Arch Linux Full-Disk Encryption Installation Guide [Encrypted Boot, UEFI, NVMe, Evil Maid]

full-disk-encryption-arch-uefi.md

Arch Linux Full-Disk Encryption Installation Guide

This guide provides instructions for an Arch Linux installation featuring full-disk encryption via LVM on LUKS and an encrypted boot partition (GRUB) for UEFI systems.

Following the main installation are further instructions to harden against Evil Maid attacks via UEFI Secure Boot custom key enrollment and self-signed kernel and bootloader.

Preface

You will find most of this information pulled from the Arch Wiki and other resources linked thereof.

Note: The system was installed on an NVMe SSD, substitute /dev/nvme0nX with /dev/sdX or your device as needed.

Pre-installation

Connect to the internet

Plug in your Ethernet and go, or for wireless consult the all-knowing Arch Wiki.

Update the system clock

timedatectl set-ntp true

Preparing the disk

Create EFI System and Linux LUKS partitions

Create a 1MiB BIOS boot partition at start just in case it is ever needed in the future

Number	Start (sector)	End (sector)	Size	Code	Name
1	2048	4095	1024.0 KiB	EF02	BIOS boot partition
2	4096	1130495	550.0 MiB	EF00	EFI System
3	1130496	976773134	465.2 GiB	8309	Linux LUKS

gdisk /dev/nvme0n1

o
n
[Enter]
0
+1M
ef02
n
[Enter]
[Enter]
+550M
ef00
n
[Enter]
[Enter]
[Enter]
8309
w

Create the LUKS1 encrypted container on the Linux LUKS partition (GRUB does not support LUKS2 as of May 2019)

cryptsetup luksFormat --type luks1 --use-random -S 1 -s 512 -h sha512 -i 5000 /dev/nvme0n1p3

Open the container (decrypt it and make available at /dev/mapper/cryptlvm)

cryptsetup open /dev/nvme0n1p3 cryptlvm

Preparing the logical volumes

Create physical volume on top of the opened LUKS container

pvcreate /dev/mapper/cryptlvm

Create the volume group and add physical volume to it

vgcreate vg /dev/mapper/cryptlvm

Create logical volumes on the volume group for swap, root, and home

lvcreate -L 8G vg -n swap
lvcreate -L 32G vg -n root
lvcreate -l 100%FREE vg -n home

The size of the swap and root partitions are a matter of personal preference.

Format filesystems on each logical volume

mkfs.ext4 /dev/vg/root
mkfs.ext4 /dev/vg/home
mkswap /dev/vg/swap

Mount filesystems

mount /dev/vg/root /mnt
mkdir /mnt/home
mount /dev/vg/home /mnt/home
swapon /dev/vg/swap

Preparing the EFI partition

Create FAT32 filesystem on the EFI system partition

mkfs.fat -F32 /dev/nvme0n1p2

Create mountpoint for EFI system partition at /efi for compatibility with grub-install and mount it

mkdir /mnt/efi
mount /dev/nvme0n1p2 /mnt/efi

Installation

Install necessary packages

pacstrap /mnt base linux linux-firmware mkinitcpio lvm2 vi dhcpcd wpa_supplicant

Configure the system

Generate an fstab file

genfstab -U /mnt >> /mnt/etc/fstab

(optional) Change relatime option to noatime

/mnt/etc/fstab

# /dev/mapper/vg-root
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx / ext4 rw,noatime 0 1

# /dev/mapper/vg-home
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx / ext4 rw,noatime 0 1

Reduces writes to disk when reading from a file, but may cause issues with programs that rely on file access time

Enter new system chroot

arch-chroot /mnt

At this point you should have the following partitions and logical volumes:

lsblk

NAME	MAJ:MIN	RM	SIZE	RO	TYPE	MOUNTPOINT
nvme0n1	259:0	0	465.8G	0	disk
├─nvme0n1p1	259:4	0	1M	0	part
├─nvme0n1p2	259:5	0	550M	0	part	/efi
├─nvme0n1p3	259:6	0	465.2G	0	part
..└─cryptlvm	254:0	0	465.2G	0	crypt
....├─vg-swap	254:1	0	8G	0	lvm	[SWAP]
....├─vg-root	254:2	0	32G	0	lvm	/
....└─vg-home	254:3	0	425.2G	0	lvm	/home

Time zone

Set the time zone

Replace America/Los_Angeles with your respective timezone found in /usr/share/zoneinfo

ln -sf /usr/share/zoneinfo/America/Los_Angeles /etc/localtime

Run hwclock to generate /etc/adjtime

Assumes hardware clock is set to UTC

hwclock --systohc

Localization

Uncomment en_US.UTF-8 UTF-8 in /etc/locale.gen and generate locale

locale-gen

Create locale.conf and set the LANG variable

/etc/locale.conf

LANG=en_US.UTF-8

Network configuration

Create the hostname file

/etc/hostname

myhostname

This is a unique name for identifying your machine on a network.

Add matching entries to hosts

/etc/hosts

127.0.0.1 localhost
::1 localhost
127.0.1.1 myhostname.localdomain myhostname

Initramfs

Add the keyboard, encrypt, and lvm2 hooks to /etc/mkinitcpio.conf

Note: ordering matters.

HOOKS=(base udev autodetect keyboard modconf block encrypt lvm2 filesystems fsck)

Recreate the initramfs image

mkinitcpio -p linux

Root password

Set the root password

passwd

Boot loader

Install GRUB

pacman -S grub

Configure GRUB to allow booting from /boot on a LUKS1 encrypted partition

/etc/default/grub

GRUB_ENABLE_CRYPTODISK=y

Set kernel parameter to unlock the LVM physical volume at boot using encrypt hook

UUID is the partition containing the LUKS container

blkid

/dev/nvme0n1p3: UUID="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" TYPE="crypto_LUKS" PARTLABEL="Linux LUKS" PARTUUID="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"

/etc/default/grub

GRUB_CMDLINE_LINUX="... cryptdevice=UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx:cryptlvm ..."

To enable TRIM support during boot, set the kernel parameter as

Read Discard/TRIM support for solid state drives (SSD) to know what you are doing.

/etc/default/grub

GRUB_CMDLINE_LINUX="... cryptdevice=UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx:cryptlvm:allow-discards ..."

Install GRUB to the mounted ESP for UEFI booting

pacman -S efibootmgr
grub-install --target=x86_64-efi --efi-directory=/efi

Enable microcode updates

grub-mkconfig will automatically detect microcode updates and configure appropriately

pacman -S intel-ucode

Use intel-ucode for Intel CPUs and amd-ucode for AMD CPUs.

Generate GRUB's configuration file

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

(recommended) Embed a keyfile in initramfs

This is done to avoid having to enter the encryption passphrase twice (once for GRUB, once for initramfs.)

Create a keyfile and add it as LUKS key

mkdir /root/secrets && chmod 700 /root/secrets
head -c 64 /dev/urandom > /root/secrets/crypto_keyfile.bin && chmod 600 /root/secrets/crypto_keyfile.bin
cryptsetup -v luksAddKey -i 1 /dev/nvme0n1p3 /root/secrets/crypto_keyfile.bin

Add the keyfile to the initramfs image

/etc/mkinitcpio.conf

FILES=(/root/secrets/crypto_keyfile.bin)

Recreate the initramfs image

mkinitcpio -p linux

Set kernel parameters to unlock the LUKS partition with the keyfile using encrypt hook

/etc/default/grub

GRUB_CMDLINE_LINUX="... cryptkey=rootfs:/root/secrets/crypto_keyfile.bin"

Regenerate GRUB's configuration file

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

Restrict /boot permissions

chmod 700 /boot

The installation is now complete. Exit the chroot and reboot.

exit
reboot

Post-installation

Your system should now be fully installed, bootable, and fully encrypted.

If you embedded the keyfile in the initramfs image, it should only require your encryption passphrase once to unlock to the system.

For the standard Arch Linux post-installation steps, RTFM.

(recommended) Hardening against Evil Maid attacks

With an encrypted boot partition, nobody can see or modify your kernel image or initramfs, but you would be still vulnerable to Evil Maid attacks.

One possible solution is to use UEFI Secure Boot. Get rid of preloaded Secure Boot keys (you really don't want to trust Microsoft and OEM), enroll your own Secure Boot keys and sign the GRUB boot loader with your keys. Evil Maid would be unable to boot modified boot loader (not signed by your keys) and the attack is prevented.

Creating keys

The following steps should be performed as the root user, with accompanying files stored in the /root directory.

Install efitools

pacman -S efitools

Create a GUID for owner identification

uuidgen --random > GUID.txt

Platform key

CN is a Common Name, which can be written as anything.

openssl req -newkey rsa:4096 -nodes -keyout PK.key -new -x509 -sha256 -days 3650 -subj "/CN=my Platform Key/" -out PK.crt
openssl x509 -outform DER -in PK.crt -out PK.cer
cert-to-efi-sig-list -g "$(< GUID.txt)" PK.crt PK.esl
sign-efi-sig-list -g "$(< GUID.txt)" -k PK.key -c PK.crt PK PK.esl PK.auth

Sign an empty file to allow removing Platform Key when in "User Mode"

sign-efi-sig-list -g "$(< GUID.txt)" -c PK.crt -k PK.key PK /dev/null rm_PK.auth

Key Exchange Key

openssl req -newkey rsa:4096 -nodes -keyout KEK.key -new -x509 -sha256 -days 3650 -subj "/CN=my Key Exchange Key/" -out KEK.crt
openssl x509 -outform DER -in KEK.crt -out KEK.cer
cert-to-efi-sig-list -g "$(< GUID.txt)" KEK.crt KEK.esl
sign-efi-sig-list -g "$(< GUID.txt)" -k PK.key -c PK.crt KEK KEK.esl KEK.auth

Signature Database key

openssl req -newkey rsa:4096 -nodes -keyout db.key -new -x509 -sha256 -days 3650 -subj "/CN=my Signature Database key/" -out db.crt
openssl x509 -outform DER -in db.crt -out db.cer
cert-to-efi-sig-list -g "$(< GUID.txt)" db.crt db.esl
sign-efi-sig-list -g "$(< GUID.txt)" -k KEK.key -c KEK.crt db db.esl db.auth

Signing bootloader and kernel

When Secure Boot is active (i.e. in "User Mode") you will only be able to launch signed binaries, so you need to sign your kernel and boot loader.

Install sbsigntools

pacman -S sbsigntools

sbsign --key db.key --cert db.crt --output /boot/vmlinuz-linux /boot/vmlinuz-linux
sbsign --key db.key --cert db.crt --output /efi/EFI/arch/grubx64.efi /efi/EFI/arch/grubx64.efi

Automatically sign bootloader and kernel on install and updates

It is necessary to sign GRUB with your UEFI Secure Boot keys every time the system is updated via pacman. This can be accomplished with a pacman hook.

Create the hooks directory

mkdir -p /etc/pacman.d/hooks

Create hooks for both the linux and grub packages

/etc/pacman.d/hooks/99-secureboot-linux.hook

[Trigger]
Operation = Install
Operation = Upgrade
Type = Package
Target = linux

[Action]
Description = Signing Kernel for SecureBoot
When = PostTransaction
Exec = /usr/bin/find /boot/ -maxdepth 1 -name 'vmlinuz-*' -exec /usr/bin/sh -c 'if ! /usr/bin/sbverify --list {} 2>/dev/null | /usr/bin/grep -q "signature certificates"; then /usr/bin/sbsign --key /root/db.key --cert /root/db.crt --output {} {}; fi' \ ;
Depends = sbsigntools
Depends = findutils
Depends = grep

/etc/pacman.d/hooks/98-secureboot-grub.hook

[Trigger]
Operation = Install
Operation = Upgrade
Type = Package
Target = grub

[Action]
Description = Signing GRUB for SecureBoot
When = PostTransaction
Exec = /usr/bin/find /efi/ -name 'grubx64*' -exec /usr/bin/sh -c 'if ! /usr/bin/sbverify --list {} 2>/dev/null | /usr/bin/grep -q "signature certificates"; then /usr/bin/sbsign --key /root/db.key --cert /root/db.crt --output {} {}; fi' \ ;
Depends = sbsigntools
Depends = findutils
Depends = grep

Enroll keys in firmware

Copy all *.cer, *.esl, *.auth to the EFI system partition

cp /root/*.cer /root/*.esl /root/*.auth /efi/

Boot into UEFI firmware setup utility (frequently but incorrectly referred to as "BIOS")

systemctl reboot --firmware

Firmwares have various different interfaces, see Replacing Keys Using Your Firmware's Setup Utility if the following instructions are unclear or unsuccessful.

Set OS Type to Windows UEFI mode

Find the Secure Boot options and set OS Type to Windows UEFI mode (yes, even if we're not on Windows.) This may be necessary for Secure Boot to function.

Clear preloaded Secure Boot keys

Using Key Management, clear all preloaded Secure Boot keys (Microsoft and OEM).

By clearing all Secure Boot keys, you will enter into Setup Mode (so you can enroll your own Secure Boot keys).

Set or append the new keys

The keys must be set in the following order:

db => KEK => PK

This is due to some systems exiting setup mode as soon as a PK is entered.

Do not load the factory defaults, instead navigate the available filesystems in search of the files previously copied to the EFI System partition.

Choose any of the formats. The firmware should prompt you to enter the type (Note: type names may differ slightly.)

*.cer is a Public Key Certificate
*.esl is a UEFI Secure Variable
*.auth is an Authenticated Variable

Certain firmware (such as my own) require you use the *.auth files. Try various ones until they work.

Set UEFI supervisor (administrator) password

You must also set your UEFI firmware supervisor (administrator) password in the Security settings, so nobody can simply boot into UEFI setup utility and turn off Secure Boot.

You should never use the same UEFI firmware supervisor password as your encryption password, because on some old laptops, the supervisor password could be recovered as plaintext from the EEPROM chip.

Exit and save changes

Once you've loaded all three keys and set your supervisor password, hit F10 to exit and save your changes.

If everything was done properly, your boot loader should appear on reboot.

Check if Secure Boot was enabled

od -An -t u1 /sys/firmware/efi/efivars/SecureBoot-XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

The characters denoted by XXXX differ from machine to machine. To help with this, you can use tab completion or list the EFI variables.

If Secure Boot is enabled, this command returns 1 as the final integer in a list of five, for example:

6 0 0 0 1

If Secure Boot was enabled and your UEFI supervisor password set, you may now consider yourself protected against Evil Maid attacks.