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AUSCERT External Security Bulletin Redistribution
Xen Security Advisory CVE-2014-3125 / XSA-91 version 3
7 May 2014
AusCERT Security Bulletin Summary
Operating System: Xen
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Denial of Service -- Existing Account
CVE Names: CVE-2014-3125
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Xen Security Advisory CVE-2014-3125 / XSA-91
Hardware timer context is not properly context switched on ARM
UPDATES IN VERSION 3
This issue has been assigned CVE-2014-3125.
When running on an ARM platform Xen was not context switching the
CNTKCTL_EL1 register, which is used by the guest kernel to control
access by userspace processes to the hardware timers. This meant that
any guest can reconfigure these settings for the entire system.
A malicious guest kernel can reconfigure CNTKCTL_EL1 to block
userspace access to the timer hardware for all domains, including
control domains. Depending on the other guest kernels in use this may
cause an unexpected exception in those guests which may lead to a
kernel crash and therefore a denial of service.
64-bit ARM Linux is known to be susceptible to crashing in this way.
A malicious guest kernel can also enable userspace access to the timer
control registers, which may not be expected by kernels running in
other domains. This can allow user processes to reprogram timer
interrupts and therefore lead to unexpected behaviour, potentially up
to and including crashing the guest. Userspace processes will also be
able to read the current timestamp value for the domain perhaps
leaking information to those processes.
Both 32- and 64-bit ARM systems are vulnerable from Xen 4.4 onwards.
x86 systems are not vulnerable.
Chen Baozi discovered this issue as a bug which was then diagnosed by
Applying the appropriate attached patch resolves this issue.
xsa91-4.4.patch Xen 4.4.x
$ sha256sum xsa91*.patch
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