AMD SEV-SNP - debug exception delivery to guests: A privileged attacker can suppress delivery of debug exceptions

Impact

A privileged attacker can suppress delivery of debug exceptions to SEV-SNP guests. The guest does not get debug information it expects, which is mostly an availability and observability problem - but for a guest that relies on debug exceptions as part of a self-protection or integrity-checking scheme, silently swallowing them removes that check.

Who can reach it

Privileged host attacker against 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. Low priority relative to the RMP-bypass and microcode issues; batch it into the next BIOS wave.

References