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.
A malicious 64-bit PV guest might conceivably gain access to sensitive data
relating to other guests.
Red Hat would like to thank the Xen project for reporting this issue.
Created xen tracking bugs for this issue:
Affects: fedora-all [bug 1017843]
This issue has been addressed in following products:
Red Hat Enterprise Linux 5
Via RHSA-2013:1449 https://rhn.redhat.com/errata/RHSA-2013-1449.html
xen-4.2.3-4.fc18 has been pushed to the Fedora 18 stable repository. If problems still persist, please make note of it in this bug report.
xen-4.2.3-4.fc19 has been pushed to the Fedora 19 stable repository. If problems still persist, please make note of it in this bug report.