| Description: | The prepare_vmcs02 function in arch/x86/kvm/vmx.c in the Linux kernel through 4.13.3 does not ensure that the "CR8-load exiting" and "CR8-store exiting" L0 vmcs02 controls exist in cases where L1 omits the "use TPR shadow" vmcs12 control, which allows KVM L2 guest OS users to obtain read and write access to the hardware CR8 register. It was discovered that the nested KVM implementation in the Linux kernel in some situations did not properly prevent second level guests from reading and writing the hardware CR8 register. A local attacker in a guest could use this to cause a denial of service (system crash).
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