[A/B/C] CVE-2018-12904 - Possible priv escalation and DoS in nested KVM

[Tyler Hicks]

Description:
 In arch/x86/kvm/vmx.c in the Linux kernel before 4.17.2, when nested
 virtualization is used, local attackers could cause L1 KVM guests to
 VMEXIT, potentially allowing privilege escalations and denial of service
 attacks due to lack of checking of CPL.
Notes:
 tyhicks> Ubuntu kernels do not enable nested KVM virtualization by default and
  are unaffected by this flaw in the default configuration. To ensure that
  nested virtualization is not enabled, verify that the
  /sys/module/kvm_intel/parameters/nested file contains "N".
Bugs:
 https://bugs.chromium.org/p/project-zero/issues/detail?id=1589
Priority: low
Discovered-by: Felix Wilhelm

Tyler