[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [qemu-xen stable-4.2] xenfb: avoid reading twice the same fields from the shared page
commit 5081fc1c773d2a83ec7a867f030323b8b6956cd1 Author: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> AuthorDate: Fri Dec 18 15:45:14 2015 +0000 Commit: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> CommitDate: Fri Dec 18 16:00:38 2015 +0000 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@xxxxxxxxxxxxx> --- hw/xenfb.c | 10 ++++++---- 1 files changed, 6 insertions(+), 4 deletions(-) diff --git a/hw/xenfb.c b/hw/xenfb.c index 338800a..9cf603a 100644 --- a/hw/xenfb.c +++ b/hw/xenfb.c @@ -798,18 +798,20 @@ 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; -- generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.2 _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxx http://lists.xensource.com/xen-changelog
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