CVE-2026-98720: KVM: nVMX: Force MSR bitmap refresh if runtime eVMCS controls are modified
In the Linux kernel, the following vulnerability has been resolved:
KVM: nVMX: Force MSR bitmap refresh if runtime eVMCS controls are modified
Force a refresh of the vmcs02 MSR bitmap during nested VM-Enter if the runtime eVMCS controls (pin, primary, secondary, etc.) are being updated. If L1 isn't intercepting TPR writes, runs L2 with TPR virtualization, and then runs the same L2 with TPR virtualization disabled, KVM will fail to refresh msrbitmap02 and leave TPR in passthrough mode even though TPR virtualization is disabled. I.e. failure to refresh the bitmap lets L2 (or L1 by proxy) read and write L0's TPR.
Affected Software
Event History
Frequently Asked Questions
Which environments are exposed to this issue?
The issue affects Linux kernel KVM nested virtualization using nVMX. The vulnerable scenario requires an L1 guest that does not intercept TPR writes and runs an L2 guest with TPR virtualization enabled before later running that same L2 with TPR virtualization disabled.
What could an attacker or guest do if the issue is triggered?
A stale vmcs02 MSR bitmap can leave TPR access in passthrough mode after TPR virtualization has been disabled. This allows L2, or L1 acting through L2, to read and write L0's TPR.
What is the mitigation if an updated kernel cannot be deployed immediately?
Avoid the affected nested-virtualization transition: do not run the same L2 first with TPR virtualization enabled and then with it disabled when L1 does not intercept TPR writes. Disabling or avoiding the relevant nVMX nested virtualization workload also prevents this specific condition.