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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EFC56C00144 for ; Fri, 29 Jul 2022 10:40:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235709AbiG2Kk1 convert rfc822-to-8bit (ORCPT ); Fri, 29 Jul 2022 06:40:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37284 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230264AbiG2Kk0 (ORCPT ); Fri, 29 Jul 2022 06:40:26 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 592EE19C1F for ; Fri, 29 Jul 2022 03:40:25 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-55-5dMw4K_ePdyLrUnYWn3eJw-1; Fri, 29 Jul 2022 11:40:22 +0100 X-MC-Unique: 5dMw4K_ePdyLrUnYWn3eJw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.36; Fri, 29 Jul 2022 11:40:20 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.036; Fri, 29 Jul 2022 11:40:20 +0100 From: David Laight To: 'Pawan Gupta' , Borislav Petkov CC: Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Dave Hansen , "x86@kernel.org" , "H. Peter Anvin" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , "tony.luck@intel.com" , "antonio.gomez.iglesias@linux.intel.com" , Daniel Sneddon , "andrew.cooper3@citrix.com" , Josh Poimboeuf Subject: RE: [RESEND RFC PATCH] x86/bugs: Add "unknown" reporting for MMIO Stale Data Thread-Topic: [RESEND RFC PATCH] x86/bugs: Add "unknown" reporting for MMIO Stale Data Thread-Index: AQHYovL4+baeEq2rDkCp4WwQq32ghq2VJ0xw Date: Fri, 29 Jul 2022 10:40:20 +0000 Message-ID: References: <20220729022851.mdj3wuevkztspodh@desk> In-Reply-To: <20220729022851.mdj3wuevkztspodh@desk> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Pawan Gupta > Sent: 29 July 2022 03:29 > > On Thu, Jul 28, 2022 at 02:00:13PM +0200, Borislav Petkov wrote: > > On Thu, Jul 14, 2022 at 06:30:18PM -0700, Pawan Gupta wrote: > > > Older CPUs beyond its Servicing period are not listed in the affected > > > processor list for MMIO Stale Data vulnerabilities. These CPUs currently > > > report "Not affected" in sysfs, which may not be correct. I looked this up.... The mitigations seem to rely on unprivileged code not being able to do MMIO accesses. That isn't true, device drivers can mmap PCIe addresses directly into user program address space. While unlikely, there is no reason this can't be supported for non-root processes. So if the underlying hardware doesn't correctly validate the byte enables then stale data can be read. It has to be said that I can't actually imagine getting anything useful unless you have co-operating processes using it as a security bypass side channel. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)