[kernel-xen] Xen Security Advisory 116 (CVE-2015-0361) - xen crash due to use after free on hvm guest teardown

[Steven Haigh]

            Xen Security Advisory CVE-2015-0361 / XSA-116
                              version 3

        xen crash due to use after free on hvm guest teardown

UPDATES IN VERSION 3
====================

Public release.

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

Certain data accessible (via hypercalls) by the domain controlling the
execution of a HVM domain is being freed prematurely, leading to the
respective memory regions to possibly be read from and written to in
ways unexpected by their new owner(s).

IMPACT
======

Malicious or buggy stub domain kernels or tool stacks otherwise living
outside of Domain0 can mount a denial of service attack which, if
successful, can affect the whole system.

Only domains controlling HVM guests can exploit this vulnerability.
(This includes domains providing hardware emulation services to HVM
guests.)

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

Xen versions from 4.2 onwards are vulnerable on x86 systems.
ARM systems are not vulnerable.

This vulnerability is only applicable to Xen systems using stub domains
or other forms of disaggregation of control domains for HVM guests.

MITIGATION
==========

Running only PV guests will avoid this issue.

(The security of a Xen system using stub domains is still better than
with a qemu-dm running as an unrestricted dom0 process.  Therefore
users with these configurations should not switch to an unrestricted
dom0 qemu-dm.)

CREDITS
=======

The issue was discovered by Mihai Donțu from Bitdefender who also
supplied the fix.

RESOLUTION
==========

Fixed in:
xen-4.2: Tue Jan 06 2015 Steven Haigh <netwiz at crc.id.au> - 4.2.5-9
- XSA-116 (CVE-2015-0361) xen crash due to use after free on hvm guest
teardown

xen44-4.4: Tue Jan 06 2015 Steven Haigh <netwiz at crc.id.au> - 4.4.1-9
- XSA-116 (CVE-2015-0361) xen crash due to use after free on hvm guest
teardown

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