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NOTE: This guide pertains to x86 hosts, and does not cover supported CrOS/ARM chromebooks. For ARM targets, you should refer to u-boot documentation.

This page is useful for those who wish to use the GRUB GRUB payload directly. If you’re using SeaBIOS, the boot process will work similarly to traditional BIOS systems; refer to the SeaBIOS documentation on https://seabios.org/SeaBIOS

Linux is generally assumed, especially for Libreboot development, but Libreboot also works quite nicely with BSD systems.

Refer to the following pages:

• How to Prepare and Boot a USB Installer in libreboot Systems
• Modifying the GRUB Configuration in libreboot Systems
• How to Harden Your GRUB Configuration, for Security

Libreboot does not support switching VGA modes, when coreboot’s libgfxinit is used on Intel GPUs. Many distros will install GRUB, which Libreboot then finds and executes, if running SeaBIOS payload; if using GRUB, just the distro’s grub.cfg file is loaded instead, by Libreboot’s own GRUB in flash.

Libreboot GRUB boots in text mode or uses the coreboot framebuffer. Anyway, set GRUB_TERMINAL=console in GRUB and you should be fine. This avoids GRUB, the one provided by your distro, switching video modes.

In Debian for example (steps largely the same on other distros):

Edit /etc/default/grub as root, and uncomment or add the line:

GRUB_TERMINAL=console

Then still as root, do these commands:

export PATH="$PATH:/sbin"
update-grub

NOTE: update-grub is very much Debian-centric. Not all distros will have it. On Arch-based distros for instance, you might do:

grub-mkconfig -o /boot/grub/grub.cfg

Now your distro’s GRUB menu should work, when your distro’s GRUB bootloader is executed from Libreboot’s SeaBIOS payload.

Full encryption for basic LUKS2 (with PBKDF or argon2 key derivation) is supported in libreboot. Legacy LUKS1 is also supported. On most other systems, /boot must be unencrypted, but Libreboot supports use of the GRUB bootloader as a coreboot payload, directly in the boot flash.

GRUB has code in it that can be used to unlock LUKS1 and LUKS2 dm-crypt, using the cryptomount command. With this, you can boot with true full disk encryption, by encrypting /boot.

This is a boon for security, because it’s harder to tamper with, and you could potentially write-protect plus maybe provide a password in GRUB at boot time.

The easiest way to use it is like this: in Linux, set up your partitions like you would, but use LVM volume groups, with group name grubcrypt and either:

• / as volume name rootvol and /boot as volume name bootvol
• / as volume name rootvol and /boot exists within it (no bootvol)

If your distro then installs GRUB, and provides a grub.cfg file under /boot/grub (within the distro, on your SSD/HDD file system), it should work. Libreboot’s GRUB will automatically give you a passphrase prompt, where you type your passphrase and it unlocks the volume. Then it will find your LVMs and it’ll boot from that.

Otherwise, to manually unlock it, you drop to the GRUB shell with C and do:

cryptomount -a

Or on a specific device, e.g.

cryptomount (ahci0,1)

This is similar to cryptsetup luksOpen in Linux.

Libreboot GRUB merges the PHC argon2 implementation, so it has full support for LUKS2 installations in addition to LUKS1. Libreboot 20231021 and higher has argon2 support, but older releases only supported PBKDF2 which would make LUKS2 dysfunctional unless you swapped it to use PBKDF2 (not argon2) and/or downgraded to LUKS1.

With modern Libreboot, you can just use LUKS2 as-is, on most/all Linux distros. At the time of the Libreboot 20231021 release, the GRUB upstream (on gnu.org) did not have these argon2 patches in its source tree, but Libreboot merges and maintains them out of tree.

You should specifically use argon2id. Please ensure this, because some older LUKS2 setups defaulted to the weaker argon2i. This post by Matthew Garret contains information about that:

https://mjg59.dreamwidth.org/66429.html

NOTE: You should also read the instructions about about GRUB_TERMINAL.

Linux kernel has a feature to do actions to the system any time, even with it freezes, this is called a Magic SysRq keys. You can do these actions with Alt + Sysrq + Command. These are the actions:

• Alt + SysRq + B: Reboot the system
• Alt + SysRq + I: Send SIGKILL to every process except PID 1
• Alt + SysRq + O: Shut off the system

If some of them don’t work, you have to enable it in the kernel command line paramter. So append sysrq_always_enabled=1 to your GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub

You can also run # sysctl kernel.sysrq=1 to enable them.

This may also apply to CentOS or Redhat. Chroot guide can be found on fedora website

Libreboot’s default GRUB config sources fedora’s grub config grub.cfg (in /boot/grub2/grub.cfg), fedora by default makes use of the linux16 command, where it should be saying linux

Do this in fedora:

Open /etc/grub.d/10_linux

Set the sixteenbit variable to an empty string, then run:

grub2-mkconfig -o /boot/grub2/grub.cfg

With newer versions of fedora, scripts from grub package default to generating BLS instead of grub.cfg. To change that behaviour add following line to /etc/default/grub (or modify existing one if it already exists):

GRUB_ENABLE_BLSCFG=false

Then generate grub.cfg with:

grub2-mkconfig -o /boot/grub2/grub.cfg

Markdown file for this page: https://libreboot.org/docs/linux/index.md

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