AMD Secure Processor - TOCTOU race: MULTI-TENANT ISOLATION: A time-of-check-to-time-of-use race in the ASP lets

Impact

MULTI-TENANT ISOLATION: A time-of-check-to-time-of-use race in the ASP lets an attacker swap a value between validation and use, corrupting secure-processor memory. Winning the race costs integrity, confidentiality or availability of the ASP depending on what gets corrupted - and the ASP is the component vouching for the node's confidential-computing posture.

Who can reach it

Local. Requires the attacker to run concurrently with the ASP operation and to be able to modify the memory being checked, i.e. host-privileged code.

What to do

Fixed in AMD reference firmware (AGESA / SEV firmware) and delivered to you only as an OEM SBIOS/BIOS package - Dell, HPE, Supermicro, Lenovo, Gigabyte and the ODMs each rebuild and requalify AMD's AGESA drop before it ships. **Expect months, not weeks**: AMD publishes the bulletin, the OEM ships BIOS somewhere between one and six months later, and for platforms past their support window it may never arrive at all. Applying it is a full node power cycle with the host drained - not a driver reload, not a live patch. Track it as a firmware campaign per server SKU, not per kernel version, and verify afterwards by reading back the SMU/PSP firmware version rather than trusting the BIOS revision string. Because this sits inside the SEV-SNP trust boundary, the update also moves the platform's reported TCB version: after patching you must refresh VCEK certificates from AMD's KDS and update whatever attestation policy your tenants (or your own confidential-VM control plane) pin against, or every guest launch will start failing validation.

References