Linux kernel (arch/x86/kvm): A guest that is in SMM and then triple-faults makes SVM take the SHUTDOWN intercept and

Impact

A guest that is in SMM and then triple-faults makes SVM take the SHUTDOWN intercept and reset the vCPU without first forcing it out of SMM, leaving host-side vCPU state in an architecturally impossible configuration. The same omission in the nested path was previously a use-after-free, and the kernel CNA rates this one as a scope-changing confidentiality, integrity and availability break.

Who can reach it

Guest-driven on AMD hosts and reproduced by syzkaller with nothing but a VM and one vCPU: enter SMM (a guest can direct an SMI at itself through the emulated local APIC, or the VMM's KVM_SMI path is used) and then execute instructions that cascade into a triple fault. No passthrough device and no host privilege required.

What to do

Update to a stable kernel with the linked fix; the record points at the 5.16 and 6.1 lines, so take the point release on your branch that contains commit e9b28bc65fd3. No meaningful interim control - SMM emulation cannot be disabled per tenant.

References