From: Roger Pau Monné Date: Tue, 3 Nov 2015 16:34:09 +0000 (+0000) Subject: xen-blkback: only read request operation from shared ring once X-Git-Tag: v3.16.35~744 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8a4577e63e31c1296fd8ee4016345f0be8284c47;p=thirdparty%2Fkernel%2Fstable.git xen-blkback: only read request operation from shared ring once 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 [ luis: backported to 3.16: - replaced READ_ONCE() by ACCESS_ONCE() ] Signed-off-by: Luis Henriques --- diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index f65b807e32361..ef64f59921a7c 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 = ACCESS_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 = ACCESS_ONCE(src->operation); + switch (dst->operation) { case BLKIF_OP_READ: case BLKIF_OP_WRITE: case BLKIF_OP_WRITE_BARRIER: