Root on ZFS with native encryption

This guide aims to setup encrypted Alpine Linux on ZFS with a layout compatible with boot environments. Mirror and RAID-Z supported.

Except EFI system partition and boot pool /boot, everything is encrypted. Root pool is encrypted with ZFS native encryption and swap partition is encrypted with dm-crypt.

To do an unencrypted setup, simply omit -O keylocation -O keyformat when creating root pool.

Useful links

• OpenZFS Getting Started

Notes

UEFI is required. Supports single disk & multi-disk (stripe, mirror, RAID-Z) installation.

Existing data on target disk(s) will be destroyed.

Preparation

Setup live environment

Download the extended release from https://www.alpinelinux.org/downloads/, as only this version is shipped with ZFS kernel module. Alpine Linux can not load kernel module in live.

Run the following command to setup the live environment, use default none option when asked about disks.

setup-alpine

Settings given here will be copied to the target system later by setup-disk.

Install system utilities

Install and setupeudev (a port of systemd udev by gentoo) to get block device names.

apk update
apk add eudev sgdisk grub-efi zfs
modprobe zfs
setup-udev

Variables

In this step, we will set some variables to make our installation process easier.

DISK=/dev/disk/by-id/ata-HXY_120G_YS

Use unique disk path instead of /dev/sda to ensure the correct partition can be found by ZFS.

Other variables

TARGET_USERNAME='your username'
ENCRYPTION_PWD='your root pool encryption password, 8 characters min'
TARGET_USERPWD='user account password'

Create a mountpoint

MOUNTPOINT=`mktemp -d`

Create a unique suffix for the ZFS pools: this will prevent name conflict when importing pools on another Root on ZFS system.

poolUUID=$(dd if=/dev/urandom of=/dev/stdout bs=1 count=100 2>/dev/null |tr -dc 'a-z0-9' | cut -c-6)

Partitioning

For a single disk, UEFI installation, we need to create at lease 3 partitions: - EFI system partition - Boot pool partition - Root pool partition Since GRUB only partially support ZFS, many features needs to be disabled on the boot pool. By creating a separate root pool, we can then utilize the full potential of ZFS.

Clear the partition table on the target disk and create EFI, boot and root pool parititions:

sgdisk --zap-all $DISK
sgdisk -n1:0:+512M -t1:EF00 $DISK
sgdisk -n2:0:+2G $DISK        # boot pool
sgdisk -n3:0:0 $DISK          # root pool

If you want to use a multi-disk setup, such as mirror or RAID-Z, partition every target disk with the same commands above.

Optional: Swap partition

Swap support on ZFS is also problematic, therefore it is recommended to create a separate Swap partition if needed. This guide will cover the creation of a separate swap partition.(can not be used for hibernation since the encryption key is discarded when power off.)

If you want to use swap, reserve some space at the end of disk when creating root pool:

sgdisk -n3:0:-8G $DISK        # root pool, reserve 8GB for swap at the end of the disk
sgdisk -n4:0:0 $DISK          # swap partition

Create boot and root pool

As mentioned above, ZFS features need to be selectively enabled for GRUB. All available features are enabled when no feature@ is supplied.

Here we explicitly enable those GRUB can support.

zpool create \
  -o ashift=12 -d \
  -o feature@async_destroy=enabled \
  -o feature@bookmarks=enabled \
  -o feature@embedded_data=enabled \
  -o feature@empty_bpobj=enabled \
  -o feature@enabled_txg=enabled \
  -o feature@extensible_dataset=enabled \
  -o feature@filesystem_limits=enabled \
  -o feature@hole_birth=enabled \
  -o feature@large_blocks=enabled \
  -o feature@lz4_compress=enabled \
  -o feature@spacemap_histogram=enabled \
  -O acltype=posixacl -O canmount=off -O compression=lz4 \
  -O devices=off -O normalization=formD -O relatime=on -O xattr=sa \
  -O mountpoint=/boot -R $MOUNTPOINT \
  bpool_$poolUUID $DISK-part2

Nothing is stored directly under bpool and rpool, hence canmount=off. The respective mountpoint properties are more symbolic than practical.

For root pool all available features are enabled by default

echo $ENCRYPTION_PWD | zpool create \
  -o ashift=12 \
  -O encryption=aes-256-gcm \
  -O keylocation=prompt -O keyformat=passphrase \
  -O acltype=posixacl -O canmount=off -O compression=lz4 \
  -O dnodesize=auto -O normalization=formD -O relatime=on \
  -O xattr=sa -O mountpoint=/ -R $MOUNTPOINT \
  rpool_$poolUUID $DISK-part3

For multi-disk

For mirror:

zpool create \
  ... \
  bpool_$poolUUID mirror \
  /dev/disk/by-id/target_disk1-part2 \
  /dev/disk/by-id/target_disk2-part2
zpool create \
  ... \
  rpool_$poolUUID mirror \
  /dev/disk/by-id/target_disk1-part3 \
  /dev/disk/by-id/target_disk2-part3

For RAID-Z, replace mirror with raidz, raidz2 or raidz3.

Create system datasets

This layout is intended to separate root file system from persistent files.

zfs create -o canmount=off -o mountpoint=none rpool_$poolUUID/HOME
zfs create -o canmount=off -o mountpoint=none rpool_$poolUUID/ROOT
zfs create -o canmount=off -o mountpoint=none bpool_$poolUUID/BOOT
zfs create -o mountpoint=/ -o canmount=noauto rpool_$poolUUID/ROOT/default
zfs create -o mountpoint=legacy -o canmount=noauto bpool_$poolUUID/BOOT/default
zfs mount rpool_$poolUUID/ROOT/default
mkdir $MOUNTPOINT/boot
mount -t zfs bpool_$poolUUID/BOOT/default $MOUNTPOINT/boot
# ash, default with busybox, does not support array
# this is word splitting
d='usr var var/lib'
for i in $d; do zfs create  -o canmount=off rpool_$poolUUID/ROOT/default/$i; done
d='srv usr/local'
for i in $d; do zfs create rpool_$poolUUID/ROOT/default/$i; done
d='log spool tmp'
for i in $d; do zfs create rpool_$poolUUID/ROOT/default/var/$i; done
zfs create -o mountpoint=/home rpool_$poolUUID/HOME/default
zfs create -o mountpoint=/root rpool_$poolUUID/HOME/default/root
zfs create rpool_$poolUUID/HOME/default/$TARGET_USERNAME

Depending on your application, separate datasets need to be created for folders inside /var/lib(not itself!)

Here we create several folders for persistent (shared) data, like we just did for /home.

d='libvirt lxc docker'
for i in $d; do zfs create rpool_$poolUUID/ROOT/default/var/lib/$i; done

lxc is for Linux container, libvirt is for storing virtual machine images, etc.

Format and mount EFI partition

Here we use /boot/efi as the mountpoint, which is default for GRUB.

mkfs.vfat -n EFI $DISK-part1
mkdir $MOUNTPOINT/boot/efi
mount -t vfat $DISK-part1 $MOUNTPOINT/boot/efi # need to specify file system

System installation

Preparation

GRUB will not find the correct path of root device without ZPOOL_VDEV_NAME_PATH=1.

export ZPOOL_VDEV_NAME_PATH=1

setup-disk refuse to run on ZFS by default, we need to add ZFS to the supported filesystem array.

sed -i 's|supported="ext|supported="zfs ext|g' /sbin/setup-disk

setup-disk

Run setup-disk to install system to target disk.

BOOTLOADER=grub USE_EFI=y setup-disk -v $MOUNTPOINT

Note that grub-probe will still fail despite ZPOOL_VDEV_NAME_PATH=YES variable set above. We will deal with this later inside chroot.

Chroot

m='dev proc sys'
for i in $m; do mount --rbind /$i $MOUNTPOINT/$i; done
chroot $MOUNTPOINT /usr/bin/env TARGET_USERPWD=$TARGET_USERPWD TARGET_USERNAME=$TARGET_USERNAME poolUUID=$poolUUID /bin/sh

Finish GRUB installation

As GRUB installation failed half-way in #Run setup-disk, we will finish it here.

Apply fix:

echo 'export ZPOOL_VDEV_NAME_PATH=YES' >> /etc/profile

Reload

source /etc/profile

GRUB fails to detect the ZFS filesystem of /boot with BusyBox stat

apk add coreutils

Missing root pool

GRUB will fail to detect rpool if rpool has unsupported features, use the following workaround:

sed -i "s|rpool=.*|rpool=\`zdb -l \${GRUB_DEVICE} \| grep -E '[[:blank:]]name' \| cut -d\\\' -f 2\`|"  /etc/grub.d/10_linux

This replaces GRUB rpool name detection.

Generate grub.cfg

After applying fixes, finally run

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

Importing pools on boot

zpool.cache will be added to initramfs and zpool command will import pools contained in this cache.

System will fail to boot without this.

zpool set cachefile=/etc/zfs/zpool.cache rpool_$poolUUID
zpool set cachefile=/etc/zfs/zpool.cache bpool_$poolUUID

Initramfs

mkinitfs included in stable Alpine Linux has bugs, see 1 and 2.

Add eudev hook and rebuild

Add eudev to /etc/mkinitfs/mkinitfs.conf.

echo 'features="ata base eudev ide scsi usb virtio nvme zfs"' > /etc/mkinitfs/mkinitfs.conf
# order of features is important! this order is tested

Rebuild initramfs with

mkinitfs $(ls -1 /lib/modules/)

Mount datasets at boot

rc-update add zfs-mount sysinit

Add user

adduser -s /bin/sh -H -D -h /home/$TARGET_USERNAME $TARGET_USERNAME
chown -R $TARGET_USERNAME /home/$TARGET_USERNAME
echo "$TARGET_USERNAME:$TARGET_USERPWD" | chpasswd

Root account is accessed via su command with root password.

Boot environment manager

bieaz is a simple boot environment management shell script with GRUB integration.

It has been submitted to aports, see this merge request. Should be available in edge/test soon.

Optional: Enable encrypted swap partition

Install cryptsetup

apk add cryptsetup

Edit the /etc/mkinitfs/mkinitfs.conf file and append the cryptsetup module to the front of zfs. Add relevant lines in fstab and crypttab. Replace $DISK with actual disk.

echo swap   $DISK-part4 /dev/urandom    swap,cipher=aes-cbc-essiv:sha256,size=256 >> /etc/crypttab
echo /dev/mapper/swap   none     swap    defaults    0   0 >> /etc/fstab

Rebuild initramfs with mkinitfs.

Finish installation

Take a snapshot for the clean installation for future use and export all pools.

exit
zfs snapshot -r rpool_$poolUUID/ROOT/default@install
zfs snapshot -r bpool_$poolUUID/BOOT/default@install

Pools must be exported before reboot, or they will fail to be imported on boot.

mount | grep -v zfs | tac | grep $MOUNTPOINT | awk '{print $3}' | \
 xargs -i{} umount -lf {}
zpool export bpool_$poolUUID
zpool export rpool_$poolUUID

Reboot

reboot

Recovery in Live environment

Boot Live environment (extended release) and repeat Preparation

Create a mount point and store encryption password in a variable:

MOUNTPOINT=`mktemp -d`
ENCRYPTION_PWD='YOUR DISK ENCRYPTION PASSWORD, 8 MINIMUM'

Find the unique UUID of your pool with

zpool import

Import rpool without mounting datasets: -N for not mounting all datasets; -R for alternate root.

poolUUID=abc123
zpool import -N -R $MOUNTPOINT rpool_$poolUUID

Load encryption key

echo $ENCRYPTION_PWD | zfs load-key -a

As canmount=noauto is set for / dataset, we have to mount it manually. To find the dataset, use

zfs list rpool_$poolUUID/ROOT

Mount / dataset

zfs mount rpool_$UUID/ROOT/$dataset

Mount other datasets

zfs mount -a

Import bpool

zpool import -N -R $MOUNTPOINT bpool_$UUID

Find and mount the /boot dataset, same as above.

zfs list bpool_$UUID/BOOT
mount -t zfs bpool_$UUID/BOOT/$dataset $MOUNTPOINT/boot # legacy mountpoint

Chroot

mount --rbind /dev  $MOUNTPOINT/dev
mount --rbind /proc $MOUNTPOINT/proc
mount --rbind /sys  $MOUNTPOINT/sys
chroot $MOUNTPOINT /bin/sh

After chroot, mount /efi

mount /boot/efi

After fixing the system, don't forget to umount and export the pools:

mount | grep -v zfs | tac | grep $MOUNTPOINT | awk '{print $3}' | \
xargs -i{} umount -lf {}
zpool export bpool_$poolUUID
zpool export rpool_$poolUUID