Exercise - Feature Customization - Verified Boot

Note

In this exercise, we’ll learn how to enable and verify Verified Boot, it will demonstrate that boot stage signature verification will fail if a user modifies a byte in one of the stages

You can execute SBL with the following steps:

  1. Use HEX editor to modify one byte in the SBL image:

1.) Rebuild SBL by using the following command:

python BuildLoader.py build qemu

2.) Completion: you will see Done [qemu] on the screen after compile completed

3.) Check Flash Map on stage2 offset located at where (example here stage2 is located at 0x18000000)

Compile completed

4.) Open SlimBootloader.bin on <sbl_tree>\Outputs\qemu\

5.) Goto offset 0x18000000 and select one byte to modify it to 0x00, and save the image

Compile completed

6.) Example here updated offset 0x18000025 (Make sure to SAVE the changes!)


  1. Execute SBL on QEMU by using the following command
  • Windows:

    "C:\Program Files\qemu\qemu-system-x86_64.exe" -m 256M -machine q35 -serial stdio  -pflash Outputs\qemu\SlimBootloader.bin
    
  • Linux:

    qemu-system-x86_64 -m 256M -machine q35 -serial mon:stdio -nographic -pflash Outputs/qemu/SlimBootloader.bin
    
  1. Boot up failed on stage 1B

    Compile completed
  2. Modify board configuration file, CHANGE the line in file <sbl_tree>\Platform\QemuBoardPkg\BoardConfig.py

    self.HAVE_VERIFIED_BOOT = 0
    
    Compile completed

  1. Rebuild SBL by using the following command:

    python BuildLoader.py build qemu
    
  2. Completion: you will see Done [qemu] on the screen after compile completed

  3. Use HEX editor to modify one byte in the SlimBootloader image:

    1.) Open SlimBootloader.bin on <sbl_tree>\Outputs\qemu\

    2.) Goto offset 0x18000025 and modify it to 0x00, and SAVE the image

    3.) Execute SBL on QEMU by using the following command:

    • Windows:

      "C:\Program Files\qemu\qemu-system-x86_64.exe" -m 256M -machine q35 -serial stdio  -pflash Outputs\qemu\SlimBootloader.bin
      
    • Linux:

      qemu-system-x86_64 -m 256M -machine q35 -serial mon:stdio -nographic -pflash Outputs/qemu/SlimBootloader.bin
      
Compile completed

Tip

BoardConfig.py contains lots of options for customization. Most of the SBL static features and Flash image layout can be customized here.