From patchwork Tue Jun 14 15:05:37 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefano Stabellini X-Patchwork-Id: 635405 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3rTYsW04Z6z9s9Y for ; Wed, 15 Jun 2016 01:46:23 +1000 (AEST) Received: from localhost ([::1]:36259 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCqXk-0001mH-Uz for incoming@patchwork.ozlabs.org; Tue, 14 Jun 2016 11:46:21 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34144) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCpuZ-000433-6T for qemu-devel@nongnu.org; Tue, 14 Jun 2016 11:05:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bCpuU-0006E7-5O for qemu-devel@nongnu.org; Tue, 14 Jun 2016 11:05:51 -0400 Received: from mail.kernel.org ([198.145.29.136]:54198) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCpuT-0006DJ-Ga for qemu-devel@nongnu.org; Tue, 14 Jun 2016 11:05:45 -0400 Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 5CF86201BB; Tue, 14 Jun 2016 15:05:44 +0000 (UTC) Received: from localhost.localdomain (60.99.208.46.dyn.plus.net [46.208.99.60]) (using TLSv1.2 with cipher AES128-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1DA0D201F4; Tue, 14 Jun 2016 15:05:41 +0000 (UTC) From: Stefano Stabellini To: peter.maydell@linaro.org Date: Tue, 14 Jun 2016 16:05:37 +0100 Message-Id: <1465916738-15687-1-git-send-email-sstabellini@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: References: X-Virus-Scanned: ClamAV using ClamSMTP X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 198.145.29.136 Subject: [Qemu-devel] [PULL 1/2] xen/blkif: avoid double access to any shared ring request fields X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: anthony.perard@citrix.com, sstabellini@kernel.org, qemu-devel@nongnu.org, Jan Beulich , xen-devel@lists.xen.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: Jan Beulich Commit f9e98e5d7a ("xen/blkif: Avoid double access to src->nr_segments") didn't go far enough: src->operation is also being used twice. And nothing was done to prevent the compiler from using the source side of the copy done by blk_get_request() (granted that's very unlikely). Move the barrier()s up, and add another one to blk_get_request(). Note that for completing XSA-155, the barrier() getting added to blk_get_request() would suffice, and hence the changes to xen_blkif.h are more like just cleanup. And since, as said, the unpatched code getting compiled to something vulnerable is very unlikely (and not observed in practice), this isn't being viewed as a new security issue. Signed-off-by: Jan Beulich Reviewed-by: Stefano Stabellini Signed-off-by: Stefano Stabellini --- hw/block/xen_blkif.h | 12 ++++++------ hw/block/xen_disk.c | 2 ++ 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/hw/block/xen_blkif.h b/hw/block/xen_blkif.h index c68487cb..e3b133b 100644 --- a/hw/block/xen_blkif.h +++ b/hw/block/xen_blkif.h @@ -79,14 +79,14 @@ static inline void blkif_get_x86_32_req(blkif_request_t *dst, blkif_x86_32_reque dst->handle = src->handle; dst->id = src->id; dst->sector_number = src->sector_number; - if (src->operation == BLKIF_OP_DISCARD) { + /* Prevent the compiler from using src->... instead. */ + barrier(); + if (dst->operation == BLKIF_OP_DISCARD) { struct blkif_request_discard *s = (void *)src; struct blkif_request_discard *d = (void *)dst; d->nr_sectors = s->nr_sectors; return; } - /* prevent the compiler from optimizing the code and using src->nr_segments instead */ - barrier(); if (n > dst->nr_segments) n = dst->nr_segments; for (i = 0; i < n; i++) @@ -102,14 +102,14 @@ static inline void blkif_get_x86_64_req(blkif_request_t *dst, blkif_x86_64_reque dst->handle = src->handle; dst->id = src->id; dst->sector_number = src->sector_number; - if (src->operation == BLKIF_OP_DISCARD) { + /* Prevent the compiler from using src->... instead. */ + barrier(); + if (dst->operation == BLKIF_OP_DISCARD) { struct blkif_request_discard *s = (void *)src; struct blkif_request_discard *d = (void *)dst; d->nr_sectors = s->nr_sectors; return; } - /* prevent the compiler from optimizing the code and using src->nr_segments instead */ - barrier(); if (n > dst->nr_segments) n = dst->nr_segments; for (i = 0; i < n; i++) diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c index 064c116..cf57814 100644 --- a/hw/block/xen_disk.c +++ b/hw/block/xen_disk.c @@ -679,6 +679,8 @@ static int blk_get_request(struct XenBlkDev *blkdev, struct ioreq *ioreq, RING_I RING_GET_REQUEST(&blkdev->rings.x86_64_part, rc)); break; } + /* Prevent the compiler from accessing the on-ring fields instead. */ + barrier(); return 0; }