Trust provides secure unattended boot of systems (hardware and virtual machines). It protects the keys for encrypted filesystem, as well as a per-machine provisioned certificate/keypair. It ensures that only an OS (kernel, initrd (initial filesystem), and kernel command-line) which has been signed by you will be able to read these keys.
Trust is currently implemented using a combination of UEFI secureboot and TPM2. Other hardware assisted architectures are also possible, and should be easy to implement as alternative implementations of the Truststore interface.
The following steps implement the trust workflow:
- 'trust provision' - This step takes a key and certificate which the machine can use to uniquely and securely identify itself, e.g. to form a cluster with peers.
- 'trust preinit' - This is run as the first step of an OS install sequence. it will generate a new LUKS passphrase, overwrite the existing one on the TPM, and load the new LUKS passphrase in the root user keyring for use by the installer. It will not load any pre-existing LUKS passphrase, or load the provisioned key.
- 'trust setup' - This is run during the signed initrd to copy the secrets out of the TPM. Currently the LUKS passphrase is stored in root user keyring, and the provisioned key and certificate are stored in a private tmpfs. Early (signed) userspace can, before enabling network, mount all filesystems, and remove the LUKS key from keyring. It can also load the provisioned key into the TPM and unmount the tmpfs.
-
This is based on the concepts and scripts published at https://github.com/puzzleos/tpm_eapol_scripts and presented at LSS 2021 by Paul Moore and Joy Latten at https://www.youtube.com/watch?v=wfJDmfPP1OA).
-
mos ('machine-os') will and mb ('machine-builder') will implement the proper placement of the trust commands, as well as the secure bootstrap of userspace.