Commit 8a4577e6 authored by Roger Pau Monné's avatar Roger Pau Monné Committed by Luis Henriques

xen-blkback: only read request operation from shared ring once

commit 1f13d75c 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: 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>
[ luis: backported to 3.16:
  - replaced READ_ONCE() by ACCESS_ONCE() ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 2419fe7e
......@@ -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:
......
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