xen-kernel -- Information leak through version information hypercall

The Xen Project reports:

The code handling certain sub-operations of the
HYPERVISOR_xen_version hypercall fails to fully initialize all
fields of structures subsequently copied back to guest memory. Due
to this hypervisor stack contents are copied into the destination of
the operation, thus becoming visible to the guest.
A malicious guest might be able to read sensitive data relating to
other guests.