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Raspberry Pi 4 - secure boot

This directory contains the beta bootcode4.bin (recovery.bin) and pieeprom-2021-05-19.bin bootloader release. Older bootloader and recovery.bin releases do not support secure boot.

Steps for enabling secure boot:

Extra steps for Raspberry Pi 4B & Pi 400

Raspberry Pi 4B and Pi400 do not have a dedicated RPIBOOT jumper so a different GPIO must be used to enable RPIBOOT if pulled low. The available GPIOs are 2,4,5,6,7,8 since these are high by default.

Step 1 - Erase the EEPROM

In order to avoid this OTP configuration being accidentally set on Pi 4B / Pi 400 this option can only be set via RPIBOOT. To force RPIBOOT on a Pi 4B / Pi 400 erase the SPI EEPROM.

Copy recovery.bin to a blank FAT32 formatted SD card with the following config.txt file. Then insert the SD card and boot the Pi and wait at least 10 seconds for the green LED to flash rapidly.

erase_eeprom=1

Step 2 - Select the nRPIBOOT GPIO

Then use rpiboot config.txt specify the GPIO to use for nRPIBOOT. For example:

program_rpiboot_gpio=8

The OTP setting for nRPIBOOT will then be set in the next steps when the EEPROM / secure-boot configuration is programmed.

Optional. Specify the private key file in an environment variable.

Alternatively, specify the path when invoking the helper scripts.

export KEY_FILE="${HOME}/private.pem"

Optional. Customize the EEPROM config.

Custom with the desired bootloader settings. See: Bootloader configuration

Setting SIGNED_BOOT=1 enables signed-boot mode so that the bootloader will only boot.img files signed with the specified RSA key. Since this is an EEPROM config option secure-boot can be tested and reverted via RPIBOOT at this stage.

Generate the signed bootloader image

cd secure-boot-recovery
../tools/update-pieeprom.sh -k "${KEY_FILE}"

pieeprom.bin can then be flashed to the bootloader EEPROM via rpiboot.

Program the EEPROM image using rpiboot

  • Power off CM4
  • Set nRPIBOOT jumper and remove EEPROM WP protection
cd secure-boot-recovery
../rpiboot -d .
  • Power ON CM4

Locking secure-boot mode

After verifying that the signed OS image boots successfully the system can be locked into secure-boot mode. This writes the hash of the customer public key to "one time programmable" (OTP) bits. From then onwards:

  • The bootloader will only load OS images signed with the customer private key.
  • The EEPROM configuration file must be signed with the customer private key.
  • It is not possible to downgrade to an old version of the bootloader that doesn't support secure boot.
  • This option requires EEPROM version 2022-01-06 or newer.
  • BETA bootloader releases are not signed with the ROM secure boot key and will not boot on a system where revoke_devkey has been set.

WARNING: Modifications to OTP are irreversible. Once revoke_devkey has been set it is not possible to unlock secure-boot mode or use a different private key.

To enable this edit the config.txt file in this directory and set program_pubkey=1

  • program_pubkey - If 1, write the hash of the customer's public key to OTP.
  • revoke_devkey - If 1, revoke the ROM bootloader development key which requires secure-boot mode and prevents downgrades to bootloader versions that don't support secure boot.

Disabling VideoCore JTAG

VideoCore JTAG may be permentantly disabled by setting program_jtag_lock in config.txt. This option has no effect unless revoke_revkey=1 is set and the EEPROM and customer OTP key were programmed successfully.

See config.txt