File xsa155-qemuu-xenfb.patch of Package xen

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File xsa155-qemuu-xenfb.patch of Package xen (Revision 0056964abc120d4d6c2d28b4b3950a02)

Currently displaying revision 0056964abc120d4d6c2d28b4b3950a02 , Show latest

References: bsc#957988

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>

Index: xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/display/xenfb.c
===================================================================
--- xen-4.6.0-testing.orig/tools/qemu-xen-dir-remote/hw/display/xenfb.c
+++ xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/display/xenfb.c
@@ -779,18 +779,20 @@ static void xenfb_invalidate(void *opaqu
 
 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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File xsa155-qemuu-xenfb.patch of Package xen (Revision 0056964abc120d4d6c2d28b4b3950a02)

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