AMD SEV-ES Trusted Memory Region - SNP guest memory integrity: MULTI-TENANT ISOLATION: A bug in the SEV-ES Trusted

Impact

MULTI-TENANT ISOLATION: A bug in the SEV-ES Trusted Memory Region handling costs memory integrity for SNP-active VMs. The TMR is the region the SEV firmware itself works in; a defect there means the component enforcing confidential-VM isolation can have its own working memory disturbed, and SNP guests lose the integrity guarantee they were sold.

Who can reach it

Requires host/hypervisor privilege on a machine running SNP guests.

What to do

Fixed in AMD reference firmware (AGESA / PSP / SEV firmware) and delivered only as an OEM SBIOS/BIOS package - Dell, HPE, Supermicro, Lenovo and the ODMs each rebuild and requalify AMD's AGESA drop before shipping. **Expect one to six months of OEM lag**, and on end-of-support platforms expect nothing. Applying it is a drain plus full power cycle, not a driver reload. Verify by reading back the PSP/SMU firmware version afterwards rather than trusting the BIOS version string. This sits inside the SEV-SNP trust boundary, so the update moves the platform's reported TCB version: refresh VCEK certificates from AMD's KDS and update any attestation policy your tenants pin, or confidential guest launches will start failing right after the BIOS lands.

References