AMD IOMMU - nested page table entry faults bypass SEV-SNP RMP checks: MULTI-TENANT ISOLATION: The IOMMU mishandles

Impact

MULTI-TENANT ISOLATION: The IOMMU mishandles invalid nested page table entries, letting a privileged attacker induce PTE faults that bypass SEV-SNP RMP enforcement and tamper with confidential guest memory. Same failure shape as the DTE variant and disclosed alongside it - the IOMMU's error paths are where RMP enforcement leaks.

Who can reach it

Hypervisor-privileged attacker driving DMA through the IOMMU.

What to do

Fixed in AMD SEV firmware / AGESA and reaches you as an OEM SBIOS package - AMD hands AGESA to Dell, HPE, Supermicro, Lenovo and the ODMs, who each requalify before shipping BIOS. **Budget one to six months of OEM lag**, longer on older platforms and sometimes never on end-of-support SKUs. Applying it means draining the host and doing a full power cycle. Because the fix moves the platform's reported SEV-SNP TCB version, you must also pull fresh VCEK certificates from AMD's Key Distribution Service and update any attestation policy your tenants pin - otherwise guests will start failing launch validation the moment the BIOS lands. Some SEV firmware can alternatively be staged from linux-firmware (amd/amd_sev_*.sbin) and committed via the ccp driver at boot, which is faster than waiting on BIOS - check whether your platform supports firmware hot-load before assuming the OEM is the only route. Patch alongside the DTE variant; they ship together.

References