CVE-2024-39483

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

KVM: SVM: WARN on vNMI + NMI window iff NMIs are outright masked

When requesting an NMI window, WARN on vNMI support being enabled if and

only if NMIs are actually masked, i.e. if the vCPU is already handling an

NMI. KVM's ABI for NMIs that arrive simultanesouly (from KVM's point of

view) is to inject one NMI and pend the other. When using vNMI, KVM pends

the second NMI simply by setting V_NMI_PENDING, and lets the CPU do the

rest (hardware automatically sets V_NMI_BLOCKING when an NMI is injected).

However, if KVM can't immediately inject an NMI, e.g. because the vCPU is

in an STI shadow or is running with GIF=0, then KVM will request an NMI

window and trigger the WARN (but still function correctly).

Whether or not the GIF=0 case makes sense is debatable, as the intent of

KVM's behavior is to provide functionality that is as close to real

hardware as possible. E.g. if two NMIs are sent in quick succession, the

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References