Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751226AbeADXYX (ORCPT + 1 other); Thu, 4 Jan 2018 18:24:23 -0500 Received: from www.llwyncelyn.cymru ([82.70.14.225]:48070 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751029AbeADXYW (ORCPT ); Thu, 4 Jan 2018 18:24:22 -0500 Date: Thu, 4 Jan 2018 23:24:11 +0000 From: Alan Cox To: Tony Luck Cc: Alexander Kleinsorge , Linux Kernel Mailing List Subject: Re: proposal for meltdown-workaround with low overhead Message-ID: <20180104232411.17c21652@alans-desktop> In-Reply-To: References: <9f274ca7-732d-810a-4e51-83309b96d14b@physik.tu-berlin.de> 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 Thu, 4 Jan 2018 15:09:28 -0800 Tony Luck wrote: > On Thu, Jan 4, 2018 at 11:45 AM, Alexander Kleinsorge > wrote: > > As Meltdown-Issue depends on allowing to cause many exceptions (usually : > > accessing an invalid address), we could restrict this misusage easy. > > The accesses to the invalid address are performed speculatively by the CPU in > a code branch that is later found to be not taken. Hence there are no exceptions > at all. Actually for the 'spectre' attack you can sometimes see hints because many of the obvious attack points end up causing a syscall to return an errno value. One thing that might be interesting for the paranoid is indeed to react to some of those (notably EINVAL, EFAULT) by stirring up the mud before that process runs again. Alan