Xen Security Advisory 482 v2 - Linux privcmd driver can circumvent kernel lockdown

[Xen.org security team <security@xxxxxxx>]

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                    Xen Security Advisory XSA-482
                              version 2

          Linux privcmd driver can circumvent kernel lockdown

UPDATES IN VERSION 2
====================

Public release.

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

The Linux kernel's privcmd driver can be abused to circumvent kernel
lockdown (secure boot), e.g. by modifying page tables to enable user
mode to modify kernel memory.

The CNA covering Linux has refused to assign a CVE at this juncture.

IMPACT
======

An administrator of an unprivileged guest booted in secure mode is able
to perform actions on the kernel which should not be possible in secure
mode.

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

PV, PVH and HVM guests running Linux using secure boot are vulnerable.

BSD based systems are believed not to be vulnerable due to a lack of
secure boot support.

MITIGATION
==========

There is no known mitigation.

CREDITS
=======

This issue was discovered by Teddy Astie of Vates.

RESOLUTION
==========

Applying the set of attached patches resolves this issue.

xsa482-linux-?.patch           Linux

$ sha256sum xsa482*
a4e67d2c773e2e13252337e4b64c08b342c0eb2e0e92271a79dc588ac34e7c3a  
xsa482-linux-1.patch
dd952c1fc49ceb47803b78e15cfe3f7f11a845b29c6b2a80afa7a9eaa60a00ec  
xsa482-linux-2.patch
$

DEPLOYMENT DURING EMBARGO
=========================

Deployment of patches or mitigations is NOT permitted (except where
all the affected systems and VMs are administered and used only by
organisations which are members of the Xen Project Security Issues
Predisclosure List).  Specifically, deployment on public cloud systems
is NOT permitted.

This is because the patches need to be applied to the guests.

Deployment is permitted only AFTER the embargo ends.

(Note: this during-embargo deployment notice is retained in
post-embargo publicly released Xen Project advisories, even though it
is then no longer applicable.  This is to enable the community to have
oversight of the Xen Project Security Team's decisionmaking.)

For more information about permissible uses of embargoed information,
consult the Xen Project community's agreed Security Policy:
  http://www.xenproject.org/security-policy.html
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Attachment: xsa482-linux-1.patch
Description: Binary data

Attachment: xsa482-linux-2.patch
Description: Binary data