Xen.org security team
2013-Oct-10 12:22 UTC
Xen Security Advisory 67 (CVE-2013-4368) - Information leak through outs instruction emulation
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Xen Security Advisory CVE-2013-4368 / XSA-67
version 2
Information leak through outs instruction emulation
UPDATES IN VERSION 2
===================
Public release.
ISSUE DESCRIPTION
================
The emulation of the outs instruction for 64-bit PV guests uses an
uninitialized variable as the segment base for the source data if an FS: or
GS: segment override is used, and if the segment descriptor the respective
non-null selector in the corresponding selector register points to cannot be
read by the emulation code (this is possible if the segment register was
loaded before a more recent GDT or LDT update, i.e. the segment register
contains stale data).
A malicious guest might be able to get hold of contents of the hypervisor
stack, through the fault address passed to the page fault handler if the outs
raises such a fault (which is mostly under guest control). Other methods for
indirectly deducing information also exist.
IMPACT
=====
A malicious 64-bit PV guest might conceivably gain access to sensitive data
relating to other guests.
VULNERABLE SYSTEMS
=================
Xen 3.1.x and later are vulnerable.
Only 64-bit PV guests can take advantage of this vulnerability.
MITIGATION
=========
Running only HVM or 32-bit PV guests will avoid this issue.
CREDITS
======
This issue was discovered by Coverity Scan and Matthew Daley.
RESOLUTION
=========
Applying the attached patch resolves this issue.
xsa67.patch Xen 4.2.x, Xen 4.3.x, xen-unstable
$ sha256sum xsa67*.patch
7de3ac9baa6cd9fead46e68912dfa0189e900095317645d0e33d85346fc8a028 xsa67.patch
$
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