Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751301AbeAEFLZ (ORCPT + 1 other); Fri, 5 Jan 2018 00:11:25 -0500 Received: from mga01.intel.com ([192.55.52.88]:51978 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbeAEFLY (ORCPT ); Fri, 5 Jan 2018 00:11:24 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,317,1511856000"; d="scan'208";a="189954495" Subject: Re: [PATCH 3/7] x86/enter: Use IBRS on syscall and interrupts To: Andy Lutomirski References: <0c525c4c6c817e9c42c7ed583d86dc591a86efde.1515086770.git.tim.c.chen@linux.intel.com> <20180104223321.GD32035@hirez.programming.kicks-ass.net> <8e382c5a-1d8d-44e6-87f4-176305493a47@intel.com> Cc: Peter Zijlstra , Tim Chen , Thomas Gleixner , Linus Torvalds , Greg KH , Andrea Arcangeli , Andi Kleen , Arjan Van De Ven , LKML From: Dave Hansen Message-ID: <84a6f2f2-d5fe-6b42-0590-33723c1b4960@intel.com> Date: Thu, 4 Jan 2018 21:11:23 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On 01/04/2018 08:51 PM, Andy Lutomirski wrote: > Do we need an arch_prctl() to enable IBRS for user mode? Eventually, once the dust settles. I think there's a spectrum of paranoia here, that is roughly (with increasing paranoia): 1. do nothing 2. do retpoline 3. do IBRS in kernel 4. do IBRS always I think you're asking for ~3.5. Patches for 1-3 are out there and 4 is pretty straightforward. Doing a arch_prctl() is still straightforward, but will be a much more niche thing than any of the other choices. Plus, with a user interface, we have to argue over the ABI for at least a month or two. ;)