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 E22DFC433FE for ; Thu, 10 Mar 2022 14:54:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244353AbiCJOzs convert rfc822-to-8bit (ORCPT ); Thu, 10 Mar 2022 09:55:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245476AbiCJOjm (ORCPT ); Thu, 10 Mar 2022 09:39:42 -0500 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 313A2D4447 for ; Thu, 10 Mar 2022 06:32:51 -0800 (PST) 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-110-jc5_mpacNNeGF6-wP0QCGQ-1; Thu, 10 Mar 2022 14:32:48 +0000 X-MC-Unique: jc5_mpacNNeGF6-wP0QCGQ-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 15.0.1497.28; Thu, 10 Mar 2022 14:32:46 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.028; Thu, 10 Mar 2022 14:32:46 +0000 From: David Laight To: 'Bharata B Rao' , "linux-kernel@vger.kernel.org" CC: "linux-mm@kvack.org" , "x86@kernel.org" , "kirill.shutemov@linux.intel.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "shuah@kernel.org" , "oleg@redhat.com" , "ananth.narayan@amd.com" Subject: RE: [RFC PATCH v0 0/6] x86/AMD: Userspace address tagging Thread-Topic: [RFC PATCH v0 0/6] x86/AMD: Userspace address tagging Thread-Index: AQHYNHBEWuVw0etF4EmWwhK6DFJ++Ky4rWmQ Date: Thu, 10 Mar 2022 14:32:46 +0000 Message-ID: <699fb763ac054833bc8c29c9814c63b2@AcuMS.aculab.com> References: <20220310111545.10852-1-bharata@amd.com> In-Reply-To: <20220310111545.10852-1-bharata@amd.com> 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: linux-kernel@vger.kernel.org From: Bharata B Rao > Sent: 10 March 2022 11:16 > > This patchset makes use of Upper Address Ignore (UAI) feature available > on upcoming AMD processors to provide user address tagging support for x86/AMD. > > UAI allows software to store a tag in the upper 7 bits of a logical > address [63:57]. When enabled, the processor will suppress the > traditional canonical address checks on the addresses. More information > about UAI can be found in section 5.10 of 'AMD64 Architecture > Programmer's Manual, Vol 2: System Programming' which is available from > > https://bugzilla.kernel.org/attachment.cgi?id=300549 Is that really allowing bit 63 to be used? That is normally the user-kernel bit. I can't help feeling that will just badly break things. Otherwise the best thing is just to change access_ok() to only reject addresses with the top bit set. Then you shouldn't need any extra tests in the fast-path of access_ok(). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)