AMD CPU pipeline configuration - SEV-SNP guest stack pointer corruption: MULTI-TENANT ISOLATION: A write-what-where

Impact

MULTI-TENANT ISOLATION: A write-what-where condition in CPU pipeline configuration lets an admin-privileged attacker corrupt the stack pointer inside an SEV-SNP guest. Corrupting a guest's stack pointer from outside is a control-flow attack on a VM whose memory the host is not supposed to be able to touch - a route to steering execution inside a confidential workload.

Who can reach it

Local, admin-privileged host attacker.

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