Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755622AbeAHSeC (ORCPT + 1 other); Mon, 8 Jan 2018 13:34:02 -0500 Received: from mail-wr0-f174.google.com ([209.85.128.174]:38159 "EHLO mail-wr0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755541AbeAHSdn (ORCPT ); Mon, 8 Jan 2018 13:33:43 -0500 X-Google-Smtp-Source: ACJfBosgqbBXyq0HAEBR/63DuZSUuZO9f+aLUjvUnpn5pLGNhLgYR6Sd92qHcFjMiIkLOefMt8r2Vg== Date: Mon, 8 Jan 2018 19:33:37 +0100 From: Ingo Molnar To: Alan Cox Cc: Peter Zijlstra , 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: <20180108183337.iq7xjxf2dkbkzig6@gmail.com> References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com> <87y3lbpvzp.fsf@xmission.com> <20180108100836.GF3040@hirez.programming.kicks-ass.net> <20180108114342.3b2d99fb@alans-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180108114342.3b2d99fb@alans-desktop> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: * Alan Cox wrote: > 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. [...] But the reply packets can be measured on the sending side, and the total delay timing would thus carry the timing information. Yes, a lot of noise gets added that way if we think 'packet goes through the Internet' - but with gigabit local network access or even through localhost access a lot of noise can be removed as well. It's not as dangerous as a near instantaneous local attack, but 'needs a day of runtime to brute-force through localhost or 10GigE' is still worrying in many real-world security contexts. So I concur with Peter that we should generally consider making all of our responses to external data (maybe with the exception of pigeon post messages) Spectre-safe. Thanks, Ingo