CVE-2026-43483 (GCVE-0-2026-43483)

Vulnerability from cvelistv5 – Published: 2026-05-13 15:08 – Updated: 2026-05-13 15:08
VLAI?
Title
KVM: SVM: Set/clear CR8 write interception when AVIC is (de)activated
Summary
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::V_TPR 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 TPR_THRESHOLD 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 update_cr8_intercept(), 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 avic_deactivate_vmcb. - Paolo]
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 3bbf3565f48ce3999b5a12cde946f81bd4475312 , < a4123fe5d9122eef9852e4921f7cc463420f30d4 (git)
Affected: 3bbf3565f48ce3999b5a12cde946f81bd4475312 , < 816fa1dfae4532e851b1fe6b2434c753ecbd86c7 (git)
Affected: 3bbf3565f48ce3999b5a12cde946f81bd4475312 , < 01651e7751edbbc0fb4598f8367a3dabcfc8c182 (git)
Affected: 3bbf3565f48ce3999b5a12cde946f81bd4475312 , < ba3bca40f9f25c053f69413e5f4a41dd0fd762bf (git)
Affected: 3bbf3565f48ce3999b5a12cde946f81bd4475312 , < 737410b32bd615b321da4fbeda490351b9af5e8b (git)
Affected: 3bbf3565f48ce3999b5a12cde946f81bd4475312 , < 87d0f901a9bd8ae6be57249c737f20ac0cace93d (git)
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Linux Linux Affected: 4.7
Unaffected: 0 , < 4.7 (semver)
Unaffected: 6.1.167 , ≤ 6.1.* (semver)
Unaffected: 6.6.130 , ≤ 6.6.* (semver)
Unaffected: 6.12.78 , ≤ 6.12.* (semver)
Unaffected: 6.18.19 , ≤ 6.18.* (semver)
Unaffected: 6.19.9 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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            "arch/x86/kvm/svm/avic.c",
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Set/clear CR8 write interception when AVIC is (de)activated\n\nExplicitly set/clear CR8 write interception when AVIC is (de)activated to\nfix a bug where KVM leaves the interception enabled after AVIC is\nactivated.  E.g. if KVM emulates INIT=\u003eWFS while AVIC is deactivated, CR8\nwill remain intercepted in perpetuity.\n\nOn its own, the dangling CR8 intercept is \"just\" a performance issue, but\ncombined with the TPR sync bug fixed by commit d02e48830e3f (\"KVM: SVM:\nSync TPR from LAPIC into VMCB::V_TPR even if AVIC is active\"), the danging\nintercept is fatal to Windows guests as the TPR seen by hardware gets\nwildly out of sync with reality.\n\nNote, VMX isn\u0027t affected by the bug as TPR_THRESHOLD is explicitly ignored\nwhen Virtual Interrupt Delivery is enabled, i.e. when APICv is active in\nKVM\u0027s world.  I.e. there\u0027s no need to trigger update_cr8_intercept(), this\nis firmly an SVM implementation flaw/detail.\n\nWARN if KVM gets a CR8 write #VMEXIT while AVIC is active, as KVM should\nnever enter the guest with AVIC enabled and CR8 writes intercepted.\n\n[Squash fix to avic_deactivate_vmcb. - Paolo]"
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}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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