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            Xen Security Advisory CVE-2023-34320 / XSA-436

           arm: Guests can trigger a deadlock on Cortex-A77

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

Cortex-A77 cores (r0p0 and r1p0) are affected by erratum 1508412
where software, under certain circumstances, could deadlock a core
due to the execution of either a load to device or non-cacheable memory,
and either a store exclusive or register read of the Physical
Address Register (PAR_EL1) in close proximity.

IMPACT
======

A (malicious) guest that doesn't include the workaround for erratum
1508412 could deadlock the core.  This will ultimately result to
a deadlock of the system.

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

Systems running all version of Xen are affected.

This bug is specific to Arm Cortex-A77 cores r0p0 and r1p0.

MITIGATION
==========

There are no known mitigations.

NOTE REGARDING LACK OF EMBARGO
==============================

This issue has been publicly documented.

RESOLUTION
==========

To handle properly the erratum, it is necessary to have an updated
firmware and that both the hypervisor and guest OSes have the workaround.
This means it is not possible to security support Xen on the Cortex-A77,
even on systems which have the workaround enabled.

Applying the attached patches will document the situation and also
add the workaround in Xen if someone wish to run on Cortex-A77 with
only trusted guests.

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.

xsa436/xsa436.patch           xen-unstable - Xen 4.17.x
xsa436/xsa436-4.16.patch      Xen 4.16.x
xsa436/xsa436-4.15.patch      Xen 4.15.x

$ sha256sum xsa436* xsa436*/*
64d34753cdbbcfec2c80db2daad98529bf900935419d0214057e962098b38160  xsa436.meta
cc0f1303d4ad4c4750bd555622b87a9721e0253759b07915e6ba5216c24e8f8d  xsa436/xsa436.patch
97d1bd7716637efce1fa5d7f608d7f26b2b396fa20b966c8c0cd22ef61dc07d4  xsa436/xsa436-4.15.patch
e1264a44df39d56a2c6246d8f9f511d0371a5f416c364ef766ea5a59e7b46f92  xsa436/xsa436-4.16.patch
$
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