From: Andriy Gapon <avg@FreeBSD.org>
Date: Thu, 22 Dec 2011 09:34:30 +0000 (+0200)
Subject: usb-ohci: td.cbp incorrectly updated near page end
X-Git-Tag: qemu-xen-4.3.0-rc1~18^2~48
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=23201c64a789cf948fedcea221a4b6e197fcd628;p=qemu-upstream-4.3-testing.git

usb-ohci: td.cbp incorrectly updated near page end

The current code that updates the cbp value after a transfer looks like this:
td.cbp += ret;
if ((td.cbp & 0xfff) + ret > 0xfff) {
	<handle page overflow>
because the 'ret' value is effectively added twice the check may fire too early
when the overflow hasn't happened yet.

Below is one of the possible changes that correct the behavior:

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---

diff --git a/hw/usb-ohci.c b/hw/usb-ohci.c
index c2981c59a..c27014a88 100644
--- a/hw/usb-ohci.c
+++ b/hw/usb-ohci.c
@@ -1025,10 +1025,10 @@ static int ohci_service_td(OHCIState *ohci, struct ohci_ed *ed)
         if (ret == len) {
             td.cbp = 0;
         } else {
-            td.cbp += ret;
             if ((td.cbp & 0xfff) + ret > 0xfff) {
-                td.cbp &= 0xfff;
-                td.cbp |= td.be & ~0xfff;
+                td.cbp = (td.be & ~0xfff) + ((td.cbp + ret) & 0xfff);
+            } else {
+                td.cbp += ret;
             }
         }
         td.flags |= OHCI_TD_T1;