AMD IOMMU access control - SEV-SNP RMP check bypass (AMD-SB-3009): MULTI-TENANT ISOLATION: An IOMMU access-control flaw

Impact

MULTI-TENANT ISOLATION: An IOMMU access-control flaw lets a privileged attacker bypass reverse-map table checks, undermining SEV-SNP guest memory protection. One of a family of IOMMU-mediated RMP bypasses - the RMP guards CPU accesses well, and the recurring weakness is device accesses arriving through the IOMMU's error and edge-case paths.

Who can reach it

Privileged attacker with a compromised hypervisor, driving DMA.

What to do

Fixed in AMD PI/AGESA firmware and delivered only as an OEM SBIOS package - AMD ships the PI drop to Dell, HPE, Supermicro, Lenovo and the ODMs, who each requalify before releasing BIOS. **Budget one to six months of OEM lag**, and note that several CVEs in this batch are marked 'no fix planned' on Naples (EPYC 7001) - for those the only remediation is retiring the hardware. Applying it means cordon, drain and a full power cycle per node; there is no driver reload, no live patch and no VBIOS step. Because this touches the SEV-SNP trust boundary, the update moves the platform TCB version: refresh VCEK certificates from AMD's KDS and update tenant attestation policy, or confidential guest launches will fail immediately after the BIOS lands. Patch as a set with the other IOMMU/RMP bypasses rather than individually - they share firmware releases and any one of them reopens the class.

References