Kekboot

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Introduction

Kekboot is a bootloader designed to chainload other EFI files, like an OS, depending on the systems Wake up type.

Using Kekboot

How to build

  1. Clone the GNU EFI repository and follow the instructions the README.gnuefi.
  2. Test if one of the included GNU EFI apps is working
  3. Clone this repository into the apps directory
  4. Build the EFI application, like stated in the README.gnuefi, it’s inevitable to read the README.gnuefi!

How to Use

  1. Create a Data File

    Create a UTF-16 encoded file named myvar.data.
    It should contain 9 entries in the following format (all on one line):

    partitionGUID=filePath partitionGUID=filePath ...

    • partitionGUID: The GUID of the partition where the chainload EFI file is located.
    • filePath: The path to the EFI file on that partition.
    • The position of entries determines the WakeUpType.
      Position WakeUpType
      0 Reserved
      1 Other
      2 Unknown
      3 APM TIMER
      4 Modem Ring
      5 LAN Remote
      6 Power Switch
      7 PCI PME#
      8 AC Power Restored

    💡 You can find the partitionGUID and filePath using the efibootmgr command.

    1. Write the EFI Variable
      Use the efivar command to write the variable:
      efivar --write --name=1be4df61-93ca-11d2-aa0d-00e098032b8c-WakeUpType --datafile=myvar.data

    2. Verify the Variable
      Check that the variable was written correctly:
      efivar --print --name=1be4df61-93ca-11d2-aa0d-00e098032b8c-WakeUpType

    3. Prepare the EFI Application
      Rename your built EFI application to: BOOTX64.EFI
      Then copy it to the EFI system partition.

    4. Reboot
      Restart your system and boot from the EFI partition.

How it works

Kekboot utilizes the SMBIOS (System Management BIOS) specification to retrieve the WakeUpType.
It does this by iterating through the SMBIOS tables provided by UEFI, searching for the System Information table (Type 1) and the Wake-up Type byte.

If found, the EFI application proceeds to read and parse the previously created EFI variable.

Finally, the EFI file corresponding to the Wake-up Type is located on the appropriate partition, loaded into main memory, and prepared for execution.