Formal Security Analysis of the AMD SEV-SNP Software Interface

AMD Secure Encrypted Virtualization technologies enable confidential computing by protecting virtual machines from highly privileged software such as hypervisors. In this work, we develop the first, comprehensive symbolic model of the software interface of the latest SEV iteration called SEV Secure Nested Paging (SEV-SNP). Our model covers remote attestation, key derivation, page swap and live migration. We analyze the security of the software interface of SEV-SNP by verifying critical secrecy, authentication, attestation and freshness properties, and find that the platform-agnostic nature of messages exchanged between SNP guests and the AMD Secure Processor firmware presents a weakness of the design. We show multiple ways of exploiting this weakness, including the compromise of attestation report integrity, and suggest slight modifications to the design which let third parties detect guest migrations to vulnerable platforms