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Commit 1f13d75c authored by Roger Pau Monné's avatar Roger Pau Monné Committed by Konrad Rzeszutek Wilk
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xen-blkback: only read request operation from shared ring once 



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.

CC: stable@vger.kernel.org
Signed-off-by: default avatarRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 68a33bfd

drivers/block/xen-blkback/common.h

+4 −4
Original line number Diff line number Diff line
@@ -408,8 +408,8 @@ 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:
@@ -456,8 +456,8 @@ 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: