CVE-2026-43483: KVM: SVM: Set/clear CR8 write interception when AVIC is (de)activated
In the Linux kernel, the following vulnerability has been resolved:
KVM: SVM: Set/clear CR8 write interception when AVIC is (de)activated
Explicitly set/clear CR8 write interception when AVIC is (de)activated to fix a bug where KVM leaves the interception enabled after AVIC is activated. E.g. if KVM emulates INIT=>WFS while AVIC is deactivated, CR8 will remain intercepted in perpetuity.
On its own, the dangling CR8 intercept is "just" a performance issue, but combined with the TPR sync bug fixed by commit d02e48830e3f ("KVM: SVM: Sync TPR from LAPIC into VMCB::VTPR even if AVIC is active"), the danging intercept is fatal to Windows guests as the TPR seen by hardware gets wildly out of sync with reality.
Note, VMX isn't affected by the bug as TPRTHRESHOLD is explicitly ignored when Virtual Interrupt Delivery is enabled, i.e. when APICv is active in KVM's world. I.e. there's no need to trigger updatecr8intercept(), this is firmly an SVM implementation flaw/detail.
WARN if KVM gets a CR8 write #VMEXIT while AVIC is active, as KVM should never enter the guest with AVIC enabled and CR8 writes intercepted.
[Squash fix to avicdeactivatevmcb. - Paolo]
Affected Software
Event History
Frequently Asked Questions
Which KVM environments are affected?
The issue is specific to KVM's SVM implementation when AVIC is used. VMX is not affected because it ignores TPR_THRESHOLD when Virtual Interrupt Delivery/APICv is enabled.
What conditions make the impact severe for guests?
A lingering CR8 write intercept is normally a performance issue. When combined with the separate TPR synchronization bug referenced in the fix, it can cause the hardware TPR to diverge from reality and be fatal to Windows guests.
What access is required according to the supplied CVSS vector?
The CVSS vector indicates local attack access, low privileges, and no user interaction. The stated impact is availability only, with no confidentiality or integrity impact.
How can operators identify the invalid interception state?
KVM warns if it receives a CR8-write VMEXIT while AVIC is active. According to the fix description, KVM should never enter a guest with both AVIC enabled and CR8 writes intercepted.