Executive brief
A vulnerability in the Linux kernel's virtualization component (KVM) can cause virtual machines to crash or fail to start on certain hardware configurations. This issue primarily affects older processors or environments where one virtual machine is running inside another (nested virtualization). While it does not directly expose data, it can lead to service outages and system instability for affected virtualized workloads.
Technical details
A vulnerability in KVM's x86 implementation occurs because the TPR_THRESHOLD field in the VMCS is not recomputed when a Processor Priority Register (PPR) update does not result in a pending deliverable interrupt. Specifically, an optimization in handle_tpr_below_threshold() calls apic_update_ppr() without raising KVM_REQ_EVENT if no new interrupts are pending, leaving a stale, high TPR_THRESHOLD. This violates Intel SDM requirements for VM-execution control fields when virtual-interrupt delivery is disabled. The resulting inconsistency causes a VM entry failure with hardware error 0x7. The fix ensures kvm_lapic_update_cr8_intercept() is called unconditionally on PPR updates to synchronize the threshold.
Affected products
- Linux Linux Kernel eb90f3417a0c to ff9c4c642888
Timeline
- 2026-06-18: disclosed: Initial patch submission
- 2026-07-25: advisory: CVE published