From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , David Vrabel , Konrad Rzeszutek Wilk , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 235/305] xen-blkback: only read request operation from shared ring once Date: Fri, 15 Jan 2016 16:00:49 -0800 Message-Id: <1452902519-2754-236-git-send-email-kamal@canonical.com> In-Reply-To: <1452902519-2754-1-git-send-email-kamal@canonical.com> References: <1452902519-2754-1-git-send-email-kamal@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.2.8-ckt2 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= 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 Signed-off-by: Kamal Mostafa --- drivers/block/xen-blkback/common.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index 45a044a..619bd60 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -399,8 +399,8 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst, struct blkif_x86_32_request *src) { int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST, j; - dst->operation = src->operation; - switch (src->operation) { + dst->operation = READ_ONCE(src->operation); + switch (dst->operation) { case BLKIF_OP_READ: case BLKIF_OP_WRITE: case BLKIF_OP_WRITE_BARRIER: @@ -447,8 +447,8 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst, struct blkif_x86_64_request *src) { int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST, j; - dst->operation = src->operation; - switch (src->operation) { + dst->operation = READ_ONCE(src->operation); + switch (dst->operation) { case BLKIF_OP_READ: case BLKIF_OP_WRITE: case BLKIF_OP_WRITE_BARRIER: -- 1.9.1