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Advisory

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            Xen Security Advisory CVE-2017-17046 / XSA-245
                               version 3

                 ARM: Some memory not scrubbed at boot

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

Normalize version tags

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

This bug was discussed publicly before it was realised that it was a
security vulnerability.

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

Data can remain readable in DRAM across soft and even hard reboots.
To ensure that sensitive data is not leaked from one domain to another
after a reboot, Xen must "scrub" all memory on boot (write it with
zeroes).

Unfortunately, it was discovered that when memory was in disjoint blocks,
or when the first block didn't begin at physical address 0, arithmetic
errors meant that some memory was not scrubbed.

IMPACT
======

Sensitive information from one domain before a reboot might be visible
to another domain after a reboot.

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

Only ARM systems are vulnerable.

All versions of Xen since 4.5 are vulnerable.

Only hardware with disjoint blocks, or physical addresses not starting at 0
are vulnerable; this includes the majority of ARM systems.

MITIGATION
==========

None.

RESOLUTION
==========

Applying the appropriate attached patches resolves this issue.

xsa245/*.patch         Xen (All versions)

$ sha256sum xsa245* xsa245*/*
121829263b85fcb5eac8e38fb44e77d3aab1dd7ae6ef665bf84bb49e5e161d24  xsa245.meta
526f9e1b127fbb316762ce8e8f4563bc9de0c55a1db581456a3017d570d35bdd  xsa245/0001-xen-page_alloc-Cover-memory-unreserved-after-boot-in.patch
7164010112fcccd9cd88e72ace2eeabdb364dd6f4d05c434686267d18067f420  xsa245/0002-xen-arm-Correctly-report-the-memory-region-in-the-du.patch
$

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