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Advisory

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            Xen Security Advisory CVE-2022-33744 / XSA-406
                               version 3

             Arm guests can cause Dom0 DoS via PV devices

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

Public release.

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

When mapping pages of guests on Arm, dom0 is using an rbtree to keep
track of the foreign mappings.

Updating of that rbtree is not always done completely with the related
lock held, resulting in a small race window, which can be used by
unprivileged guests via PV devices to cause inconsistencies of the
rbtree. These inconsistencies can lead to Denial of Service (DoS) of
dom0, e.g. by causing crashes or the inability to perform further
mappings of other guests' memory pages.

IMPACT
======

A guest performing multiple I/Os of PV devices in parallel can cause
DoS of dom0 and thus of the complete host.

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

Only Arm systems (32-bit and 64-bit) are vulnerable. Dom0 Linux versions
3.13 - 5.18 are vulnerable.

X86 systems are not vulnerable.

MITIGATION
==========

There is no mitigation available.

CREDITS
=======

This issue was discovered by Oleksandr Tyshchenko of EPAM.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

Note that patches for released versions are generally prepared to
apply to the stable branches, and may not apply cleanly to the most
recent release tarball.  Downstreams are encouraged to update to the
tip of the stable branch before applying these patches.

xsa406-linux.patch     Linux 3.13 - 5.19-rc

$ sha256sum xsa406*
7a789f564b3365cade6e95d549dbbd5a8b7b5e53d09bc5a463c77dfefd5a4182  xsa406-linux.patch
$

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

Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
administrators.

But: Distribution of updated software is prohibited (except to other
members of the predisclosure list).

Predisclosure list members who wish to deploy significantly different
patches and/or mitigations, please contact the Xen Project Security
Team.


(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is then no longer applicable.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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