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Tools to manage the Chrome OS bootloader

Project description

This project is a collection of tools that ease and automate interacting with depthcharge, the Chrome OS bootloader.

Depthcharge is built into the firmware of Chrome OS boards, uses a custom verified boot flow and usually cannot boot other operating systems as is. This means someone who wants to use e.g. Debian on these boards need to either replace the firmware or work their system into the format depthcharge expects. These tools are about the latter.

Right now these are developed on and tested with only one arm64 board, but everything will attempt to work on other boards based on my best guesses. Support for x86 boards is very limited at a fundamental level due to a lack of understanding on my part.

mkdepthcharge

The mkdepthcharge tool is intended to wrap mkimage and vbutil_kernel to provide reasonable defaults to them, hide their idiosyncrasies and automate creating a depthcharge-bootable partition image appropriate for the running architecture. An example invocation on a Samsung Chromebook Plus (v1, arm64) could be:

$ mkdepthcharge -o depthcharge.img --compress lzma \
    --cmdline "console=tty1 root=/dev/mmcblk0p2 rootwait" \
    /boot/vmlinuz.gz /boot/initrd.img rk3399-gru-kevin.dtb

Here, mkdepthcharge would automatically extract and recompress the kernel, create a FIT image, put command line parameters into a file, create an empty bootloader, and provide defaults for vboot keys and other arguments while building the partition image.

depthchargectl

The depthchargectl tool goes a step further and aims to fully automate bootable image creation and Chrome OS kernel partition management, even the board-specific and distro-specific parts. With proper integration with your distribution, depthchargectl can keep your system bootable across kernel and initramfs changes without any interaction on your part. Even without such integration, a single command automates most of the work:

# Use --allow-current if you only have one Chrome OS kernel partition.
$ sudo depthchargectl write --allow-current
Building depthcharge image for board 'Samsung Chromebook Plus' ('kevin').
Built depthcharge image for kernel version '5.10.0-6-arm64'.
Wrote image '/boot/depthcharge/5.10.0-6-arm64.img' to partition '/dev/mmcblk1p1'.
Set partition '/dev/mmcblk1p1' as next to boot.

# After a reboot, you or an init service should run this.
$ sudo depthchargectl bless
Set partition '/dev/mmcblk1p1' as successfully booted.

Installation

These tools depend on mkimage, vbutil_kernel, cgpt, and other utilities (util-linux, coreutils, etc.) that are usually installed by default on most Linux systems, so you need to install those first. You also need docutils to build the manual pages with rst2man, but only for that.

This project (or at least depthchargectl) is meant to be integrated into your operating system by its maintainers, and the best way to install it is through your OS’ package manager whenever possible.

Configuration

You can configure depthcharge-tools with the /etc/depthcharge-tools/config file, or by putting similar fragments in the /etc/depthcharge-tools/config.d directory. See the config.ini file for the built-in default configuration.

Settings in the [depthcharge-tools] section are the global defaults from which all commands inherit. Other than that, config sections have inheritence based on their names i.e. those in the form of [a/b/c] inherit from [a/b] which also inherits from [a]. Each subcommand reads its config from such a subsection.

Currently the following configuration options are available:

[depthcharge-tools]
enable-system-hooks: Write/remove images on kernel/initramfs changes
vboot-keyblock: The kernel keyblock file for verifying and signing images
vboot-private-key: The private key (.vbprivk) for signing images
vboot-public-key: The public key for (.vbpubk) verifying images

[depthchargectl]
board: Codename of a board to build and check images for
ignore-initramfs: Do not include an initramfs in the image
images-dir: Directory to store built images
kernel-cmdline: Kernel commandline parameters to use

For longer explanations check the manual pages of each command for options named the same as these.

Installation for development

If you want to use development versions, you can clone this repository and install using pip:

$ pip3 install --user -e /path/to/depthcharge-tools

Hopefully, you should be able to use depthchargectl with just that:

$ depthchargectl build --output depthcharge.img
Building depthcharge image for board 'Samsung Chromebook Plus' ('kevin').
Built depthcharge image for kernel version '5.10.0-6-arm64'.
depthchargectl.img

Most depthchargectl functionality needs root as it handles disks and partitions, and you need special care while invoking as root:

$ depthchargectl() {
    sudo PYTHONPATH=/path/to/depthcharge-tools \
        python3 -m depthcharge_tools.depthchargectl "$@"
}

$ depthchargectl list /dev/mmcblk0
S  P  T  PATH
1  2  0  /dev/mmcblk0p2
1  1  0  /dev/mmcblk0p4
0  0  15 /dev/mmcblk0p6

Contributing

I only own one chromebook, so I need your help to make it work with all others. Pull requests, bug reports, or even pointers in the right direction for existing issues are all welcome. Currently I need the most help with x86 boards.

License

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>

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