XSA-108 Xen security update has been released. This update includes a security fix for a vulnerability affecting Xen hypervisors version 4.1.x and onward. We highly recommend updating your hypervisor servers as soon as possible.
This issue affects RHEL/CentOS 6.x static Xen hypervisors version Xen 4.1 and higher, running HVM guests. In OnApp, RHEL/CentOS 6.x with Xen 4.2.x hypervisors running Windows and FreeBSD guests are vulnerable.
The MSR range specified for APIC use in the x2APIC access model spans 256 MSRs. Hypervisor code emulating read and write access to these MSRs erroneously covered 1024 MSRs.
While the write emulation path is written such that access to the extra MSRs would not have any bad effect (they end up being no-ops), the read path would (attempt to) access memory beyond the single page set up for APIC emulation.
A buggy or malicious HVM guest can crash the host, or read data relating to other guests or the hypervisor itself.
- Xen 4.1 and onward are vulnerable.
- Only x86 systems are vulnerable.
- ARM systems are not affected.
Running only PV guests will avoid this vulnerability.
Upgrade and reboot your RHEL/CentOS 6.x static Xen hypervisors as soon as possible to resolve this issue.
For full upgrade, process with regular steps from the Static Hypervisor upgrade documentation. Full upgrade is highly recommended to make sure your update to the latest Xen kernel and hypervisor tools:
In case you want to perform a quick update, run:
# yum update xen
# yum update xen xen-hypervisor
Reboot your hypervisor after the upgrade!
To guarantee uptime of your virtual servers, live migrate them to another hypervisor before an upgrade and live migrate them back after the upgrade is complete.