KVM: x86: Unconditionally recompute CR8 intercept on PPR update

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Summary

CVECVE-2026-64513
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-25 10:17:37 UTC
Updated2026-07-25 10:17:37 UTC
DescriptionIn 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).

Risk And Classification

EPSS: 0.001710000 probability, percentile 0.067070000 (date 2026-07-29)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected eb90f3417a0cc4880e979ccc84e41890d410ea5b ff9c4c6428883182960cfe5c78928f0896d80ebc git Not specified
CNA Linux Linux affected eb90f3417a0cc4880e979ccc84e41890d410ea5b 8c8e8ac22ee17d52f9eb2bc814bca7fab90fb8df git Not specified
CNA Linux Linux affected eb90f3417a0cc4880e979ccc84e41890d410ea5b bb365a506b1e6fb050c0fceaad354fe395385ef0 git Not specified
CNA Linux Linux affected 4.11 Not specified
CNA Linux Linux unaffected 4.11 semver Not specified
CNA Linux Linux unaffected 6.18.39 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.4 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/ff9c4c6428883182960cfe5c78928f0896d80ebc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/bb365a506b1e6fb050c0fceaad354fe395385ef0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/8c8e8ac22ee17d52f9eb2bc814bca7fab90fb8df 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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