|From the Red Hat bugzilla:
CVE-2013-0151: nested virtualization on 32-bit exposes host crash
When performing nested virtualisation Xen would incorrectly map guest
pages for extended periods using an interface which is only intended
for transient mappings. In some configurations there are a limited
number of slots available for these transient mappings and exhausting
them leads to a host crash and therefore a Denial of Service attack.
A malicious guest administrator can, by enabling nested virtualisation
from within the guest, trigger the issue.
CVE-2013-0152: nested HVM exposes host to being driven out of memory by guest
Guests are currently permitted to enable nested virtualization on
themselves. Missing error handling cleanup in the handling code makes
it possible for a guest, particularly a multi-vCPU one, to repeatedly
invoke this operation, thus causing a leak of - over time - unbounded
amounts of memory.
A malicious domain can mount a denial of service attack affecting the