Bug 1355987 (CVE-2016-6258, xsa182)

Summary: CVE-2016-6258 xsa182 xen: x86: Privilege escalation in PV guests (XSA-182)
Product: [Other] Security Response Reporter: Adam Mariš <amaris>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED WONTFIX QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: dmoppert, security-response-team
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
A vulnerability was found Xen's MMU emulation for x86 PV guests. A malicious administrator of an x86 PV guest could control some of the page table bits, allowing potential control of memory and code execution in the host. x86 HVM and ARM guests could not exploit this flaw.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2016-07-26 13:47:48 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 1360358    
Bug Blocks:    
Attachments:
Description Flags
Xen 4.5 patch
none
Xen 4.6 patch
none
xen-unstable patch none

Description Adam Mariš 2016-07-13 08:32:39 UTC 
ISSUE DESCRIPTION
=================

The PV pagetable code has fast-paths for making updates to pre-existing
pagetable entries, to skip expensive re-validation in safe cases
(e.g. clearing only Access/Dirty bits).  The bits considered safe were too
broad, and not actually safe.

IMPACT
======

A malicous PV guest administrator can escalate their privilege to that
of the host.

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

All versions of Xen are vulnerable.

The vulnerability is only exposed to PV guests on x86 hardware.

The vulnerability is not exposed to x86 HVM guests, or ARM guests.

MITIGATION
==========

Running only HVM guests will avoid this vulnerability.

External References:

http://xenbits.xen.org/xsa/advisory-182.html

Acknowledgements:

Name: the Xen project
Comment 1 Adam Mariš 2016-07-13 08:33:30 UTC 
Created attachment 1179130 [details]
Xen 4.5 patch
Comment 2 Adam Mariš 2016-07-13 08:33:52 UTC 
Created attachment 1179131 [details]
Xen 4.6 patch
Comment 3 Adam Mariš 2016-07-13 08:34:16 UTC 
Created attachment 1179132 [details]
xen-unstable patch
Comment 4 Andrej Nemec 2016-07-21 11:21:46 UTC 
CVE-2016-6258 was assigned to this issue.
Comment 5 Adam Mariš 2016-07-26 13:45:15 UTC 
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1360358]
Comment 8 Fedora Update System 2016-08-05 20:54:38 UTC 
xen-4.6.3-4.fc24 has been pushed to the Fedora 24 stable repository. If problems still persist, please make note of it in this bug report.
Comment 9 Fedora Update System 2016-08-08 23:53:44 UTC 
xen-4.5.3-9.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.