Linux kernel KVM arm64: MOPS exception handler writes synthetic vEL2 CPSR straight into hardware

Impact

On arm64 hosts running KVM, the MOPS exception rewind path modified the synthetic vcpu_cpsr() value and wrote it directly to hardware without translating it for nested virtualization, so a guest using vEL2 could drive the host into inconsistent single-step/exception state. NVD rates it 8.8 with changed scope (AV:L/PR:L, C/I/A High), i.e. a local guest-side actor affecting the host. This matters only on arm64 GPU hosts - Grace-based GB200/GH200 head nodes and arm64 KVM hypervisors - and only where nested virtualization is in use; nested virt on arm64 is not a default configuration, and x86 GPU nodes are not affected at all. For an operator the cost is not the exploit odds but the fix: it lands in the host kernel, so the hypervisor must be rebooted and every GPU VM on it drained first.

Who can reach it

A local actor on an arm64 KVM host, in practice a guest VM that can trigger MOPS exceptions while running with KVM nested virtualization (vEL2) enabled. No remote path and no unauthenticated path; authentication is whatever is needed to run code in a guest or locally on the host.

What to do

Fixed in the Linux stable trees (four stable commits listed in the record). Pick up the vendor kernel that carries the fix, then reboot each arm64 hypervisor - which means draining its GPU VMs first, so schedule it with normal node-reboot maintenance rather than as an emergency. If you run no arm64 KVM hosts, or run them without nested virtualization, there is nothing to do. No upstream mitigation other than not enabling nested virt is described in the record.

References

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