xen - security update

Multiple vulnerabilities have been discovered in the Xen hypervisor. The
Common Vulnerabilities and Exposures project identifies the following
problems:

• CVE-2016-7092 (XSA-185)

Jeremie Boutoille of Quarkslab and Shangcong Luan of Alibaba
discovered a flaw in the handling of L3 pagetable entries, allowing
a malicious 32-bit PV guest administrator can escalate their
privilege to that of the host.

• CVE-2016-7094 (XSA-187)

x86 HVM guests running with shadow paging use a subset of the x86
emulator to handle the guest writing to its own pagetables. Andrew
Cooper of Citrix discovered that there are situations a guest can
provoke which result in exceeding the space allocated for internal
state. A malicious HVM guest administrator can cause Xen to fail a
bug check, causing a denial of service to the host.

For Debian 7 Wheezy, these problems have been fixed in version
4.1.6.lts1-2. For Debian 8 Jessie, these problems have been fixed in
version 4.4.1-9+deb8u7.

We recommend that you upgrade your xen packages.

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: <https://wiki.debian.org/LTS&gt;