.kernel.org, Netdev , Linus Torvalds , "David S. Miller" , Laurent Pinchart Subject: Re: [PATCH 00/18] prevent bounds-check bypass via speculative execution Message-ID: <20180108114342.3b2d99fb@alans-desktop> In-Reply-To: <20180108100836.GF3040@hirez.programming.kicks-ass.net> References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com> <87y3lbpvzp.fsf@xmission.com> <20180108100836.GF3040@hirez.programming.kicks-ass.net> Organization: Intel Corporation X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Mon, 8 Jan 2018 11:08:36 +0100 Peter Zijlstra wrote: > On Fri, Jan 05, 2018 at 10:30:16PM -0800, Dan Williams wrote: > > On Fri, Jan 5, 2018 at 6:22 PM, Eric W. Biederman wrote: > > > In at least one place (mpls) you are patching a fast path. Compile out > > > or don't load mpls by all means. But it is not acceptable to change the > > > fast path without even considering performance. > > > > Performance matters greatly, but I need help to identify a workload > > that is representative for this fast path to see what, if any, impact > > is incurred. Even better is a review that says "nope, 'index' is not > > subject to arbitrary userspace control at this point, drop the patch." > > I think we're focussing a little too much on pure userspace. That is, we > should be saying under the attackers control. Inbound network packets > could equally be under the attackers control. Inbound network packets don't come with a facility to read back and do cache timimg. For the more general case, timing attacks on network activity are not exactly new, and you have to mitigate them in user space because most of them are about how many instructions you execute on each path. The ancient classic being telling if a user exists by seeing if the password was actually checked. Alan