blob: dfc871375b6db50241762fd948fb71291f285ed4 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
|
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>
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;
|
