44 lines
1.4 KiB
Diff
44 lines
1.4 KiB
Diff
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References: bsc#957988
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xenfb: avoid reading twice the same fields from the shared page
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Reading twice the same field could give the guest an attack of
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opportunity. In the case of event->type, gcc could compile the switch
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statement into a jump table, effectively ending up reading the type
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field multiple times.
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This is part of XSA-155.
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Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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Index: xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/display/xenfb.c
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===================================================================
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--- xen-4.6.0-testing.orig/tools/qemu-xen-dir-remote/hw/display/xenfb.c
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+++ xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/display/xenfb.c
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@@ -779,18 +779,20 @@ static void xenfb_invalidate(void *opaqu
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static void xenfb_handle_events(struct XenFB *xenfb)
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{
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- uint32_t prod, cons;
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+ uint32_t prod, cons, out_cons;
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struct xenfb_page *page = xenfb->c.page;
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prod = page->out_prod;
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- if (prod == page->out_cons)
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+ out_cons = page->out_cons;
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+ if (prod == out_cons)
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return;
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xen_rmb(); /* ensure we see ring contents up to prod */
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- for (cons = page->out_cons; cons != prod; cons++) {
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+ for (cons = out_cons; cons != prod; cons++) {
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union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons);
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+ uint8_t type = event->type;
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int x, y, w, h;
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- switch (event->type) {
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+ switch (type) {
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case XENFB_TYPE_UPDATE:
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if (xenfb->up_count == UP_QUEUE)
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xenfb->up_fullscreen = 1;
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