rpi-sb-provisioner

Secure Boot typically refers to an authenticated boot chain, where from the moment the main processor starts every components authenticates the next component before allowing it to execute.

In order to simplify the mass deployment of secure boot for Raspberry Pi Devices, we have introduced a new tool, the Raspberry Pi Secure Boot Provisioner.

This tool, referred to later in the document as rpi-sb-provisioner, is designed to fully automate:

• enforcing secure boot on Raspberry Pi devices

• the programming of firmware

• the programming of signing and device encryption keys

• tying the device encryption key to the storage device

• inserting a customer-supplied (created with pi-gen) operating system into an encrypted container on the storage device

For more information on creating an OS based on Raspberry Pi OS in pi-gen, consult the pi-gen repository at https://github.com/RPi-Distro/pi-gen

NOTE: This tool is under active development. Please report issues at https://github.com/raspberrypi/rpi-sb-provisioner

Requirements for rpi-sb-provisioner

Required hardware for the provisioning system

• A Raspberry Pi 5 (or other 64-bit Raspberry Pi device)

• An official Raspberry Pi 5 Power Supply

• An installation of Raspberry Pi OS Bookworm, or later

• At least 32GB of storage, for temporary working files

• For provisoning Raspberry Pi Compute Module 4:

  • A USB-A to microUSB-B cable

  • A Raspberry Pi Compute Module 4 IO Board

  • A single Jumper Wire

• For provisioning Raspberry Pi 5:

  • A USB-A to USB-C cable

Hardware configuration

Connect your Raspberry Pi 5 to your Raspberry Pi Compute Module 4 IO Board as illustrated. Grey cables supply power, Red supplies data.

Figure 1. A correctly connected provisioning set-up

Software configuration

rpi-sb-provisioner is provided from the Raspberry Pi OS APT repositories, and can be installed in the usual manner.

First, ensure you are running an up-to-date version of Raspberry Pi OS on your provisioning server:

$ sudo apt update && sudo apt full-upgrade -y

Now, install the rpi-sb-provisioner package from the releases area:

$ sudo dpkg -i rpi-sb-provisioner_foo.deb
$ sudo apt --fix-broken install
$ sudo reboot now

Next, you will have to configure rpi-sb-provisioner by using the TUI. In a terminal, run:

$ config.sh

Warning

This will not work if you have not reboot after installing the package!

Warning

`rpi-sb-provisioner' must be installed with `--install-suggests' for `config.sh' to work. This will require installation of `python3-textual' and `python3-rich' from Debian’s Trixie release.

Running this command will open up a full screen text UI. The TUI supports mouse input or keyboard navigation! Each of the boxes contains a name, text entry and help button. The steps for editing each parameter are as follows:

Figure 2. A parameter entry area

1 - Click or use tab to click the help button to view the information about the parameter

2 - Navigate to the text field and enter the value you wish

3 - To stage this value for writing, you must click return on your keyboard. If the value is successfully verified, then the field will change color to green and a tick should appear. If validation fails, a warning popup should appear with some help text. A cross will also appear next to the parameter name.

Figure 3. A successfully verified parameter

4 - Repeat the above steps to complete your required parameters (some are optional).

5 - Write to the configuration file by pressing the Write verified params to config file button at the bottom of the screen

Once you have followed all those steps, rpi-sb-provisioner should be correctly configured and ready to run.

Configuration fields

Configure rpi-sb-provisioner by using the following fields in /etc/rpi-sb-provisioner/config

CUSTOMER_KEY_FILE_PEM

Optional, mandatory if CUSTOMER_KEY_PKCS11_NAME is not set

The fully qualified path to your signing key, encoded in PEM format. This file is expected to contain an RSA 2048-bit Private Key.

Warning

This file should be considered key material, and should be protected while at rest and in use according to your threat model.

CUSTOMER_KEY_PKCS11_NAME

Optional, mandatory if CUSTOMER_KEY_FILE_PEM is not set

The keypair alias for a PKCS11 keypair, typically stored on a Hardware Security Module (HSM) and provided through a helper tool. This is expected to act in place of the RSA 2048-bit Private key specified with CUSTOMER_KEY_FILE_PEM, and will be used as the signing device for all future pre-boot authentication images.

The value should take the format:

"pkcs11:object=<keypair-alias>;type=private"

Warning

You must use double quotes to enclose the value.

Warning

The PKCS11 provider, and it’s associated HSM, should be considered key material and should be protected while at rest and in use according to your threat model.

GOLD_MASTER_OS_FILE

Mandatory

This should be your 'gold master' OS image. No customisation should be present in this image that you would not expect to be deployed to your entire fleet. rpi-sb-provisioner assumes this image has been created using pi-gen, and using a non-pi-gen image may produce undefined behaviour.

RPI_DEVICE_STORAGE_TYPE

Mandatory

Specify the kind of storage your target will use. Supported values are sd, emmc, nvme.

RPI_DEVICE_FAMILY

Mandatory

Specify the family of Raspberry Pi device you are provisioning. Supported values are 4, 5. For example,

A Raspberry Pi Compute Module 4 would be family 4 A Raspberry Pi 5 would be family 5

RPI_DEVICE_BOOTLOADER_CONFIG_FILE

Mandatory, with a default

Warning

rpi-sb-provisioner will ignore the Raspberry Pi Bootloader configuration built by pi-gen, and use the one provided in this variable.

Specify the Raspberry Pi Bootloader configuration you want your provisioned devices to use. A default is provided.

Further information on the format of this configuration file can be found in the Raspberry Pi Documentation, at https://www.raspberrypi.com/documentation/computers/config_txt.html

RPI_DEVICE_LOCK_JTAG

Optional

Raspberry Pi devices have a mechanism to restrict JTAG access to the device.

Note that using this function will prevent Raspberry Pi engineers from being able to assist in debugging your device, should you request assitance.

Set to any value to enable the JTAG restrictions.

RPI_DEVICE_EEPROM_WP_SET

Optional

Raspberry Pi devices that use an EEPROM as part of their boot flow can configure that EEPROM to enable write protection - preventing modification.

Set to any value to enable EEPROM write protection.

RPI_DEVICE_FETCH_METADATA

Optional

Collect manufacturing data from each device that is provisioned. This will include the board type, board revision number, the processor name, the memory configuration, and the factory where the board was made.

The metadata is inserted into the log for the device, and also as a serial-number named JSON file under the metadata subdirectory of the device provisioning logs.

Set to any value to enable metadata collection.

RPI_SB_WORKDIR

Optional

Warning

If you do not set this variable, your modified OS intermediates will not be stored, and will be unavailable for inspection.

Set to a location to cache OS assets between provisioning sessions. Recommended for use in production. For example:

RPI_SB_WORKDIR=/srv/rpi-sb-provisioner/

DEMO_MODE_ONLY

Optional

Set to 1 to allow the service to run without actually writing keys or OS images. You may, for example, use DEMO_MODE_ONLY in combination with RPI_SB_WORKDIR to inspect the modifications rpi-sb-provisioner would make to your OS ahead of deployment.

Using rpi-sb-provisioner

rpi-sb-provisioner is composed of three systemd services that are triggered by the connection of a device in RPIBoot mode to a USB port. With rpi-sb-provisioner configured to your requirements, all that is therefore required is to connect your target Raspberry Pi device in RPIBoot mode.

For Raspberry Pi Compute Module 4 on Raspberry Pi Compute Module 4 IO Board, you can do this by using the single jumper wire to connect the disable eMMC Boot pins on the 12-pin header at the top of the board

Figure 4. Force your Compute Module into RPIBoot mode by connecting the 'disable eMMC Boot' pins

After connecting your device in RPIBoot mode, rpi-sb-provisioner will perform the following steps:

• A new device connection is recognised over USB, and enters the triage phase:

  • If your device has not been recorded as having been provisioned, start the provisioner

  • If the device has been recorded as having been provisioned, cease further actions

• In the provisioner phase:

  • Your device will boot a specialised Raspberry Pi firmware, designed to write a hash of your public signing key (generated from the file pointed to by CUSTOMER_KEY_FILE_PEM) into device One Time Programmable (OTP) memory

  • Your device will be updated to Raspberry Pi EEPROM software released on 2024-05-17

  • Your device will perform a silent reboot

  • rpi-sb-provisioner will boot your device with a specialised Linux distribution designed to:

    • create a device unique key

    • partition and format your device’s storage

    • create a LUKSv2 container

    • place your OS into the LUKSv2 container

    • place a customised pre-boot authentication firmware (derived from your gold master OS image) into the 'boot' partition of your device’s storage

After these steps have been completed, your device should display both the activity and power LEDs as off. If you have ethernet connected, you may still see activity from this port. In this state, your device is safe to power off and package into your product.

No further intervention is required in the success case.

Warning

rpi-sb-provisioner will not, by default, block JTAG access. If you wish to make use of this facility, you must specify this in the Raspberry Pi Bootloader configuration pointed to by RPI_DEVICE_BOOTLOADER_CONFIG_FILE

Monitoring via the monitoring application

Warning

`rpi-sb-provisioner' must be installed with `--install-suggests' for `monitor.sh' to work. This will require installation of `python3-textual' and `python3-rich' from Debian’s Trixie release.

rpi-sb-provisioner also contains a monitoring application. This can be used to observe the progress of a device as it is being provisioned. It also allows for easy introspection of the log files and lists all completed and failed devices. The monitoring application supports both mouse or keyboard input. Navigation between boxes can be acheived by using the tab key or by clicking on the desired area.

To run, type into a terminal window:

$ monitor.sh

The TUI will intialise with 2 rows, the top one showing the progress of a device throughout the process, with each of the columns being for devices in the following stages: triaging and provisoning. When a device is connected, you will be able to watch it progress through each of the sections. The second row of the TUI also has two boxes at the bottom, the left being successfully completed provisions and the right for failed provisions. Clicking on the device name will open up a second window, with buttons to view the log files for each step of the provisioning service. To return to the main monitoring screen, just press the key m. To quit the app use the key combination CTRL-C or q.

Debugging and audit

Observing active provisioning operations

As rpi-sb-provisioner is implemented using systemd services, you can use the typical systemctl commands to observe the services as they provision your device.

To see active provisioning operations, and the serial numbers of the devices involved, type into a Terminal window:

$ systemctl list-units rpi-sb-provisioner*

Observing logs

Logs are stored on a per-device, per-phase basis, where logs for a given device are stored at /var/log/rpi-sb-provisioner/<serial>/<phase>.log.

For example, to observe the progress of an individual device through a phase, you could use tail:

$ tail -f -n 100 /var/log/rpi-sb-provisioner/<serial>/provisioner.log
$ tail -f -n 100 /var/log/rpi-sb-provisioner/<serial>/triage.log

Identifying secured devices

A 'secured device' is one where your customer signing key has been written - regardless of the state of your OS or other software. Such devices can only load Linux images signed by your customer signing key.

Obtain this by inspecting the rpi-sb-provisioner logs:

grep -R /var/log/rpi-sb-provisioner/ --include="progress" -e "PROVISIONER-FINISHED" | tail -n 1 | cut -d '/' -f 5

Inspecting the image to be flashed

When run with DEMO_MODE_ONLY=1, rpi-sb-provisioner will only prepare images to be provisioned - allowing you to inspect the OS images prior to mass deployment.

Warning

You must set RPI_SB_WORKDIR in the configuration file to observe the modified image. If you do not set RPI_SB_WORKDIR, the intermediates will be deleted at the completion of the run.

With both variables set, connect a device to be demo-provisioned per the provisoning instructions above.

The images will be located in the directory pointed to by RPI_SB_WORKDIR.

Warning

Remember to unset DEMO_MODE_ONLY before moving to mass deployment.

Debugging unexpected results

The first stage of debugging unexpected results is to delete the contents of the directory pointed to by RPI_SB_WORKDIR, which will force any intermediate OS images to be deleted.

$ sudo rm ${RPI_SB_WORKDIR}/*

The second stage is to remove the progress file matching the serial number of the device you are debugging:

$ sudo rm /var/log/rpi-sb-provisioner/<serial>/progress

Temporarily disabling rpi-sb-provisioner

You can disable rpi-sb-provisioner for using rpiboot in other scripts or tools by disabling the udev rule that activates rpi-sb-provisioner:

$ sudo ln -s /dev/null /etc/udev/rules.d/60-rpi-sb-provisioner.rules

To re-enable the trigger, remove the override file:

$ sudo rm /etc/udev/rules.d/60-rpi-sb-provisioner.rules