Enable LUKS2 and Argon2 Support for Packages

Aug 21, 2022 Updated: Jan 3, 2023 4 minutes to read

Because the LUKS partition uses LUKS2 and Argon2id, support for these LUKS configurations must be enabled for all software packages that unlock the LUKS partition.

Set USE Flags

The following USE settings need to be added to /etc/portage/package.use:

sys-apps/systemd cryptsetup
sys-boot/grub device-mapper
sys-fs/cryptsetup argon2 -static-libs

The detailed instructions to do this are available in the Handbook.

The USE flag settings for sys-fs/cryptsetup above should not change anything as they are the same as the package’s default USE flag settings, so they do not need to be explicitly declared; rather, they are included for completeness. The argon2 USE flag must be enabled for Argon2id support. The static-libs USE flag must be disabled so cryptsetup can be built into the initramfs by dracut, or else the LUKS partition could not be unlocked during boot.

Add Patches for GRUB 2.06

GRUB 2.06 has limited support for LUKS2. Although code implementing partial LUKS2 support exists in this version, the bootloader files installed using the default procedure do not support LUKS2. Argon2id is not supported at all in this version either.

Luckily, after applying the following patches to GRUB 2.06, LUKS2 support can be added to the installed bootloader files automatically, and Argon2id is supported too.

4500-grub-2.06-runtime-memregion-alloc.patch: A patch set that allows GRUB to allocate new consecutive and large memory chunks, which is a prerequisite for Argon2 support in GRUB. Argon2 enhances the security of LUKS by increasing the size of memory required for unlocking computations, so GRUB must be able to allocate more memory when needed. This patch set was cherry-picked from changes staged for the next GRUB release.
5000-grub-2.06-luks2-argon2-v4.patch: The patch set that adds Argon2 support itself to GRUB. It was submitted to the grub-devel mailing list, but the GRUB project’s maintainers have not responded with regards to it yet.
9500-grub-AUR-improved-luks2.patch: A patch included in the grub-improved-luks2-git package on the AUR, which is what the Arch Wiki’s GRUB article recommends for users seeking great LUKS2 support in GRUB. This patch allows the grub-install command to automatically install bootloader files with LUKS2 support.

The numbers in front of the patches’ file names are there only to control the order in which they are applied (patches with a smaller ordinal are applied first). As long as the order is maintained, these numbers’ values are arbitrary.

To apply these patches to Gentoo’s GRUB package – sys-boot/grub, add them as Portage user patches to /etc/portage/patches/sys-boot/grub-2.06. Patches at this location are applied to all Gentoo revisions of GRUB 2.06 (-r3, -r4, etc.). The following commands may be used to do this:

# mkdir -p /etc/portage/patches/sys-boot/grub-2.06
# cd /etc/portage/patches/sys-boot/grub-2.06
# curl -O https://leo3418.github.io/res/collections/gentoo-config-luks2-grub-systemd/4500-grub-2.06-runtime-memregion-alloc.patch
# curl -O https://leo3418.github.io/res/collections/gentoo-config-luks2-grub-systemd/5000-grub-2.06-luks2-argon2-v4.patch
# curl -O https://leo3418.github.io/res/collections/gentoo-config-luks2-grub-systemd/9500-grub-AUR-improved-luks2.patch

Readers who are interested in learning more about Portage’s user patch feature are welcome to read another article on this website that discusses it in depth.

Because the patch set for Argon2 support modifies the file grub-core/Makefile.core.def, according to the sys-boot/grub ebuild, the GRUB_AUTOGEN environment variable must be set. Otherwise, any builds of the package with the patch set applied would fail. The environment variable can be set exclusively for all Gentoo revisions of sys-boot/grub-2.06 in file /etc/portage/env/sys-boot/grub-2.06:

# mkdir -p /etc/portage/env/sys-boot
# echo 'GRUB_AUTOGEN=1' >> /etc/portage/env/sys-boot/grub-2.06

New Installation Only: Initialize Portage

If a new Gentoo installation is being performed, then please follow the instructions in the following Handbook sections under the Configuring Portage chapter:

Rebuild Packages

First, build sys-boot/grub with the patches applied. Before starting the build, please make sure that in the output of emerge, GRUB_PLATFORMS="efi-64" is enabled for sys-boot/grub. In other words, please check that efi-64 is listed without a minus sign (-) in front of it under GRUB_PLATFORMS. If this is not true, the Handbook has related instructions to fix it.

# emerge --ask --verbose sys-boot/grub

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N     ] sys-boot/grub-2.06-r2:2/2.06-r2::gentoo  USE="device-mapper fon
ts nls themes -doc -efiemu -libzfs -mount -sdl (-test) -truetype" GRUB_PLATFORMS
="efi-64 pc -coreboot -efi-32 -emu -ieee1275 (-loongson) -multiboot -qemu (-qemu
-mips) -uboot -xen -xen-32 -xen-pvh" 8171 KiB

Total: 1 package (1 new), Size of downloads: 8171 KiB

Would you like to merge these packages? [Yes/No]

Next, update the system’s world set to apply the USE flag changes:

# emerge --ask --verbose --update --deep --newuse @world