chore: update installation guide with secure-boot setup pitfalls

Reviewed-on: #93

INSTALLATION.md

@@ -149,6 +149,16 @@ $ sudo sbctl enroll-keys
   Don't force it, either trust exactly those with `--tpm-eventlog` or
   microsoft's keys with `--microsoft`. Without either, the firmware may not
   start the device, in the worst case the machine doesn't boot at all.
+- Check what sbctl found first, a real option ROM has a PCI device path:
+```bash
+$ sudo nix shell nixpkgs#tpm2-tools -c tpm2_eventlog /sys/kernel/security/tpm0/binary_bios_measurements | grep -A14 "EV_EFI_BOOT_SERVICES_DRIVER"
+```
+- Paths starting with `0407` (firmware volume) are drivers from the firmware
+  itself, not option ROMs (e.g. on the ThinkPad). `--tpm-eventlog` trusts
+  exactly those, after a firmware update they may need to be enrolled again
+  (disable Secure Boot, `sbctl enroll-keys --tpm-eventlog`)
+- Without an integrated gpu (argon), the gpu's option ROM draws the firmware
+  setup too, use `--microsoft` there, a refused gpu means no picture at all
 
 6. enable Secure Boot in the firmware and set a firmware password, then check
 ```bash
@@ -158,6 +168,25 @@ $ sudo sbctl status                     # Secure Boot: ✓ Enabled
 - If it doesn't boot anymore, disabling Secure Boot in the firmware boots as before
 - Losing the keys isn't fatal: erase the keys in the firmware and start over at step 1
 
+## how to unlock the disk with the tpm (laptops)
+Needs Secure Boot first. The TPM releases the key only with the PIN and while
+the Secure Boot state (PCR 7) is unchanged. The passphrase stays as fallback.
+
+1. enroll the TPM with a PIN as an additional key slot
+```bash
+# asks for the current passphrase, then the new PIN
+$ sudo systemd-cryptenroll --tpm2-device=auto --tpm2-pcrs=7 --tpm2-with-pin=yes /dev/disk/by-label/nixcrypt
+```
+
+2. import `modules/nixos/tpm-unlock.nix` in the host's `configuration.nix`, rebuild and reboot
+
+- If the passphrase is suddenly asked for instead of the PIN, the Secure Boot
+  state changed. After a firmware update that's expected, otherwise investigate
+  before typing the passphrase. To re-enroll:
+```bash
+$ sudo systemd-cryptenroll --wipe-slot=tpm2 --tpm2-device=auto --tpm2-pcrs=7 --tpm2-with-pin=yes /dev/disk/by-label/nixcrypt
+```
+
 ## how to upgrade the system
 ```bash
 $ cd /path/to/repo

hosts/argon/configuration.nix

@@ -12,6 +12,7 @@
     ../../modules/nixos/data-drives.nix
     ../../modules/nixos/gnupg.nix
     ../../modules/nixos/greetd.nix
+    ../../modules/nixos/lanzaboote.nix
     ../../modules/nixos/locales.nix
     ../../modules/nixos/networking.nix
     ../../modules/nixos/niri.nix
@@ -23,6 +24,7 @@
     ../../modules/nixos/settings.nix
     ../../modules/nixos/steam.nix
     ../../modules/nixos/thunar.nix
+    ../../modules/nixos/tpm-unlock.nix
     ../../modules/nixos/users.nix
     ../../modules/nixos/vial.nix
   ];

hosts/krypton/configuration.nix

@@ -24,6 +24,7 @@
     ../../modules/nixos/services.nix
     ../../modules/nixos/settings.nix
     ../../modules/nixos/steam.nix
+    ../../modules/nixos/tpm-unlock.nix
     ../../modules/nixos/users.nix
     ../../modules/nixos/vial.nix
   ];
@@ -31,6 +32,13 @@
   # host-specific niri config (input devices, laptop binds)
   home-manager.users.aaron.imports = [ ./niri.nix ];
 
+  # hidpi panel (2880x1920): the sddm greeter runs in weston, which doesn't scale
+  services.displayManager.sddm.settings.General.GreeterEnvironment = "QT_SCALE_FACTOR=2";
+
+  # bigger boot menu font, mode found with "r" in the menu; mode 6 is beyond
+  # what boot.loader.systemd-boot.consoleMode accepts, so set via lanzaboote
+  boot.lanzaboote.settings.console-mode = "6";
+
   networking.hostName = "krypton";
   system.stateVersion = "26.05"; # don't change
 }

hosts/neon/configuration.nix

@@ -17,6 +17,7 @@
     ../../modules/nixos/certificates.nix
     ../../modules/nixos/docker.nix
     ../../modules/nixos/gnupg.nix
+    ../../modules/nixos/lanzaboote.nix
     ../../modules/nixos/locales.nix
     ../../modules/nixos/networking.nix
     ../../modules/nixos/niri.nix
@@ -28,6 +29,7 @@
     ../../modules/nixos/services.nix
     ../../modules/nixos/settings.nix
     ../../modules/nixos/steam.nix
+    ../../modules/nixos/tpm-unlock.nix
     ../../modules/nixos/users.nix
     ../../modules/nixos/vial.nix
   ];

modules/nixos/bootloader.nix

@@ -4,6 +4,8 @@
   # set bootloader to systemd
   boot.loader = {
     systemd-boot.enable = true;
+    # no kernel command line editing at the boot menu (e.g. init=/bin/sh)
+    systemd-boot.editor = false;
     efi.canTouchEfiVariables = true;
   };
 

modules/nixos/tpm-unlock.nix

@@ -0,0 +1,8 @@
+# Unlock cryptroot with the TPM and a PIN, the passphrase stays as fallback.
+# The TPM only releases the key while PCR 7 (the Secure Boot state) matches,
+# so this needs lanzaboote.nix. Enrolled once per host with
+# `systemd-cryptenroll`, see INSTALLATION.md.
+
+{
+  boot.initrd.luks.devices."cryptroot".crypttabExtraOpts = [ "tpm2-device=auto" ];
+}