An issue was discovered in Linux: KVM through Improper handling of
VM_IO|VM_PFNMAP vmas in KVM can bypass RO checks and can lead to pages
being freed while still accessible by the VMM and guest. This allows users
with the ability to start and control a VM to read/write random pages of
memory and can result in local privilege escalation.

It was discovered that the KVM hypervisor implementation in the Linux
kernel did not properly perform reference counting in some situations,
leading to a use-after-free vulnerability. An attacker who could start and
control a VM could possibly use this to expose sensitive information or
execute arbitrary code.