CVE-2026-64513: KVM: x86: Unconditionally recompute CR8 intercept on PPR update
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86: Unconditionally recompute CR8 intercept on PPR update
The TPRTHRESHOLD 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 handletprbelowthreshold(). Commit eb90f3417a0c ("KVM: vmx: speed up TPR below threshold vmexits") optimized this function by calling apicupdateppr() instead of raising KVMREQEVENT. apicupdateppr() then raises KVMREQEVENT if there is a pending, deliverable interrupt.
However, if there are no new interrupts pending, apicupdateppr() does not issue the request. Thus, kvmlapicupdatecr8intercept() and vmxupdatecr8intercept() are not called before VM entry, which results in a high, stale TPRTHRESHOLD. 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 TPRTHRESHOLD 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 kvmlapicupdatecr8intercept() if apicupdateppr() does not find a deliverable interrupt (and thus does not raise KVMREQEVENT). Remove calls to kvmlapicupdatecr8intercept() on paths that end up in apicupdateppr(), 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 TPRTHRESHOLD on VMX or CR8 intercepts on SVM).
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1012.12~24.04.1 - Upgrade
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ubuntu/linux-azure-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-azure-fde-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13~24.04.1 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1011.11~24.04.1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-31.31~24.04.1 - Upgrade
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ubuntu/linux-nvidia-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1018.18~24.04.1 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1011.11~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-31.31.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-31.31 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1012.12 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1011.11 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1006.7 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 7.0.0-1018.18 - Upgrade
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ubuntu/linux-nvidia-bosto a version that resolves this vulnerability.Fixed in 7.0.0-2018.18 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1011.11 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 7.0.0-1019.19 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-31.31.1 - Upgrade
Upgrade
ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-31.31.1 - Compensating control
In KVM, call kvm_lapic_update_cr8_intercept() when apic_update_ppr() does not find a deliverable interrupt and therefore does not raise KVM_REQ_EVENT.
- Compensating control
Remove calls to kvm_lapic_update_cr8_intercept() on code paths that call apic_update_ppr(), because those calls become redundant.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-64513?
CVE-2026-64513 has a risk rating of 27, indicating a high severity level.
How do I fix CVE-2026-64513?
To fix CVE-2026-64513, update your Linux kernel to the latest version where this vulnerability is resolved.
What systems are affected by CVE-2026-64513?
CVE-2026-64513 affects KVM-based virtualization environments running on x86 architecture in the Linux kernel.
What does CVE-2026-64513 impact?
CVE-2026-64513 impacts the handling of TPR_THRESHOLD in VMX which can lead to improper VM exits.
Is CVE-2026-64513 being actively exploited?
As of now, there is no public indication that CVE-2026-64513 is being actively exploited in the wild.