CVE-2015-7513 Kernel: kvm: divide by zero issue leads to DoS

[P J P <ppandit () redhat com>]

   Hello,

Linux kernel built with the KVM virtualisation support(CONFIG_KVM) is 
vulnerable to a divide by zero issue. It occurs in the KVM module's 
Programmable Interval Timer(PIT) emulation, when PIT counters for channel 1 or 
2 are set to zero(0) and a privileged user inside guest attempts to read 
those.

A privileged guest user with access to PIT I/O ports, could use this issue to 
crash the host kernel resulting in DoS.

Upstream patch:
---------------
  -> https://git.kernel.org/linus/0185604c2d82c560dab2f2933a18f797e74ab5a8

Reference:
----------
  -> https://bugzilla.redhat.com/show_bug.cgi?id=1284847

It requires host user to set the PIT channel counters to zero(0).

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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