Using Secure Boot

This guide offers a step-by-step walkthrough for enabling the secure boot function on SP7350 platforms. Secure boot ensures that an SP7350 device boots exclusively with authorized software, protecting the boot process from malicious threats. Additionally, the SP7350 guarantees that only encrypted images are executed, preventing unauthorized access and potential security breaches.

Table of Contents

Flow of Secure Boot

The flow of secure boot is as follows:

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i-boot (ROM code):

1. At power-on, i-boot loads the x-boot image from an external boot device into SRAM.

2. It then verifies the digital signature of the image.

3. If the signature is correct, i-boot decrypts the x-boot image.

4. Upon successful decryption, it executes it.

x-boot:

1. x-boot begins by loading the DDR training firmware from an external boot device.

2. It then initializes the DDR controller and conducts training for the DDR PHY.

3. Once the DDR PHY training is successful, DDR DRAM becomes operational.

4. Next, x-boot loads the TF-A, OP-TEE, and U-Boot images from an external boot device into DRAM.

5. It verifies the secure hash value of these images.

6. If the verification succeeds, x-boot decrypts the images.

7. Upon successful decryption, executes TF-A, which then initiates OP-TEE and subsequently executes U-Boot.

U-Boot:

1. U-Boot loads the Linux kernel image from an external boot device into DRAM.

2. it then verifies its secure hash value.

3. If the verification is successful, U-Boot executes the Linux kernel image.

Compiling Code for Secure Boot

Download Sources of SP7350

Please refer to: https://sunplus.atlassian.net/wiki/spaces/C3/pages/1988034774

for downloading the sources, setting up the compilation environment for SP7350 platforms.

Configure the Building Environment

Navigate to the top folder of your Q654 (SP7350) project. Run the following command to initiate the configuration menu:

make config

Upon executing this command, a configuration menu will appear, providing several options for customization:

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In the configuration menu:

1. Choose the board you want to build the image for. For instance, press '2' to select "SP7350 IO Board."

2. Choose the boot device. For example, press '2' to specify booting from the SD card.

3. Choose root file-system of Linux. For example, press '7' to opt for “Ubuntu MATE MATE 24.04.1” as root file-system.

4. Choose boot modes. Press ‘2' to select building “Secure boot” images.

Once you have completed the configuration selections, the system will start configuring the building environment. This process may take a few seconds to a few minutes, depending on your computer's performance. Please wait patiently for the configuration to complete.

Please note that the system takes additional time to complete its initial run during the configuration process, as it requires the download of the toolchain.

Build Code

After completing all configurations, you are ready to initiate the code build. Execute the following command to commence the build process:

make

This will compile the code based on your chosen configurations. The duration of this process depends on your computer's performance, typically taking a few minutes. Kindly exercise patience and allow the system to complete the build.

After make command completes, it will display information similar to the following screenshot:

Save Your Secure Keys

After compilation completes, secure keys will be built. The make command creates new secure keys automatically when there are no secure keys in the default directories. Refer to the contents of the directory 'build/tools/secure_sp7350/secure' under the project top directory:

The device key is stored in the ‘otp_Device_keys/’ directory, and the secure-boot key is stored in the ‘otp_Sb_keys/’ directory. Remember to securely save the entire ‘otp_Device_keys’ and 'otp_Sb_keys' directories.

WARNING: If the keys are lost, you will never be able to create the same secure keys again. Your SP7350 chips with the old keys will become unusable.

Burn Secure Keys into OTP memory of SP7350 Chips

First, refer to https://sunplus.atlassian.net/wiki/x/Z4GAdg for burning bits in OTP.

To activate secure-boot of SP7350 chips, it is necessary to write secure keys into the OTP (One-Time Programmable) memory of the SP7350 chips. There are two keys defined in the OTP

• Secure boot key: The secure-boot key is for digital signatures.

• Device key: The device key is for decryption.

Each key is 32 bytes long.

Burn Secure-boot Public Key (for digital signature) into OTP Bit 512 ~ 765

The secure-boot key is stored in the file 'build/tools/secure_sp7350/secure/otp_Sb_keys/ed_pub_0.hex', For example, the contents of ed_pub_0.hex is:

Convert the key to little-endian 4-byte words:

Input it to OTP words one by one. Afterward, check and then press "Write."

The status window of the OTPTool indicates "WRITE Start..…” and then “WRITE Success!" as shown above.

Press 'Read' to read back content of OTP.

The status window of the OTPTool indicates "READ Start..…” and then “READ Success!" as shown above.

Burn Device Private Key (for decryption) into OTP Bit 768 ~ 1023

The device private key is stored in hex file ‘build/tools/secure_sp7350/secure/otp_Device_keys/x_priv_0.hex’. For example, the contents of x_priv_0.hex is:

Convert the key to little-endian 4-byte word:

Input it to OTP words one by one. Afterward, check and press "Write."

The status window of the OTPTool indicates "WRITE Start..…” and then “WRITE Success!" as shown above.

Press 'Read' to confirm the content of OTP.

The status window of the OTPTool indicates "READ Start..…” and then “READ Success!" as shown above.

Enable Secure Mode of SP7350 (Write 1 into OTP bit 0)

Modify bit 0 to 1 and then press "Write."

The status window of the OTPTool indicates "READ Start..…” and then “READ Success!" as shown above.

Enable MP Bit of SP7350 (Write 1 into OTP bit 2)

To safeguard keys from being accessed by end-users, enabling the MP bit prevents the CPU from reading keys.

Note that the MP bit can only be enabled on version B or later chips; otherwise, it will render the chips unusable.

Modify bit 2 to 1 and then press "Write."

Important Notes:

• Do not enable the MP bit for version A chips.

• Burning OTP bits is irreversible, and incorrect burns may render the chips unusable.

• Remember to save the keys in directories: otp_Sb_keys, and otp_Device_keys

Secure Boot

After burning the keys and enabling secure mode, the SP7350 is ready to boot in secure mode. Copy your secure image to an SD card, insert it into your SP7350 platform, and turn on the power to boot the platform.

Note that once the SP7350 is in secure mode, it will not boot a non-secure image or an image with an incorrect digital signature.

Log of Secure Boot from SD Card

Line 1: Displays the i-boot version.

Line 4: Indicates that the SP7350 is in secure mode.

Line 5: Shows that the SP7350 is booting from an SD card.

Line 39: Shows size of the x-boot image.

Line 46: Checksum of the x-boot image is successfully verified.

Line 55: Confirms that the digital signature of the x-boot image is successfully verified.

Line 63: Indicates successful decryption of the x-boot image.

Line 67: Displays the x-boot version.

Line 146: Indicates successful completion of DDR training.

Line 158: Confirms successful verification of the U-Boot image's hash value.

Line 159: Confirms successful verification of the fip image's hash value, which includes TF-A and OP-TEE images.

Line 166: Displays the TF-A (BL31) version.

Line 175: Displays the OP-TEE version.

Line 183: Displays the U-Boot version.

Line 231: Confirms successful verification of the Linux kernel image's hash value.

Line 239: Indicates that Linux is starting.

Line 242: Displays the Linux version.

Line 569: Linux kernel completes its initialization and begins executing the /sbin/init process..

Line 574: Displays the Ubuntu version.