Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753107AbeAFMeR (ORCPT + 1 other); Sat, 6 Jan 2018 07:34:17 -0500 Received: from www.llwyncelyn.cymru ([82.70.14.225]:55054 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752895AbeAFMeP (ORCPT ); Sat, 6 Jan 2018 07:34:15 -0500 Date: Sat, 6 Jan 2018 12:32:42 +0000 From: Alan Cox To: Linus Torvalds Cc: Dan Williams , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Andi Kleen , Arnd Bergmann , Greg Kroah-Hartman , Peter Zijlstra , Network Development , "the arch/x86 maintainers" , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner Subject: Re: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok Message-ID: <20180106123242.77f4d860@alans-desktop> In-Reply-To: References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com> <151520102670.32271.8447983009852138826.stgit@dwillia2-desk3.amr.corp.intel.com> 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 Fri, 5 Jan 2018 18:52:07 -0800 Linus Torvalds wrote: > On Fri, Jan 5, 2018 at 5:10 PM, Dan Williams wrote: > > From: Andi Kleen > > > > When access_ok fails we should always stop speculating. > > Add the required barriers to the x86 access_ok macro. > > Honestly, this seems completely bogus. Also for x86-64 if we are trusting that an AND with a constant won't get speculated into something else surely we can just and the address with ~(1 << 63) before copying from/to user space ? The user will then just speculatively steal their own memory. Alan