AMD CPU - stale TLB entries in SEV-SNP guests: MULTI-TENANT ISOLATION: A silicon bug lets a local admin-privileged

Impact

MULTI-TENANT ISOLATION: A silicon bug lets a local admin-privileged attacker run an SEV-SNP guest against stale TLB entries. The guest executes with translations that no longer reflect the real page mappings, which the host can steer - a data-integrity attack on a confidential VM that leaves no trace in the guest, since from inside the VM the memory simply reads wrong.

Who can reach it

Local, admin-privileged host attacker targeting a confidential guest.

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