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 Xen Security Advisory CVE-2025-27466,CVE-2025-58142,CVE-2025-58143 / XSA-472
                                   version 2

           Mutiple vulnerabilities in the Viridian interface

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

Public release.

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

There are multiple issues related to the handling and accessing of guest
memory pages in the viridian code:

 1. A NULL pointer dereference in the updating of the reference TSC area.
    This is CVE-2025-27466.

 2. A NULL pointer dereference by assuming the SIM page is mapped when
    a synthetic timer message has to be delivered.  This is
    CVE-2025-58142.

 3. A race in the mapping of the reference TSC page, where a guest can
    get Xen to free a page while still present in the guest physical to
    machine (p2m) page tables.  This is CVE-2025-58143.

IMPACT
======

Denial of Service (DoS) affecting the entire host, information leaks, or
elevation of privilege.

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

Xen versions 4.13 and newer are vulnerable.  Xen versions 4.12 and older
are not vulnerable.

Only x86 HVM guests which have the reference_tsc or stimer viridian
extensions enabled are vulnerable.

MITIGATION
==========

Not enabling the reference_tsc and stimer viridian extensions will avoid
the issues.

CREDITS
=======

This issue was discovered by Roger Pau Monné of XenServer.

RESOLUTION
==========

Applying the appropriate set of attached patches 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.

xsa472-?.patch         xen-unstable - Xen 4.17.x

$ sha256sum xsa472*
16e14b3cc87800c08d96adc18e66aa4a20a77834af12b9cdd01d739882f07b7d  xsa472-1.patch
4be6a1066fbec367e8c9883240cec2a78671d484928d51ac5fb82e2c539e38ca  xsa472-2.patch
9e1972a2b5a7a817b25cad0fa80c983198bb73a2788a4d0b5cdcaca4518a57cf  xsa472-3.patch
$

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

Deployment of the patches (but not 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.

This is because the mitigations are guest visible changes, and hence could
give hints to users about the upcoming vulnerabilities.

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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