MrChromebox's coreboot

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MrChromebox's coreboot

Fimware Utility Script

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Issue tracker (non-script-related firmware issues)

The MrChromebox's coreboot is a coreboot fork maintained by one of the coreboot leaders , Matt DeVillier (MrChromebox) . The fork targets Chrome OS devices based on x86 architecture. ARM is not supported .

Firmware Utility Script

Warning
Even though the scripts are stored on GitHub, the blob files will be downloaded from the MrChromebox's website . In the case of firmware blobs, only md5 and sha1 checksum verification is implemented, but the checksums are also stored on the website, which breaks all security. In addition, the script downloads binary tools from the website without any verification and runs them as root. Therefore, there is no way to know if the blobs or tools have been compomised.

MrChromebox provides a script that automatically detects the motherboard, downloads the compiled coreboot as a blob, injects the VPD into that blob, disables write protection, and flashes it to the device. The script can be executed as follows:

user $git clone https://github.com/MrChromebox/scripts

user $cd scripts

root #./firmware-util.sh

The current state of the script running on various live images:

Distribution	Version	Date	Status	Notes
Gentoo LiveGUI USB Image	20240707T170407Z	2024-07-14	Borked	The kernel is not permissive enough.
Linux Mint Cinnamon Edition Live Image	21.3	2024-07-14	Works	Works out of the box.
Ubuntu Desktop Live Image	24.04 LTS	2024-07-14	Works	Requires curl to be installed.

Manual installation

Device list

This is a list of Chrome OS devices on which manual installation has been successfully performed. Feel free to add to the list!

Device	Motherboard	coreboot version	Owner(s)	Status	Notes
Lenovo IdeaPad Flex 5 13IML05 Chromebook	akemi	2405.0	Lars Hint	Works

Linux Mint environment

Warning
EFI users should be aware that if Linux Mint is installed on an external disk, the EFI partition type code of the internal disk must be changed from EF00 to another partition type (e.g. 8300), otherwise the installer will screw up the partition instead of creating a new one on the external disk.

Important
After writing a live Linux Mint image to a USB drive, the following error will occur when booting to the drive and the process will hang:

stdin: Invalid argument

This happens because Linux Mint checks if the GPT at the beginning of the disk matches the GPT at the end, which does not exist. After checking, Linux Mint writes GPT at the end and hangs. To fix the problem, just do a hard reset and it will work on the next boot.

To achieve a more reproducible environment, the compilation will be performed from a Linux Mint system (version 21.3).

Install crossgcc dev-dependencies:

root #apt-get install git g++ zlib1g-dev gnat

Install coreboot dev-dependencies:

root #apt-get install libssl-dev uuid-dev nasm imagemagick

Install menuconfig dev-dependencies:

root #apt-get install libncurses-dev

Install flashrom dev-dependencies:

root #apt-get install meson libpci-dev

Create a symlink to python:

root #ln -s /usr/bin/python3 /usr/bin/python

Compilation

Clone the repository:

user $git clone --recurse-submodules https://github.com/MrChromebox/coreboot

user $cd coreboot

Select a version (all versions can be seen by executing git branch --all):

user $git checkout remotes/origin/MrChromebox-2405

Compile the cross-compiler:

user $make crossgcc-i386 CPUS=$(nproc)

Detect the name of the motherboard:

root #dmidecode --string system-product-name

Starting with version 4.22.0, there is a script in the repository to simplify the build :

user $./build-uefi.sh <MOTHERBOARD_NAME_IN_LOWER_CASE>

To see the compiled binary file, run the command:

user $ls ../roms/*.rom

Important
The binary is not yet ready for flashing as it requires VPD to be injected.

VPD injection

BIOS region extraction

Compile the flashrom:

user $git clone https://github.com/flashrom/flashrom

user $cd flashrom

user $git switch --detach v1.5.1

user $meson setup builddir

user $meson compile -C builddir

user $cd builddir

Extract the BIOS region into a file:

Intel-based device

root #./flashrom -p internal --ifd -i bios -r /tmp/bios.bin

Non-Intel-based device

root #./flashrom -p internal -r /tmp/bios.bin

VPD extraction and injection

Compile the cbfstool:

user $git clone https://github.com/coreboot/coreboot

user $cd coreboot

user $git switch --detach 24.05

user $make -C util/cbfstool

Note
Cloning the original coreboot repository is optional, as cbfstool is also present in the MrChromebox's fork.

Extract the VPD from the BIOS region extracted earlier:

user $./util/cbfstool/cbfstool /tmp/bios.bin read -r RO_VPD -f /tmp/vpd.bin

Ensure that the VPD is present:

user $hexdump -C /tmp/vpd.bin

Inject the VPD into the firmware file:

user $./util/cbfstool/cbfstool <FIRMWARE FILE PATH> write -r RO_VPD -f /tmp/vpd.bin

Flashing the firmware

Warning
This step may result in hardware damage or data loss. Before proceeding, ensure that everything required for unbricking is in place.

Note
* flashrom can output some failure messages that can be safely ignored, so it is necessary to know the status code (the last echo command must be equal to zero).

• After rebooting, the screen will be black for a minute.

Intel-based device

root #./flashrom -p internal --ifd -i bios -N -w <FIRMWARE FILE PATH>

root #echo $?

Non-Intel-based device

root #./flashrom -p internal -N -w <FIRMWARE FILE PATH>

root #echo $?

Customization

Note
It is highly recommended to perform the customization only after ensuring that everything works with the default values.

Find the location of the configuration file:

user $find ./configs -name "config.<MOTHERBOARD_NAME_IN_LOWER_CASE>.uefi"

Copy the configuration file to the root directory of the coreboot repository:

user $cp <PATH_TO_CONFIGURATION_FILE> ./.config

The configuration file has the same structure as the kernel configuration file and can be edited via menuconfig:

user $make menuconfig

After editing the configuration, the original configuration file needs to be replaced:

user $make savedefconfig

user $mv ./defconfig <PATH_TO_CONFIGURATION_FILE>

After replacement, it is necessary to (re)build the firmware by (re)running the build-uefi.sh script.

Custom BIOS name

The name is defined through CONFIG_LOCALVERSION, which can be changed in the build-uefi.sh file to, for example, this:

CODE

echo "CONFIG_LOCALVERSION=\"coreboot-2405\"" >> .config

Decreasing the boot timeout

To decrease the menu prompt display time from two seconds to one second:

KCONFIG

Payload  --->
  [ ] Don't add a payload
  (1)  Set the timeout for boot menu prompt Search for <code>CONFIG_EDK2_BOOT_TIMEOUT</code> to find this item.

Larry the Cow as the splash screen image

Download the image to the root directory of the repository:

user $wget wiki.gentoo.org/images/3/3d/Larry_color.svg

And set the path via menuconfig:

KCONFIG

Payload  --->
  [ ] Don't add a payload
  (Larry_color.svg) edk2 Bootsplash path and filename Search for <code>CONFIG_EDK2_BOOTSPLASH_FILE</code> to find this item.

See also

• Coreboot — a free and open-source hardware initializing firmware which supports multiple boot ROM payloads.
• Chromebook — installing Gentoo on a Chromebook

External resources

• ArchLinux » Chrome OS devices/Custom firmware