KVM Vulnerability in Linux Kernel Affecting x86 Systems

CVE-2025-21839

Summary

In the Linux kernel's KVM module, a flaw exists related to the handling of the debug register DR6 on x86 systems. The vulnerability arises when the KVM module loads the hardware DR6 with stale values during the .vcpu_run loop process. This mismanagement can lead to unintended consequences in virtualized environments, particularly during nested virtualization setups, where the timing of hardware and guest operations can cause the retrieval of incorrect DR6 values. The issue primarily affects performance and accuracy in debugging and monitoring scenarios within virtualized deployments. Proper configurations and updates are necessary to resolve this issue.

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