In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Unconditionally recompute CR8 intercept on PPR update The… (CVE-2026-64513)
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Unconditionally recompute CR8 intercept on PPR update The TPR_THRESHOLD field in the VMCS is used by VMX to induce VM exits when the guest's virtual TPR falls under the specified threshold, allowing KVM to inject previously masked interrupts. KVM handles these VM exits in handle_tpr_below_threshold(). Commit eb90f3417a0c ("KVM: vmx: speed up TPR below threshold vmexits") optimized this function by calling apic_update_ppr() instead of raising KVM_REQ_EVENT. apic_update_ppr() then raises KVM_REQ_EVENT if there is a pending, deliverable interrupt. However, if there are no new interrupts pending, apic_update_ppr() does not issue the request. Thus, kvm_lapic_update_cr8_intercept() and vmx_update_cr8_intercept() are not called before VM entry, which results in a high, stale TPR_THRESHOLD. This is problematic due to the following sentence in 28.2.1.1 "VM-Execution Control Fields" in the SDM: The following check is performed if the “use TPR shadow” VM-execution control is 1 and the “virtualize APIC accesses” and “virtual-interrupt delivery” VM-execution controls are both 0: the value of bits 3:0 of the TPR threshold VM-execution control field should not be greater than the value of bits 7:4 of VTPR. This error condition is typically not observed when KVM runs on a bare metal system because modern processors support APICv, which enables virtual-interrupt delivery, and which KVM uses when possible. This causes the processor to no longer generate TPR-below-threshold exits and to no longer check TPR_THRESHOLD on entry. However, when running on older platforms, or under nested virtualization on a hypervisor that does not support virtual-interrupt delivery and enforces this check (like Hyper-V) this can cause a VM entry failure with hardware error 0x7, as seen in [1]. Call kvm_lapic_update_cr8_intercept() if apic_update_ppr() does not find a deliverable interrupt (and thus does not raise KVM_REQ_EVENT). Remove calls to kvm_lapic_update_cr8_intercept() on paths that end up in apic_update_ppr(), as they now become redundant. This ensures that any path that updates the guest's PPR also figures out if KVM needs to wait for a TPR change (using TPR_THRESHOLD on VMX or CR8 intercepts on SVM).
AI Analysis
Technical Summary
The vulnerability in the Linux kernel KVM x86 virtualization arises from the optimization of the handle_tpr_below_threshold() function, where apic_update_ppr() replaced raising KVM_REQ_EVENT. If no new interrupts are pending, apic_update_ppr() does not raise KVM_REQ_EVENT, causing kvm_lapic_update_cr8_intercept() and vmx_update_cr8_intercept() not to be called before VM entry. This results in a stale TPR_THRESHOLD value, violating VMX execution control checks and causing VM entry failures with hardware error 0x7 on systems lacking APICv support or under nested virtualization on hypervisors like Hyper-V. The remediation involves calling kvm_lapic_update_cr8_intercept() when apic_update_ppr() does not find deliverable interrupts, ensuring proper CR8 intercept updates on all PPR update paths.
Potential Impact
This vulnerability can cause virtual machine entry failures with hardware error 0x7 on affected systems, particularly older hardware without APICv support or nested virtualization environments on hypervisors that enforce strict VMX execution control checks. This may lead to denial of service for virtual machines relying on KVM on such platforms. There is no indication of code execution or privilege escalation from the provided data.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The description indicates that a code fix has been implemented in the Linux kernel to address this issue by ensuring CR8 intercepts are updated correctly on all PPR update paths. Users should monitor official Linux kernel advisories and update to fixed kernel versions once available. No alternative mitigations are specified.
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Unconditionally recompute CR8 intercept on PPR update The… (CVE-2026-64513)
Description
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Unconditionally recompute CR8 intercept on PPR update The TPR_THRESHOLD field in the VMCS is used by VMX to induce VM exits when the guest's virtual TPR falls under the specified threshold, allowing KVM to inject previously masked interrupts. KVM handles these VM exits in handle_tpr_below_threshold(). Commit eb90f3417a0c ("KVM: vmx: speed up TPR below threshold vmexits") optimized this function by calling apic_update_ppr() instead of raising KVM_REQ_EVENT. apic_update_ppr() then raises KVM_REQ_EVENT if there is a pending, deliverable interrupt. However, if there are no new interrupts pending, apic_update_ppr() does not issue the request. Thus, kvm_lapic_update_cr8_intercept() and vmx_update_cr8_intercept() are not called before VM entry, which results in a high, stale TPR_THRESHOLD. This is problematic due to the following sentence in 28.2.1.1 "VM-Execution Control Fields" in the SDM: The following check is performed if the “use TPR shadow” VM-execution control is 1 and the “virtualize APIC accesses” and “virtual-interrupt delivery” VM-execution controls are both 0: the value of bits 3:0 of the TPR threshold VM-execution control field should not be greater than the value of bits 7:4 of VTPR. This error condition is typically not observed when KVM runs on a bare metal system because modern processors support APICv, which enables virtual-interrupt delivery, and which KVM uses when possible. This causes the processor to no longer generate TPR-below-threshold exits and to no longer check TPR_THRESHOLD on entry. However, when running on older platforms, or under nested virtualization on a hypervisor that does not support virtual-interrupt delivery and enforces this check (like Hyper-V) this can cause a VM entry failure with hardware error 0x7, as seen in [1]. Call kvm_lapic_update_cr8_intercept() if apic_update_ppr() does not find a deliverable interrupt (and thus does not raise KVM_REQ_EVENT). Remove calls to kvm_lapic_update_cr8_intercept() on paths that end up in apic_update_ppr(), as they now become redundant. This ensures that any path that updates the guest's PPR also figures out if KVM needs to wait for a TPR change (using TPR_THRESHOLD on VMX or CR8 intercepts on SVM).
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in the Linux kernel KVM x86 virtualization arises from the optimization of the handle_tpr_below_threshold() function, where apic_update_ppr() replaced raising KVM_REQ_EVENT. If no new interrupts are pending, apic_update_ppr() does not raise KVM_REQ_EVENT, causing kvm_lapic_update_cr8_intercept() and vmx_update_cr8_intercept() not to be called before VM entry. This results in a stale TPR_THRESHOLD value, violating VMX execution control checks and causing VM entry failures with hardware error 0x7 on systems lacking APICv support or under nested virtualization on hypervisors like Hyper-V. The remediation involves calling kvm_lapic_update_cr8_intercept() when apic_update_ppr() does not find deliverable interrupts, ensuring proper CR8 intercept updates on all PPR update paths.
Potential Impact
This vulnerability can cause virtual machine entry failures with hardware error 0x7 on affected systems, particularly older hardware without APICv support or nested virtualization environments on hypervisors that enforce strict VMX execution control checks. This may lead to denial of service for virtual machines relying on KVM on such platforms. There is no indication of code execution or privilege escalation from the provided data.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The description indicates that a code fix has been implemented in the Linux kernel to address this issue by ensuring CR8 intercepts are updated correctly on all PPR update paths. Users should monitor official Linux kernel advisories and update to fixed kernel versions once available. No alternative mitigations are specified.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-2vpm-g563-9g48
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-64513"]
- Ecosystems
- []
- Database Specific Severity
- null
- Cvss Version
- null
Threat ID: 6a6542069c2644c7f80820cd
Added to database: 07/25/2026, 23:08:54 UTC
Last enriched: 07/25/2026, 23:15:46 UTC
Last updated: 09/07/2026, 10:52:10 UTC
Views: 59
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