From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6DA23C43387 for ; Thu, 10 Jan 2019 17:43:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 408BB20657 for ; Thu, 10 Jan 2019 17:43:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730804AbfAJRm7 (ORCPT ); Thu, 10 Jan 2019 12:42:59 -0500 Received: from mga04.intel.com ([192.55.52.120]:44801 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730425AbfAJRm6 (ORCPT ); Thu, 10 Jan 2019 12:42:58 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Jan 2019 09:42:57 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,462,1539673200"; d="scan'208";a="107264129" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.154]) by orsmga006.jf.intel.com with ESMTP; 10 Jan 2019 09:42:57 -0800 Date: Thu, 10 Jan 2019 09:42:57 -0800 From: Sean Christopherson To: Steven Rostedt Cc: Josh Poimboeuf , Nadav Amit , X86 ML , LKML , Ard Biesheuvel , Andy Lutomirski , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Masami Hiramatsu , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov , Julia Cartwright , Jessica Yu , "H. Peter Anvin" , Rasmus Villemoes , Edward Cree , Daniel Bristot de Oliveira Subject: Re: [PATCH v3 5/6] x86/alternative: Use a single access in text_poke() where possible Message-ID: <20190110174257.GE16556@linux.intel.com> References: <279b8003f7f0a6831d090ab822d37bc958f974de.1547073843.git.jpoimboe@redhat.com> <8138A1EE-359D-4CD2-8E96-5BF00313AB3B@vmware.com> <20190110172004.wuh45xoafynfm2df@treble> <20190110123243.3b9e0856@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190110123243.3b9e0856@gandalf.local.home> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 10, 2019 at 12:32:43PM -0500, Steven Rostedt wrote: > On Thu, 10 Jan 2019 11:20:04 -0600 > Josh Poimboeuf wrote: > > > > > While I can't find a reason for hypervisors to emulate this instruction, > > > smarter people might find ways to turn it into a security exploit. > > > > Interesting point... but I wonder if it's a realistic concern. BTW, > > text_poke_bp() also relies on undocumented behavior. > > But we did get an official OK from Intel that it will work. Took a bit > of arm twisting to get them to do so, but they did. And it really is > pretty robust. Did we (they?) list any caveats for this behavior? E.g. I'm fairly certain atomicity guarantees go out the window if WC memtype is used.