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authorStefano Stabellini <stefano.stabellini@eu.citrix.com>2015-12-18 15:10:09 +0000
committerMichael Roth <mdroth@linux.vnet.ibm.com>2016-03-15 12:20:35 -0500
commitff083d3c3bc3e3e0194a8d1bd0419121edc054fc (patch)
tree57d3d22e73d1bf5f3df52c3bb9e034528f240776
parent4d59e78dfe6c1df181b54ee90f273de7d4cdfe86 (diff)
downloadhqemu-ff083d3c3bc3e3e0194a8d1bd0419121edc054fc.zip
hqemu-ff083d3c3bc3e3e0194a8d1bd0419121edc054fc.tar.gz
xenfb: avoid reading twice the same fields from the shared page
Reading twice the same field could give the guest an attack of opportunity. In the case of event->type, gcc could compile the switch statement into a jump table, effectively ending up reading the type field multiple times. This is part of XSA-155. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> (cherry picked from commit 7ea11bf376aea4bf8340eb363de9777c7f93e556) Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
-rw-r--r--hw/display/xenfb.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index 5e324ef..4e2a27a 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -784,18 +784,20 @@ static void xenfb_invalidate(void *opaque)
static void xenfb_handle_events(struct XenFB *xenfb)
{
- uint32_t prod, cons;
+ uint32_t prod, cons, out_cons;
struct xenfb_page *page = xenfb->c.page;
prod = page->out_prod;
- if (prod == page->out_cons)
+ out_cons = page->out_cons;
+ if (prod == out_cons)
return;
xen_rmb(); /* ensure we see ring contents up to prod */
- for (cons = page->out_cons; cons != prod; cons++) {
+ for (cons = out_cons; cons != prod; cons++) {
union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons);
+ uint8_t type = event->type;
int x, y, w, h;
- switch (event->type) {
+ switch (type) {
case XENFB_TYPE_UPDATE:
if (xenfb->up_count == UP_QUEUE)
xenfb->up_fullscreen = 1;
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