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How to get started with Lanzaboote-based SecureBoot?

Requirements :

Using systemd-boot
Either the private certificate to sign files or control over your SecureBoot keys to insert your own, read the section on how to enroll your keys

Disclaimer : This project bring its own UEFI stub to circumvent the difficulty introduced by UKI model where everything has to baked in. The authors are aware of the concept of "extending" initrds through https://github.com/systemd/systemd/blob/main/src/boot/efi/stub.c#L23. We are exploring this avenue to minimize our dependency on this custom stub, but, we want to explore the full needs of the NixOS usecases first.

Enrolling your own keys

Disclaimer : Some device firmware, e.g. GPU (so-called OpROMs) get executed at boot, replacing your platform keys with your own, can cause them to not run anymore under SecureBoot, as they are signed using [Microsoft Corporation UEFI CA 2011 certificate], aka the Microsoft 3rd Party UEFI CA certificate. To know about limited mitigations regarding this, read the "keeping Microsoft keys" subsection.

Disclaimer : TPMs interaction are out of scope for this project, please read more about TPM eventlog, but note that Lanzastub do not implement any TPM event logging for now.

Entering into Setup Mode

Depending on your machine, you need:

either, to reset your keys to enter into Setup Mode (removing your Microsoft keys!)
either, to allow changes to your keys from your running system (possibly, keeping your Microsoft keys)

These instructions varies on your BIOS, see https://www.rodsbooks.com/efi-bootloaders/controlling-sb.html#setuputil for an example.

You can confirm to be in Setup Mode using bootctl status, reading Secure Boot line, which should show a line similar to: Secure Boot: no (setup mode).

In this context, note that /sys/firmware/efi/efivars/ becomes writeable from your Linux system.

Bricking your machine in a bad way can happen if this location gets overwritten by a strange command / program. ^[I already rm'd -rf this location once, it was very not funny.]

Installing your keys

Easy way: `sbctl`

sbctl has static locations for keys, in nixpkgs, sbctl writes to /etc/secureboot, so prepare a directory for this location with the right permissions.

Creating keys is: sbctl create-keys
Rotating keys is: sbctl rotate-keys (with sbctl ≥ 0.10)

For enrollment, first, read the next subsection:

Keeping Microsoft keys

If you want to keep Microsoft keys, run:

$ sbctl enroll-keys --microsoft

It will include Microsoft Corporation UEFI CA 2011 certificate.

It does not guarantee that everything will work out of the box, it may be the case you have other certificates that should be included from your OEM which are not distributed in sbctl.

Therefore, please double check everything until this project can provide better guarantees.

Ignoring Microsoft keys

If you want to remove Microsoft keys, you have very good reasons to do so (i.e. not trusting Microsoft to not give a valid certificate to OEM which could pose risk to your threat model), run:

$ sbctl enroll-keys --yes-this-might-brick-my-machine

The authors of this project declines all responsibility for running this command and bricking your machine, this is experimental SecureBoot.

Harder ways: follow the Archlinux Wiki

Read about this on https://wiki.archlinux.org/title/Unified_Extensible_Firmware_Interface/Secure_Boot#Enrolling_keys_in_firmware.

Using the `Lanzaboote` project in your NixOS configuration

Disclaimer : Lanzaboote requires RFC-0125 aka bootspec on your system, this is automatically enabled on your behalf.

Warning : Lanzaboote is compatible only with systemd-boot for now, also, it replaces boot.loader.systemd-boot and has no feature parity with this NixOS module.

Use your favorite way to import this project in your configuration, i.e. Flakes or niv or fetchFromGitHub:

`fetchFromGitHub`

{ pkgs, config, lib, ... }: 
{
  imports = [
    (pkgs.fetchFromGitHub {
      owner = "nix-community";
      repo = "lanzaboote";
      rev = "relevant-revision";
      sha256 = lib.fakeHash;
    })
  ];
}

Now, assuming the NixOS module is imported, you only need to have:

{ pkgs, config, lib, ... }: {
  boot.lanzaboote = {
    enable = true;
    publicKeyFile = "/etc/secureboot/keys/db/db.pem"; # DB public key
    privateKeyFile = "/etc/secureboot/keys/db/db.key"; # DB private key
  };
}

Different options can be added:

boot.lanzaboote.pkiBundle: provide the whole PKI bundle generated by sbctl create-keys, useful when you want to automate key enrollment, security warning: those will be copied at system activation in /tmp/pki to perform the enrollment because sbctl do not support dynamic arbitrary paths for now.
boot.lanzaboote.enrollKeys: perform automatic enrollment key, if needed, at each rebuild

Known limitations

Generations are shown improperly because /etc/os-release induces the wrong name in the systemd-boot menu according to this algorithm: <>
$esp/nixos is a hardcoded path to store initrds & kernels
The lifecycle between disabling Lanzaboote and getting back into Lanzaboote is not clear
No TPM event logging & measurements is taking place
Alternative Nix store locations are not supported
PKCS#11 engine support is not available

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