Full disk encryption secure boot

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(Last edited by Blt on 4 Aug 2022.)

This guide is to explain step by step how to setup Alpine Linux with Full Disk Encryption using LUKS2, /boot & / together on the same partition, encrypted swap for hibernation on a nvme drive, with UEFI & Secure Boot. The goal of this guide is to follow the KISS principle, lvm can be added, another file system can be used, multiple partitions for /home; /var/log etc.. can also be added, if running everything in one partition is not meeting your requirements.

Sequence of Events

  • Installing packages
  • Partitioning the disk
  • Configuring LUKS
  • Mounting points and File System
  • Installing Alpine
  • mkinitfs settings & modules
  • Grub settings
  • Configuring Secure Boot

Installing packages

To facilitate the partitioning we will use gdisk : 

# apk add lsblk gptfdisk

For encryption, we will use cryptsetup : 

# apk add cryptsetup

For using and managing UEFI, multiple packages are needed : 

# apk add efibootmgr e2fsprogs grub grub-efi

Partitioning the disk

Let's assume the disk is /dev/nvme0n1 and no partition is present, we will create three partitions :

  • one for UEFI
  • one for /
  • one for swap (hibernation)
# gdisk /dev/nvme0n1
GPT fdisk (gdisk) version 1.0.9.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): d
No partitions

Command (? for help): n
Partition number (1-128, default 1): 
First sector (2048-1000215182, default = 2048) or {+-}size{KMGTP}: 
Last sector (2048-1000215182, default = 1000214527) or {+-}size{KMGTP}: 512M
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): ef00
Changed type of partition to 'EFI system partition'

Command (? for help): n
Partition number (2-128, default 2): 
First sector (1048577-1000215182, default = 1050624) or {+-}size{KMGTP}: 
Last sector (1050624-1000215182, default = 1000214527) or {+-}size{KMGTP}: 16G
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): 8200
Changed type of partition to 'Linux swap'

Command (? for help): n
Partition number (3-128, default 3): 
First sector (1048577-1000215182, default = 33556480) or {+-}size{KMGTP}: 
Last sector (33556480-1000215182, default = 1000214527) or {+-}size{KMGTP}: 
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): 8309
Changed type of partition to 'Linux LUKS'

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/nvme0n1.
The operation has completed successfully.

Configuring LUKS

# cryptsetup -v -c aes-xts-plain64 -s 512 --hash sha512 --pbkdf pbkdf2 --iter-time 5000 --use-random luksFormat /dev/nvme0n1p2

WARNING!
========
This will overwrite data on /dev/nvme0n1p2 irrevocably.

Are you sure? (Type 'yes' in capital letters): YES
Enter passphrase for /dev/nvme0n1p2: 
Verify passphrase: 
Key slot 0 created.
Command successful.

# cryptsetup -v -c aes-xts-plain64 -s 512 --hash sha512 --pbkdf pbkdf2 --iter-time 5000 --use-random luksFormat /dev/nvme0n1p3

WARNING!
========
This will overwrite data on /dev/nvme0n1p3 irrevocably.

Are you sure? (Type 'yes' in capital letters): YES
Enter passphrase for /dev/nvme0n1p3: 
Verify passphrase: 
Key slot 0 created.
Command successful.

Mounting points and File System

Open the LUKS partitiond we just created: 

# cryptsetup luksOpen /dev/nvme0n1p2 nvme0n1p2-crypt
# cryptsetup luksOpen /dev/nvme0n1p3 nvme0n1p3-crypt

Create vfat file system for UEFI partition: 

# mkfs.vfat /dev/nvme0n1p1

Create ext4 file system for swap partition: 

# mkfs.ext4 /dev/mapper/nvme0n1p2-crypt

Create ext4 file system for / partition: 

# mkfs.ext4 /dev/mapper/nvme0n1p3-crypt

Create mounting points and mount partitions : Mount / partition to /mnt : 

# mount -t ext4 /dev/mapper/nvme0n1p3-crypt /mnt

Create /boot/efi: 

# mkdir /mnt/boot/efi -p

Mount UEFI partition to /mnt/boot/efi : 

# mount -t vfat /dev/nvme0n1p1 /mnt/boot/efi

Activate SWAP: 

# mkswap /dev/mapper/nvme0n1p2-crypt
# swapon /dev/mapper/nvme0n1p2-crypt

Check partition scheme: 

# lsblk
NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
nvme0n1             259:0    0 476.9G  0 disk  
├─nvme0n1p1         259:1    0   511M  0 part  /mnt/boot/efi
├─nvme0n1p2         259:2    0  15.5G  0 part  
│ └─nvme0n1p2-crypt 253:0    0  15.5G  0 crypt [SWAP]
└─nvme0n1p3         259:3    0 460.9G  0 part  
  └─nvme0n1p3-crypt 253:1    0 460.9G  0 crypt /mnt

Installing Alpine

# setup-disk -m sys /mnt/

mkinitfs settings & modules

Edit the /mnt/etc/mkinitfs/mkinitfs.conf file and append the cryptsetup module to the features parameter (keymap only needed if QWERTY is not used): 

features="...keymap cryptsetup cryptkey"

Regenerate the initram: 

# mkinitfs -c /mnt/etc/mkinitfs/mkinitfs.conf -b /mnt/ $(ls /mnt/lib/modules/)

Grub settings

Create a crypto_keyfile.bin to avoid typing the passphrase twice during the boot process (one for Grub partition, one for Alpine partition): 

# touch /mnt/crypto_keyfile.bin
# chmod 600 /mnt/crypto_keyfile.bin
# dd bs=512 count=4 if=/dev/urandom of=/mnt/crypto_keyfile.bin
# cryptsetup luksAddKey /dev/nvme0n1p3 /mnt/crypto_keyfile.bin

Then, let's mount and chroot to our fresh installation: 

# mount -t proc /proc /mnt/proc
# mount --rbind /dev /mnt/dev
# mount --make-rslave /mnt/dev
# mount --rbind /sys /mnt/sys
# chroot /mnt

Let's show the UUID of our partition scheme: 

# lsblk -f

Edit /etc/default/grub and add a new line starting with GRUB_CMDLINE_LINUX parameter, replacing <UUID> with the UUID of the encrypted partition (in this case /dev/nvme0n1p3) and adding a new GRUB_PRELOAD_MODULES line like this: 

GRUB_CMDLINE_LINUX="cryptroot=UUID=<UUID> cryptdm=nvme0n1p3-crypt cryptkey"
GRUB_PRELOAD_MODULES="luks cryptodisk part_gpt"

Create a /root/grub-pre.cfg and replace <UUID_WITHOUT_HYPHENS> with your encrypted root partition UUID (here /dev/nvme0n1p3) without hyphens 

set crypto_uuid=<UUID_WITHOUT_HYPHENS>
cryptomount -u $crypto_uuid
set root=crypto0
set prefix=($root)/boot/grub
insmod normal
normal

Configuring Secure Boot

# apk add efi-mkkeys efibootmgr sbsigntool
# efi-mkkeys -s "Your Name" -o /etc/uefi-keys

Re-install Grub: 

# grub-mkimage -p /boot/grub -O x86_64-efi -c /root/grub-pre.cfg -o /tmp/grubx64.efi luks2 part_gpt cryptodisk ext2 gcry_rijndael pbkdf2 gcry_sha512
# install -v /tmp/grubx64.efi /boot/efi/EFI/AlpineLinuxSecureBoot/
# sed -i 's/SecureBoot/SecureB00t/' /boot/efi/EFI/AlpineLinuxSecureBoot/grubx64.efi
# cd /boot/efi/EFI/AlpineLinuxSecureBoot/
# sbsign --key /etc/uefi-keys/db.key --cert /etc/uefi-keys/db.crt --output grubx64.efi.signed grubx64.efi
# grub-mkconfig -o /boot/grub/grub.cfg
# efibootmgr --disk /dev/nvme0n1p1 --part 1 --create --label 'Alpine Linux Secure Boot Signed' --load /EFI/AlpineLinuxSecureBoot/grubx64.efi.signed --verbose

To check that your .efi is signed : 

 # sbverify --cert /etc/uefi-keys/db.crt /boot/efi/EFI/AlpineLinuxSecureBoot/grubx64.efi.signed 
Signature verification OK
sbverify --list /boot/efi/EFI/AlpineLinuxSecureBoot/grubx64.efi.signed
signature 1
image signature issuers:
 - /CN="Your Name" (db)
image signature certificates:
 - subject: /CN="Your Name" (db)
   issuer:  /CN="Your Name" (db)

Reboot

Import keys to UEFI

Copy db.auth, KEK.auth and PK.auth files from /etc/uefi-keys to a FAT formatted file system. This is just an example from an XPS laptop, each UEFI is unique.

  1. Go to Boot Configuration > Secure Boot
  2. Change Enable Secure Boot to ON
  3. Change Secure Boot Mode to Deployed Mode
  4. Change Enable Custom Mode to ON
  5. Go to Custom Mode Key Management
    • Reset All Keys
    • Select Key Database select db > Replace from file > select your Flash Drive > select db.auth
    • Select Key Database select KEK > Replace from file > select your Flash Drive > select KEK.auth
    • Select Key Database select PK > Replace from file > select your Flash Drive > select PK.auth
  6. APPLY CHANGES > EXIT

Check Secure Boot State: 

# apk add mokutil
# mokutil --sb-state
SecureBoot enabled

Congrats!

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