AMD SEV firmware - RMP protection bypass: MULTI-TENANT ISOLATION: An access-control failure in SEV firmware lets

Impact

MULTI-TENANT ISOLATION: An access-control failure in SEV firmware lets a malicious hypervisor bypass reverse-map table protections and break SEV-SNP guest memory integrity. The RMP is the single structure standing between a hostile host and a confidential guest's pages; a firmware-level bypass of it means the isolation you are selling is not enforced.

Who can reach it

Malicious hypervisor - host-privileged.

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.

References