ISSUE DESCRIPTION
=================

Along with their main kernel binary, unprivileged guests may arrange
to have their Xen environment load (kernel) symbol tables for their
use.  The ELF image metadata created for this purpose has a few unused
bytes when the symbol table binary is in 32-bit ELF format.  These
unused bytes were not properly cleared during symbol table loading.

IMPACT
======

A malicious unprivileged guest may be able to obtain sensitive
information from the host.

The information leak is small and not under the control of the guest,
so effectively exploiting this vulnerability is probably difficult.

VULNERABLE SYSTEMS
==================

Only Xen version 4.7 is affected.  Xen versions 4.6 and earlier are not
affected.

The vulnerability is not exposed to x86 HVM guests, unless the host
toolstack has configured to load the guest with a non-default loader,
rather than hvmloader.

MITIGATION
==========

There is no known mitigation.

External References:

http://xenbits.xen.org/xsa/advisory-194.html

Acknowledgements:

Name: the Xen project
Upstream: Roger Pau Monné (Citrix)