ownerboot

Ownerboot is a set of nix expressions which use nixpkgs to build bootloader images for owner-controlled computers.

All the necessary components (coreboot, kernel, busybox-based initramfs with cryptsetup/lvm2) are stored entirely in the bootloader flash chip. This leaves no writable unencrypted media in the boot process when the flash chip's write protect pin is shorted.

Ownerboot extends coreboot with a new normal/fallback mechanism. The flash chip holds two complete copies of the bootloader; only a single page (the bootblock) is shared between them. Each image can be flashed and write-protected indepedently of the other. The fallback image can be selected by /dev/watchdog, nvramtool, or physical input (front-panel button on servers, stylus eject on laptops).

Because ownerboot is written in nix, it can ensure that these builds are deterministic. Ownerboot contains no binaries, and instantiates nixpkgs with config.allowNonSource=false; if you disable nix's binary substituter you are assured that all the software in your bootloader will be built from source on your local machine, all the way back to the compiler which compiles your compiler.

Building

Copypasta:

git submodule init
git submodule update --depth 1 nixpkgs
export NIX_PATH=$(pwd)
nix build --option trusted-public-keys "" -L -f src kgpe.coreboot    # kgpe-d16 AMD opteron
nix build --option trusted-public-keys "" -L -f src am1i.coreboot    # am1-i AMD kabini
nix build --option trusted-public-keys "" -L -f src kevin.coreboot   # Samsung chromebook rk3399 arm64

Details: doc/build.md.

All that compiling and it just dumps me at a bash prompt?

Right now, yes.

On my own machines, I have a pile of big ugly bash scripts for /linuxrc (i.e. initramfs PID 1, which exec()s the long-lived PID 1). These are a complete mess and totally unsuitable for public release. I'm rewriting them in Rust and will publish the result of that work when it's ready.

Supported hardware

Current (all require a 16mbyte flash chip):

• KGPE-D16 motherboards (amd64): target kgpe
• AM1-I motherboards (amd64): target am1i
• Samsung XE513c24 "gru-kevin" Chromebook Plus (arm64): target kevin

Planned:

• Cavium Octeon routers (ER-4, ER-6, and ER-12), likely using u-boot "falcon mode"
• Raptor Computing Talos2 -- Arctic Tern required

Additional Tools

Ownerboot includes two nixpkgs-style packages:

• em100: a nix expression for the coreboot project's open-source driver for the em100 flash chip emulator.
• flashrom-wp: adds an out-of-tree patch to flashrom to configure which range of bytes are protected by the write-protect pin. Upstream does not have this feature. There appears to be adding some work towards adding it. Work on this began in 2016.

I'm not sure either of these really belongs in nixpkgs, but they are useful to the same kinds of people who might be interested in ownerboot. So this is a good place for them.

Code Overview

See doc/architecture.md.

Acknowledgements

• This project was originally inspired by the petitboot kexec-based bootloader, a derivative of which is shipped with Raptor Computing's POWER9 hardware.

• The independent write protection of normal/fallback images was inspired by a similar scheme used by the Embedded Controller firmware in arm64 Chromebooks.

• The nix language is, by far, the most advanced solution available for auditable and reproducible builds of complex software. An incredible amount of software goes into an ownerboot image (almost none of which was written by me!); it's effectively a tiny Linux distribution, and as a bootloader it is at the pinnacle of security sensitivity. Nothing else besides nix gave me any confidence that I knew what was going into my bootloader.

• nixpkgs was chosen because it is policy-free software: it doesn't force any policy decisions on its dependees. nixpkgs also has amazing support for cross-compilation; once you've used it you'll never want to deal with cross compilers any other way, ever again.

License

Everything in this repository is licensed under the GNU General Public License, version 2 or later (at your option).