QEMU VAPIC hypercall lets a privileged guest write into locked SMRAM and run code in SMM

Impact

The VAPIC setup hypercall does not check that the writable RAM alias it creates stays inside the option ROM window, so a guest with root can point that alias at locked SMRAM. That defeats the chipset D_LCK protection and lets the guest inject code into System Management Mode memory - the most privileged execution context on the machine, below the hypervisor. On a GPU cloud that rents VMs with passthrough accelerators, this is a tenant-to-host trust boundary break: SMM code persists across guest reboots and is invisible to the host kernel, so a compromised node cannot be trusted again by wiping the guest. Red Hat scores it 8.2 with scope change, reflecting the escape out of the VM.

Who can reach it

A privileged (root) user inside a guest on a Q35/KVM machine type. No access to the host or the management network is needed; local guest privilege is enough.

What to do

Apply the QEMU update from your distribution when it ships - Red Hat tracks this for RHEL 6 through 10, RHEL for NVIDIA 26 and OpenShift Container Platform 4, and the upstream fix is tracked in the QEMU project work item. Updating QEMU requires restarting or live-migrating every guest on the host to pick up the new binary, so plan an evacuation pass across the fleet rather than an in-place restart. Until patched, guests whose root is untrusted should not run on hosts you need to keep clean.

References

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