CVE-2022-49559

/// Technical description

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

KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2

Remove WARNs that sanity check that KVM never lets a triple fault for L2

escape and incorrectly end up in L1. In normal operation, the sanity

check is perfectly valid, but it incorrectly assumes that it's impossible

for userspace to induce KVM_REQ_TRIPLE_FAULT without bouncing through

KVM_RUN (which guarantees kvm_check_nested_state() will see and handle

the triple fault).

The WARN can currently be triggered if userspace injects a machine check

while L2 is active and CR4.MCE=0. And a future fix to allow save/restore

of KVM_REQ_TRIPLE_FAULT, e.g. so that a synthesized triple fault isn't

lost on migration, will make it trivially easy for userspace to trigger

the WARN.

Clearing KVM_REQ_TRIPLE_FAULT when forcibly leaving guest mode is

tempting, but wrong, especially if/when the request is saved/restored,

e.g. if userspace restores events (includi

/// 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