Bug 1486710 - (CVE-2017-14319, xsa234) CVE-2017-14319 xsa234 xen: insufficient grant unmapping checks for x86 PV guests (XSA-234)
CVE-2017-14319 xsa234 xen: insufficient grant unmapping checks for x86 PV gue...
Status: NEW
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
high Severity high
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Assigned To: Red Hat Product Security
impact=important,public=20170912,repo...
: Security
Depends On: 1490884
Blocks:
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Reported: 2017-08-30 07:56 EDT by Adam Mariš
Modified: 2017-09-12 08:24 EDT (History)
13 users (show)

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Description Adam Mariš 2017-08-30 07:56:00 EDT
ISSUE DESCRIPTION
=================

When removing or replacing a grant mapping, the x86 PV specific path
needs to make sure page table entries remain in sync with other
accounting done.  Although the identity of the page frame was
validated correctly, neither the presence of the mapping nor page
writability were taken into account.

IMPACT
======

A malicious or buggy x86 PV guest could escalate its privileges or
crash the hypervisor.

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

All Xen versions are affected.

Only x86 PV guests can leverage the vulnerability.  x86 HVM guests as
well as ARM guests cannot leverage the vulnerability.

MITIGATION
==========

Running only HVM guests will avoid this vulnerability.  However, the
vulnerability is exposed to PV stub qemu serving as the device model
for HVM guests.  Our default assumption is that an HVM guest has
compromised its PV stub qemu.  By extension, it is likely that the
vulnerability is exposed to HVM guests which are served by a PV stub
qemu.

For PV guests, the vulnerability can be avoided if the guest kernel is
controlled by the host rather than guest administrator, provided that
further steps are taken to prevent the guest administrator from loading
code into the kernel (e.g. by disabling loadable modules etc) or from
using other mechanisms which allow them to run code at kernel privilege.

External References:

http://xenbits.xen.org/xsa/advisory-234.html
Comment 1 Adam Mariš 2017-09-12 08:21:35 EDT
Acknowledgments:

Name: Andrew Cooper (Citrix)
Comment 2 Adam Mariš 2017-09-12 08:24:05 EDT
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1490884]

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