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Add impermanence config

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ItsDrike 2024-04-07 18:28:15 +02:00
parent 935b4094a2
commit 6051c29dd2
Signed by: ItsDrike
GPG key ID: FA2745890B7048C0
8 changed files with 221 additions and 112 deletions
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4
flake.nix
View file

@ -3,10 +3,14 @@
inputs = {
nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
home-manager = {
url = "github:nix-community/home-manager";
inputs.nixpkgs.follows = "nixpkgs";
};
# doesn't offer much above properly used symlinks but it is convenient
impermanence.url = "github:nix-community/impermanence";
};
outputs = {self, nixpkgs, ...} @ inputs: let

16
hosts/herugrim/default.nix
View file

@ -2,7 +2,6 @@
{
imports = [
./hardware-configuration.nix
./impermanence.nix
];
boot.supportedFilesystems = [ "btrfs" ];
@ -23,11 +22,26 @@
system = {
hostname = "herugrim";
username = "itsdrike";
impermanence.root = {
enable = true;
# Some people use /nix/persist/system for this, leaving persistent files in /nix subvolume
# I much prefer using a standalone subvolume for this though.
persistentMountPoint = "/persist";
# Configure automatic root subvolume wiping on boot from initrd
autoBtrfsWipe = {
devicePath = "/dev/disk/by-label/NIXROOT";
subvolumePath = "root";
cleanSnapshotPath = "root-blank";
};
};
};
device = {
virtual-machine = false;
cpu.type = "intel";
};
home-manager = {
enable = true;
stateVersion = "23.11";

110
hosts/herugrim/impermanence.nix
View file

@ -1,110 +0,0 @@
{ config, pkgs, ... }:
let
impermanence = builtins.fetchTarball "https://github.com/nix-community/impermanence/archive/master.tar.gz";
in
{
imports = [ "${impermanence}/nixos.nix" ];
users = {
# This option makes it that users are not mutable outside our configuration
# If you are using impermanence, this will actually be the case regardless of this setting,
# however, setting this explicitly is a good idea, because nix will warn us if
# our users don't have passwords set
mutableUsers = false;
# Each existing user needs to have a password file defined here
# otherwise, they will not be available to login.
# These password files can be generated using the following command:
# mkpasswd -m sha-512 > /persist/system/passwords/myuser
users = {
root = {
# password file needs to be in a volume marked `neededForRoot = true`
hashedPasswordFile = "/persist/passwords/root";
};
itsdrike = {
hashedPasswordFile = "/persist/passwords/itsdrike";
};
};
};
# Some people use /nix/persist/system instead, leaving the persistent files in /nix subvolume
# I much prefer using a standalone subvolume for this though.
environment.persistence."/persist/system" = {
hideMounts = true;
directories = [
"/etc/nixos" # nixos configuration source
"/etc/NetworkManager/system-connections" # saved network connections
"/var/db/sudo" # keeps track of who got the sudo lecture already
"/var/lib/systemd/coredump" # recorded coredumps
];
files = [
"/etc/machine-id"
# ssh stuff
"/etc/ssh/ssh_host_ed25519_key"
"/etc/ssh/ssh_host_ed25519_key.pub"
"/etc/ssh/ssh_host_rsa_key"
"/etc/ssh/ssh_host_rsa_key.pub"
];
};
# For some reason, NetworkManager needs this instead of the impermanence mode to not get screwed up
systemd.tmpfiles.rules = [
"L /var/lib/NetworkManager/secret_key - - - - /persist/system/var/lib/NetworkManager/secret_key"
"L /var/lib/NetworkManager/seen-bssids - - - - /persist/system/var/lib/NetworkManager/seen-bssids"
"L /var/lib/NetworkManager/timestamps - - - - /persist/system/var/lib/NetworkManager/timestamps"
];
boot.initrd.systemd = {
enable = true; # This enables systemd support in stage 1 - required for below setup
services.rollback = {
description = "Rollback BTRFS root subvolume to a pristine state";
wantedBy = [ "initrd.target" ];
# make sure it's done after decryption (i.e. LUKS/TPM process)
after = [ "systemd-cryptsetup@cryptfs.service" ];
# mount the root fs before clearing
before = [ "sysroot.mount" ];
unitConfig.DefaultDependencies = "no";
serviceConfig.Type = "oneshot";
script = ''
mkdir -p /mnt
# We first mount the btrfs root to /mnt
# so we can manipulate btrfs subvolumes.
mount /dev/mapper/cryptfs /mnt
# While we're tempted to just delete /root and create
# a new snapshot from /root-blank, /root is already
# populated at this point with a number of subvolumes,
# which makes `btrfs subvolume delete` fail.
# So, we remove them first.
#
# /root contains subvolumes:
# - /root/var/lib/portables
# - /root/var/lib/machines
#
# These are probably related to systemd-nspawn, but
# since I don't use it, I'm not 100% sure.
# Anyhow, deleting these subvolumes hasn't resulted in
# any issues so far, except for fairly benign-looking
# errors from systemd-tmpfiles.
btrfs subvolume list -o /mnt/root |
cut -f9 -d' ' |
while read subvolume; do
echo "deleting /$subvolume subvolume..."
btrfs subvolume delete "/mnt/$subvolume"
done &&
echo "deleting /root subvolume..." &&
btrfs subvolume delete /mnt/root
echo "restoring blank /root subvolume..."
btrfs subvolume snapshot /mnt/root-blank /mnt/root
# Once we're done rolling back to a blank snapshot,
# we can unmount /mnt and continue on the boot process.
umount /mnt
'';
};
};
}

4
options/system/default.nix
View file

@ -2,7 +2,9 @@
inherit (lib) mkOption;
in
{
imports = [ ];
imports = [
./impermanence.nix
];
options.myOptions.system = {
hostname = mkOption {

81
options/system/impermanence.nix Normal file
View file

@ -0,0 +1,81 @@
{ lib, config, ... }: with lib; let
inherit (lib) mkEnableOption mkOption literalExpression;
cfg = config.myOptions.system.impermanence;
in
{
options.myOptions.system.impermanence = {
root = {
enable = mkEnableOption ''
the Impermanence module for persisting important state directories.
'';
extraFiles = mkOption {
default = [];
example = literalExpression ''["/etc/nix/id_rsa"]'';
description = ''
Additional files in root to link to persistent storage.
'';
};
extraDirectories = mkOption {
default = [];
example = literalExpression ''["/etc/nix/id_rsa"]'';
description = ''
Additional directories in root to link to persistent storage.
'';
};
persistentMountPoint = mkOption {
default = "/persist";
description = ''
Path to a persistent directory (usually a mount point to a
standalone partition / subvolume), which will hold the persistent
system state files.
'';
};
autoBtrfsWipe = {
enable = mkOption {
default = true;
description = ''
Enable automatic wiping of the root BTRFS subvolume from initrd.
Generally, you will want to keep this enabled, as otherwise setting up
impermanence is pointless. However in case you're using a non-BTRFS
system, or you wish to set up a custom handling for this auto-wiping,
which the current handling doesn't support, disable this.
'';
};
devicePath = mkOption {
default = "/dev/mapper/cryptfs";
description = ''
Path to the BTRFS block device containing the subvolume to be wiped.
This device will be mounted from initrd.
'';
};
subvolumePath = mkOption {
default = "root";
description = ''
Path to the BTRFS subvolume to be wiped.
This is a relative path, starting from the BTRFS root.
'';
};
cleanSnapshotPath = mkOption {
default = "root-blank";
description = ''
Path to the BTRFS snapshot (subvolume) to be restore
`myOptions.system.impermanence.root.autoWipe.btrfsSubvolume` to.
This should be a blank snapshot to achieve a complete wipe.
'';
};
};
};
};
}

1
system/default.nix
View file

@ -4,6 +4,7 @@ _: {
./boot
./services
./nix
./impermanence
./programs.nix
./system.nix
./network.nix

7
system/impermanence/default.nix Normal file
View file

@ -0,0 +1,7 @@
{ inputs, ... }:
{
imports = [
inputs.impermanence.nixosModules.impermanence
./root.nix
];
}

110
system/impermanence/root.nix Normal file
View file

@ -0,0 +1,110 @@
{ config }: let
cfgSystem = config.myOptions.system;
cfg = config.myOptions.system.impermanence.root;
in
{
config = mkIf cfg.enable {
users = {
# This option makes it that users are not mutable outside of our configuration.
# If you're using root impermanence, this will actually be the case regardless
# of this setting, however, setting this explicitly is a good idea, because nix
# will warn us if our users don't have passwords set, preventing lock outs.
mutableUsers = false;
# Each existing user needs to have a password file defined here, otherwise
# they will not be available to login. These password files can be generated with:
# mkpasswd -m sha-512 > /persist/passwords/myuser
users = {
root = {
hashedPasswordFile = "${cfg.persistentMountPoint}/passwords/root";
};
${cfgSystem.username} = {
hashedPasswordFile = "${cfg.persistentMountPoint}/passwords/${cfgSystem.username}";
};
};
};
environment.persistence."${cfg.persistentMountPoint}/system" = {
hideMounts = true;
directories = [
"/etc/nixos" # NixOS configuration source
"/etc/NetworkManager/system-connections" # saved network connections
"/var/db/sudo" # keeps track of who got the sudo lecture already
"/var/lib/systemd/coredump" # captured coredumps
] ++ cfg.extraDirectories;
files = [
"/etc/machine-id"
] ++ cfg.extraFiles;
};
# For some reason, NetworkManager needs this instead of the impermanence mode
# to not get screwed up
systemd.tmpfiles.rules = [
"L /var/lib/NetworkManager/secret_key - - - - ${cfg.persistentMountPoint}/system/var/lib/NetworkManager/secret_key"
"L /var/lib/NetworkManager/seen-bssids - - - - ${cfg.persistentMountPoint}/system/var/lib/NetworkManager/seen-bssids"
"L /var/lib/NetworkManager/timestamps - - - - ${cfg.persistentMountPoint}/system/var/lib/NetworkManager/timestamps"
];
# Define host key paths in the persistent mount point instead of using impermanence for these.
# This works better, because these keys also get auto-created if they don't already exist.
services.openssh.hostKeys = mkForce [
{
bits = 4096;
path = "${cfg.persistentMountPoint}/system/etc/ssh/ssh_host_rsa_key";
type = "rsa";
}
{
bits = 4096;
path = "${cfg.persistentMountPoint}/system/etc/ssh/ssh_host_ed25519_key";
type = "ed25519";
}
];
boot.initrd.systemd = let
cfgWipe = cfg.autoBtrfsWipe;
in {
enable = true; # This enables systemd support in stage 1 - required for below setup
services.rollback-root = {
description = "Rollback BTRFS root subvolume to a pristine state";
enable = cfgWipe.enable;
wantedby = [ "initrd.target" ];
# Make sure it's done after decryption (i.e. LUKS/TPM process)
after = [ "systemd-cryptsetup@cryptfs.service" ];
# mount the root fs before clearing
before = [ "sysroot.mount" ];
unitConfig.DefaultDependencies = "no";
serviceConfig.Type = "oneshot";
script = ''
# Mount the BTRFS root to /mnt, so we can manipulate the subvolumes
mount --mkdir ${cfgWipe.devicePath} /mnt
# To restore the root subvolume, we will first delete it, and then create
# a new snapshot from the blank snapshot, which will become our new root subvolume
# However, at this point, root subvol is already populated and contains a number
# of subvolumes, which would make `btrfs subvolume delete` fail.
#
# These existing subvolumes get created automatically, and we can safely remove
# them. They are: /srv, /var/lib/portables, /var/lib/machines, /var/tmp
sudo btrfs subvolume list -o "/mnt/${cfgWipe.subvolumePath}" | cut -f9 -d' ' |
while read subvolme; do
echo "deleting $subvolume subvolume..." &&
btrfs subvolume delete "/mnt/$subvolume"
done
# Now we can remove the root subvolume, and restore it from a snapshot
echo "deleting ${cfgWipe.subvolumePath} (root) subvolume..."
btrfs subvolume delete "/mnt/${cfg.subvolumePath}"
echo "restoring ${cfgWipe.subvolumePath} (root) subvolume..."
btrfs subvolume snapshot "/mnt/${cfgWipe.cleanSnapshotPath}"
"/mnt/${cfgWipe.subvolumePath}"
# Once we're done rolling back to a blank snapshot,
# we can unmount /mnt and continue on the boot process
umount /mnt
'';
};
};
};
}