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,URIBL_BLOCKED,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 0F036C43387 for ; Fri, 11 Jan 2019 01:34:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8CCF20879 for ; Fri, 11 Jan 2019 01:34:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729456AbfAKBeX (ORCPT ); Thu, 10 Jan 2019 20:34:23 -0500 Received: from mga01.intel.com ([192.55.52.88]:15757 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729329AbfAKBeW (ORCPT ); Thu, 10 Jan 2019 20:34:22 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Jan 2019 17:34:22 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,463,1539673200"; d="scan'208";a="290661265" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.154]) by orsmga005.jf.intel.com with ESMTP; 10 Jan 2019 17:34:21 -0800 Date: Thu, 10 Jan 2019 17:34:21 -0800 From: Sean Christopherson To: hpa@zytor.com Cc: Steven Rostedt , 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 , 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: <20190111013421.GD2365@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> <20190110174257.GE16556@linux.intel.com> <1955E727-BF68-4C00-A8C2-54FA9487A5A6@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1955E727-BF68-4C00-A8C2-54FA9487A5A6@zytor.com> 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 04:59:55PM -0800, hpa@zytor.com wrote: > On January 10, 2019 9:42:57 AM PST, Sean Christopherson wrote: > >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. > > If you run code from non-WB memory, all bets are off and you better > not be doing cross-modifying code. I wasn't thinking of running code from non-WB, but rather running code in WB while doing a CMC write via WC.