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 C207AC0015E for ; Tue, 15 Aug 2023 15:24:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237950AbjHOPYU convert rfc822-to-8bit (ORCPT ); Tue, 15 Aug 2023 11:24:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236518AbjHOPX5 (ORCPT ); Tue, 15 Aug 2023 11:23:57 -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 ESMTPS id 6645E9C for ; Tue, 15 Aug 2023 08:23:56 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-47-n93EMhJ-NZikTdM6_6FSgA-1; Tue, 15 Aug 2023 16:23:54 +0100 X-MC-Unique: n93EMhJ-NZikTdM6_6FSgA-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Tue, 15 Aug 2023 16:23:51 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Tue, 15 Aug 2023 16:23:51 +0100 From: David Laight To: 'Stefan Hajnoczi' , "kvm@vger.kernel.org" CC: Jason Gunthorpe , "Tian, Kevin" , "linux-kernel@vger.kernel.org" , "Alex Williamson" Subject: RE: [PATCH 2/4] vfio: use __aligned_u64 in struct vfio_device_gfx_plane_info Thread-Topic: [PATCH 2/4] vfio: use __aligned_u64 in struct vfio_device_gfx_plane_info Thread-Index: AQHZywUc1n/Y7EJLKUyoxnVRLesskK/rgeRQ Date: Tue, 15 Aug 2023 15:23:50 +0000 Message-ID: References: <20230809210248.2898981-1-stefanha@redhat.com> <20230809210248.2898981-3-stefanha@redhat.com> In-Reply-To: <20230809210248.2898981-3-stefanha@redhat.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 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: kvm@vger.kernel.org From: Stefan Hajnoczi > Sent: 09 August 2023 22:03 > > The memory layout of struct vfio_device_gfx_plane_info is > architecture-dependent due to a u64 field and a struct size that is not > a multiple of 8 bytes: > - On x86_64 the struct size is padded to a multiple of 8 bytes. > - On x32 the struct size is only a multiple of 4 bytes, not 8. > - Other architectures may vary. > > Use __aligned_u64 to make memory layout consistent. This reduces the > chance of holes that result in an information leak and the chance that > 32-bit userspace on a 64-bit kernel breakage. Isn't the hole likely to cause an information leak? Forcing it to be there doesn't make any difference. I'd add an explicit pad as well. It is a shame there isn't an __attribute__(()) to error padded structures. > > This patch increases the struct size on x32 but this is safe because of > the struct's argsz field. The kernel may grow the struct as long as it > still supports smaller argsz values from userspace (e.g. applications > compiled against older kernel headers). Doesn't changing the offset of later fields break compatibility? The size field (probably) only lets you extend the structure. Oh, for sanity do min(variable, constant). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)