virtunoid -- a guest -> host breakout for qemu-kvm
Nelson Elhage <nelhage@nelhage.com>
@nelhage
http://blog.nelhage.com/

This is an exploit for CVE-2011-1751, a missing check in the qemu-kvm
userspace driver for the KVM Linux Kernel-mode Virtual Machine. For
more information, see the slides from my talk at BlackHat/DEFCON 2011:
<http://nelhage.com/talks/kvm-defcon-2011.pdf>

RUNNING THE EXPLOIT
-------------------

The exploit expects to be run as root inside a guest. For maximum
reliability, the provided Makefile builds an initrd containing the
exploit that can be used to run the exploit in as minimal an
environment as possible. While I have seen the exploit work inside a
fully booted Linux guest, there is a high chance of just crashing the
host.

The provided linux-3.0.0-config Linux config file contains the config
I used for my demo at DEFCON. The details of the config aren't too
important, except that it needs to contain an appropriate driver for
the virtual network card; I've just provided mine for
convenience. I've also posted a suitable bzImage at
<https://nelhage.com/files/bzImage-kvm-demo>.

To run the exploit, build an appopriate kernel or download mine, and
run

  kvm -kernel bzImage -initrd initrd.gz

virtunoid-config.h contains various addresses needed for the
exploit. The provided version is targeted at Ubuntu's
qemu-kvm_0.14.0+noroms-0ubuntu4_amd6, which can be downloaded from
<https://launchpad.net/ubuntu/+source/qemu-kvm/0.14.0+noroms-0ubuntu4/+build/2385343/+files/qemu-kvm_0.14.0%2Bnoroms-0ubuntu4_amd64.deb>

For any other version, the addresses and some of the offsets in
virtunoid-config.h will need to be tweaked.

KNOWN ISSUES
------------

Most of these could be fixed, but I didn't feel particularly inclined
for a proof-of-concept exploit. If you do feel like fixing one or
more, let me know.

* This exploit requires "-net user" with the default settings (or no
  -net options at all, which defaults to "-net nic -net user"). This
  requirement could be fixed, but this is a proof-of-concept.

* This exploit only works on the specific Ubuntu qemu-kvm build it is
  built for. This exploit uses symbols that don't exist prior to
  qemu-kvm 0.13.51.

* This exploit is still somewhat unreliable. I observe a failure rate
  of maybe 1 in 20 running it from an initrd on my test rig. There are
  a few different failure modes, the most common being SEGVing
  qemu-kvm instead of successful exploitation.

* The guest locks up after the exploit.

LEGALESE
--------

Copyright (c) Nelson Elhage.
All rights reserved.

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