Disk encryption using attestation for Confidential VMs
When a VM is confidential (CVM), the host cannot access its memory, enabling data-in-use protection. Hardware vendors like Intel (TDX) and AMD (SEV-SNP) provide the underlying technology to achieve this. The use case becomes more complex when a persistent disk is added to a CVM: the disk must also be encrypted, but how can we safely manage its encryption keys without trusting the host? We propose a mechanism to encrypt and decrypt a disk using remote attestation: the passphrase is stored in a Key Broker Service (KBS) that only releases it when the identity of the VM is verified. During the first boot, systemd-repart encrypts the root disk using a random key that is generated and stored in KBS. On subsequent boots, systemd-cryptsetup requests the same key to decrypt the disk. We present the changes we are working on to support this use case in components like KubeVirt, Trustee, and systemd-repart. We present PRs for Trustee, systemd-repart, and KubeVirt, along with a new LUKS token plugin that integrates systemd-repart and systemd-cryptsetup with KBS for key retrieval. This use case extends beyond KubeVirt and applies to any environment where confidential workloads require encrypted persistent storage, including bare metal deployments.
