Xen Security Advisory 404 v1 (CVE-2022-21123,CVE-2022-21124,CVE-2022-21166) - x86: MMIO Stale Data vulnerabilities

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

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 Xen Security Advisory CVE-2022-21123,CVE-2022-21124,CVE-2022-21166 / XSA-404

                 x86: MMIO Stale Data vulnerabilities

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

This issue is related to the SRBDS, TAA and MDS vulnerabilities.  Please
see:

  https://xenbits.xen.org/xsa/advisory-320.html (SRBDS)
  https://xenbits.xen.org/xsa/advisory-305.html (TAA)
  https://xenbits.xen.org/xsa/advisory-297.html (MDS)

Please see Intel's whitepaper:

  
https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/processor-mmio-stale-data-vulnerabilities.html

IMPACT
======

An attacker might be able to directly read or infer data from other
security contexts in the system.  This can include data belonging to
other VMs, or to Xen itself.  The degree to which an attacker can obtain
data depends on the CPU, and the system configuration.

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

Systems running all versions of Xen are affected.

Only x86 processors are vulnerable.  Processors from other manufacturers
(e.g. ARM) are not believed to be vulnerable.

Only Intel based processors are affected.  Processors from other x86
manufacturers (e.g. AMD) are not believed to be vulnerable.

Please consult the Intel Security Advisory for details on the affected
processors and configurations.

Per Xen's support statement, PCI passthrough should be to trusted
domains because the overall system security depends on factors outside
of Xen's control.

As such, Xen, in a supported configuration, is not vulnerable to
DRPW/SBDR.

MITIGATION
==========

All mitigations depend on functionality added in the IPU 2022.1 (May
2022) microcode release from Intel.  Consult your dom0 OS vendor.

To the best of the security team's understanding, the summary is as
follows:

Server CPUs (Xeon EP/EX, Scalable, and some Atom servers), excluding
Xeon E3 (which use the client CPU design), are potentially vulnerable to
DRPW (CVE-2022-21166).

Client CPUs (inc Xeon E3) are, furthermore, potentially vulnerable to
SBDR (CVE-2022-21123) and SBDS (CVE-2022-21125).

SBDS only affects CPUs vulnerable to MDS.  On these CPUs, there are
previously undiscovered leakage channels.  There is no change to the
existing MDS mitigations.

DRPW and SBDR only affects configurations where less privileged domains
have MMIO mappings of buggy endpoints.  Consult your hardware vendor.

In configurations where less privileged domains have MMIO access to
buggy endpoints, `spec-ctrl=unpriv-mmio` can be enabled which will cause
Xen to mitigate cross-domain fill buffer leakage, and extend SRBDS
protections to protect RNG data from leakage.

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.

The patches are still under review.  An update will be sent once they
are reviewed and the backports are done.

xsa404/xsa404-?.patch           xen-unstable

$ sha256sum xsa404*/*
18b307c2cbbd08d568e9dcb2447901d94e22ff1e3945c3436173aa693f6456fb  
xsa404/xsa404-1.patch
d6f193ad963396285e983aa1c18539f67222582711fc62105c21b71b3b53a97d  
xsa404/xsa404-2.patch
d2c123ccdf5eb9f862d6e9cb0e59045ae18799a07db149c7d90e301ca20436aa  
xsa404/xsa404-3.patch
$

NOTE CONCERNING CVE-2022-21127 / Update to SRBDS
================================================

An issue was discovered with the SRBDS microcode mitigation.  A
microcode update was released as part of Intel's IPU 2022.1 in May 2022.

Updating microcode is sufficient to fix the issue, with no extra actions
required on Xen's behalf.  Consult your dom0 OS vendor or OEM for
updated microcode.

NOTE CONCERNING CVE-2022-21180 / Undefined MMIO Hang
====================================================

A related issue was discovered.  See:

  
https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/undefined-mmio-hang.html

Xen is not vulnerable to UMH in supported configurations.

The only mitigation to is avoid passing impacted devices through to
untrusted guests.
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Attachment: xsa404/xsa404-1.patch
Description: Binary data

Attachment: xsa404/xsa404-2.patch
Description: Binary data

Attachment: xsa404/xsa404-3.patch
Description: Binary data