CVE-2025-21839 KVM: x86: Load DR6 with guest value only before entering .vcpu_run() loop

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Load DR6 with guest value only before entering .vcpurun loop Move the conditional loading of hardware DR6 with the guest's DR6 value out of the core .vcpurun loop to fix a bug where KVM can load hardware with a stale...

CVE-2025-21839 KVM: x86: Load DR6 with guest value only before entering .vcpu_run() loop

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Load DR6 with guest value only before entering .vcpurun loop Move the conditional loading of hardware DR6 with the guest's DR6 value out of the core .vcpurun loop to fix a bug where KVM can load hardware with a stale...

CVE-2025-21839

CVE-2025-21839 concerns the Linux kernel KVM DR6 handling. The core issue is that DR6 value loading was handled differently from DR0–DR3, with the guest DR6 value being loaded inside the core vcpu_run loop for KVM_DEBUGREG_BP_ENABLED, and saved on VM-Exit outside the loop. This could allow a gues...