virtCCA Full Disk Encryption

Full Disk Encryption (FDE) is a security technique designed to safeguard sensitive information by encrypting the entire contents of a disk partition. In standard virtual machines that do not operate in confidential environments, FDE typically employs LUKS (Linux Unified Key Setup) along with a user-provided encryption key. However, in trust execution environments such as Huawei virtCCA, the encryption key must be securely obtained from a attestation service rather than relying on direct user input.

Note: The default FDE solution is just a reference implementation. If you use other remote service, please adapt scripts in the below sections carefully.

Architecture

This section outlines a implementation for integrating FDE with Huawei virtCCA, structured into three steps.

1. Build the user environment for local verifier and generate a key file for image encryption.

2. Create an encrypted CVM image with the key file and install FDE components into its initramfs.

3. Launch a CVM based on the encrypted image through early-boot FDE workflow.

Prepare local verifier and encryption key

The FDE codes is located in the FDE_DIR=virtCCA_sdk/attestation/full-disk-encryption/grub-boot directory.

Note: we provide two attestation cases for this FDE implementation: virtCCA_sdk/attestation/samples and virtCCA_sdk/attestation/rats-tls, samples is a reference implementation (without TLS) of virtCCA attestation, while rats-tls is RATS architecture based TLS using librats.

cd ${FDE_DIR}/attestation
sh pre-fde.sh -a <samples or rats-tls>

The usage of pre-fde.sh is as follows:

  -a <attest case>: please input samples or rats-tls to specify local verifier for attestation, e.g., if input samples then `ATTEST_CASE=samples`.

Script pre-fde.sh will check the existence of virtcca-client and virtcca-server used for attestation. If absent, it will re-compile the virtCCA_sdk/attestation/sdk and virtCCA_sdk/attestation/${ATTEST_CASE}, then copy attestation apps to the current directory.

Script pre-fde.sh will check the existence of key file for image encryption. If absent, it will re-generate the key file in the current directory.

Create encrypted CVM image

We build the openEuler 24.03 LTS SP1 CVM image and validate it.

cd ${FDE_DIR}/image
sh create_fde_image.sh -i <input image> -g <image measurement reference> -o <output image> -a ${ATTEST_CASE}

The usage of create_fde_image.sh is as follows:

  -i <input image>: the initial CVM image file
  -g <image measurement reference>: the measurement reference file of CVM image, including grub image, grub.cfg file, kernel image and initramfs image 
  -a <attestation case>: the local verifier for attestation (samples or rats-tls) 
  -o <output image>: default is ${FDE_DIR}/image/virtcca-cvm-openeuler-24.03-encrypted.qcow2

Script create_fde_image.sh will encrypt the root filesystem with the encryption key. It will create a dracut module called fde and install FDE releated components into the initrd, such as attestation app virtcca-server, FDE agent fde-agent.sh and crypt binary cryptsetup. The kernel cmdline is appened with the parameter root=/dev/mapper/encroot, which represents the encrypted rootfs partition. Also /etc/fstab is updated to append the above parameter to auto-mount encrypted rootfs.

Since grub configuration file (e.g., grub.cfg) and initramfs image is changed, Script create_fde_image.sh will update the reference measurements (e.g., image_reference_measurement.json) and copy it into ${FDE_DIR}/attestation/${ATTEST_CASE} for attestation.

Default output image is ${FDE_DIR}/image/virtcca-cvm-openeuler-24.03-encrypted.qcow2, and the disk partition is as follows.

Launch CVM by early-boot FDE flow

When the CVM boot into initramfs phrase, the terminal will display CVM's IP address and virtcca-server program's port. The usrs may save these locally, for example:

# Need to change based on info of CVM terminal
export IP_ADDR=192.168.122.150 
export PORT=7220

• Step 1: Get attestation token through TMM service interface;

• Step 2: Request the encryption key with attestation token;

Script fde-agent.sh in the initrd will run /usr/bin/virtcca-server -i ${IP_ADDR} -p ${PORT} -k to achieve the above two steps.

• Step 3: User validates attestation token with local verifier, and release encryption key;

cd ${FDE_DIR}/attestation/${ATTEST_CASE}
./virtcca-client -i ${IP_ADDR} -p ${PORT} -m <measurement> -f image_reference_measurement.json -k rootfs_key.bin 

Note: <measurement> denotes the reference initial measurement of CVM, which is computed by gen_rim_ref tool (see virtCCA_sdk/attestation/rim_ref'). When ATTEST_CASE=rats-tlsplease input-r ` in the above command.

User need run the above command to finish Step 3.

• Step 4: Run cryptsetup open with encryption key to decrypt rootfs, then mount rootfs.

Script fde-agent.sh in the initrd will run cryptsetup open /dev/vda2 encroot --key-file /root/rootfs_key.bin to achieve the final Step.

After CVM boots successfully, run lsblk will display the rootfs device with FDE.