[3.19.y-ckt stable] Patch "xen-blkback: only read request operation from shared ring once" has been added to the 3.19.y-ckt tree
Kamal Mostafa
kamal at canonical.com
Wed Jan 20 01:03:53 UTC 2016
This is a note to let you know that I have just added a patch titled
xen-blkback: only read request operation from shared ring once
to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue
This patch is scheduled to be released in version 3.19.8-ckt13.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From 19e8d93166865e7eb40c7214b5c5551b4dea23cc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= <roger.pau at citrix.com>
Date: Tue, 3 Nov 2015 16:34:09 +0000
Subject: xen-blkback: only read request operation from shared ring once
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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 <roger.pau at citrix.com>
Signed-off-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
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 f65b807..d179195 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -391,8 +391,8 @@ 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:
@@ -439,8 +439,8 @@ 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
More information about the kernel-team
mailing list