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Groups > linux.kernel > #1310649
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|---|---|
| From | Kamal Mostafa <kamal@canonical.com> |
| Newsgroups | linux.kernel |
| Subject | [PATCH 4.2.y-ckt 235/305] xen-blkback: only read request operation from shared ring once |
| Date | Sat, 16 Jan 2016 01:30:04 +0100 |
| Message-ID | <qRmUI-5ah-77@gated-at.bofh.it> (permalink) |
| References | <qRmBj-507-3@gated-at.bofh.it> |
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| Approved | robomod@news.nic.it |
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| X-Original-Cc | Roger Pau Monné <roger.pau@citrix.com>, David Vrabel <david.vrabel@citrix.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Kamal Mostafa <kamal@canonical.com> |
| X-Original-Date | Fri, 15 Jan 2016 16:00:49 -0800 |
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| Xref | csiph.com linux.kernel:1310649 |
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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?= <roger.pau@citrix.com>
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@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Kamal Mostafa <kamal@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 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
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[PATCH 4.2.y-ckt 235/305] xen-blkback: only read request operation from shared ring once Kamal Mostafa <kamal@canonical.com> - 2016-01-16 01:30 +0100
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