diff options
| author | Stefano Stabellini <stefano.stabellini@eu.citrix.com> | 2015-12-18 15:10:09 +0000 |
|---|---|---|
| committer | Michael Roth <mdroth@linux.vnet.ibm.com> | 2016-03-15 12:20:35 -0500 |
| commit | ff083d3c3bc3e3e0194a8d1bd0419121edc054fc (patch) | |
| tree | 57d3d22e73d1bf5f3df52c3bb9e034528f240776 /hw | |
| parent | 4d59e78dfe6c1df181b54ee90f273de7d4cdfe86 (diff) | |
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>
Diffstat (limited to 'hw')
| -rw-r--r-- | hw/display/xenfb.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c index 5e324ef62d..4e2a27a3d6 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; |