From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753927AbcARDY4 (ORCPT ); Sun, 17 Jan 2016 22:24:56 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:59412 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753138AbcARDWF (ORCPT ); Sun, 17 Jan 2016 22:22:05 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Konrad Rzeszutek Wilk" , "David Vrabel" , "=?UTF-8?q?Roger=20Pau=20Monn=C3=A9?=" Date: Mon, 18 Jan 2016 03:18:35 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 23/70] xen-blkback: only read request operation from shared ring once In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.247 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.76-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Roger Pau Monné commit 1f13d75ccb806260079e0679d55d9253e370ec8a upstream. A compiler may load a switch statement value multiple times, which could be bad when the value is in memory shared with the frontend. When converting a non-native request to a native one, ensure that src->operation is only loaded once by using READ_ONCE(). This is part of XSA155. Signed-off-by: Roger Pau Monné Signed-off-by: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk [bwh: Backported to 3.2: - s/READ_ONCE/ACCESS_ONCE/ - Adjust context] Signed-off-by: Ben Hutchings --- drivers/block/xen-blkback/common.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -238,11 +238,11 @@ static inline void blkif_get_x86_32_req( struct blkif_x86_32_request *src) { int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST; - dst->operation = src->operation; + dst->operation = ACCESS_ONCE(src->operation); dst->nr_segments = src->nr_segments; dst->handle = src->handle; dst->id = src->id; - switch (src->operation) { + switch (dst->operation) { case BLKIF_OP_READ: case BLKIF_OP_WRITE: case BLKIF_OP_WRITE_BARRIER: @@ -267,11 +267,11 @@ static inline void blkif_get_x86_64_req( struct blkif_x86_64_request *src) { int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST; - dst->operation = src->operation; + dst->operation = ACCESS_ONCE(src->operation); dst->nr_segments = src->nr_segments; dst->handle = src->handle; dst->id = src->id; - switch (src->operation) { + switch (dst->operation) { case BLKIF_OP_READ: case BLKIF_OP_WRITE: case BLKIF_OP_WRITE_BARRIER: