mirror of
https://github.com/ItsDrike/nixdots
synced 2024-12-26 18:34:35 +00:00
179 lines
6.8 KiB
Markdown
179 lines
6.8 KiB
Markdown
# Secure Boot
|
|
|
|
This guide will show you how to set up UEFI Secure Boot with NixOS. Once finished, you will be left with a system that
|
|
doesn't allow booting any untrusted EFI images (other operating systems, fraudulently modified kernels) on your machine.
|
|
|
|
This guide assumes you're following from the [INSTALLATION](./01_INSTALLATION.md) guide, and that
|
|
you have converted your config to a flake.
|
|
|
|
## Make sure you're using UEFI
|
|
|
|
As a first step, you will want to confirm that you really are on a UEFI system. If you're using any recent hardware,
|
|
this is very likely the case. Nevertheless, let's check and make sure:
|
|
|
|
```shell
|
|
bootctl status
|
|
```
|
|
|
|
Make sure the `Firmware` is reported as `UEFI`.
|
|
|
|
## Security requirements
|
|
|
|
The requirements are optional, as it is possible to set up secure boot without them. That said, they are heavily
|
|
encouraged, as without these, setting up secure boot will not be a very effective security measure.
|
|
|
|
First requirement is to set up a **BIOS Password**. This is a password that you will be asked for every time you wish to
|
|
enter the BIOS (UEFI). This is necessary, as without it, an attacker could very easily just go to the BIOS and disable
|
|
Secure Boot.
|
|
|
|
The second requirement is having **disk encryption**, at least for the root (or persist, if using impermanence)
|
|
partition. This is important, because the UEFI signing keys will be stored here, and you don't want someone to
|
|
potentially be able to get access to them, as it would allow them to sign any malicious images, making them pass secure
|
|
boot.
|
|
|
|
> [!NOTE]
|
|
> Even after following all of these, you should be aware that Secure Boot isn't an unbreakable solution. In
|
|
> fact, if someone is able to get a hold of your machine, they can simply pull out the CMOS battery, which usually
|
|
> resets the UEFI. That means turning off Secure Boot, and getting rid of the BIOS password.
|
|
>
|
|
> While Secure Boot is generally a good extra measure to have, it is by no means a reliable way to really prevent
|
|
> others from ever being able to boot untrusted systems, unless you use a specialized motherboard, which persists the
|
|
> UEFI state.
|
|
|
|
## Create your keys
|
|
|
|
To create secure boot keys, you can use `sbctl`, which is a very popular Secure Boot Key Manager. It is available in
|
|
nixpkgs as `pkgs.sbctl`. Make sure to add it to your configuration.
|
|
|
|
> [!IMPORTANT]
|
|
> If you have set up impermanence, you will first need to declare `/etc/secureboot` as a persistent directory. This
|
|
> directory will contain the secure boot keys necessary to sign the bootloader and your kernel/initrd images. If you
|
|
> lose this key, you will need to go through this process again.
|
|
|
|
Once you have sbctl installed, run the following command to create your new keys:
|
|
|
|
```shell
|
|
sudo sbctl create-keys
|
|
```
|
|
|
|
This takes a couple of seconds. When it is done, your Secure Boot keys are located in `/etc/secureboot`. sbctl sets the
|
|
permissions of the secret key so that only root can read it.
|
|
|
|
## lanzaboote
|
|
|
|
`lanzaboote` is a tool to help you set up secure boot in NixOS. To install it, you can add it as an input for your
|
|
flake:
|
|
|
|
```nix
|
|
lanzaboote = {
|
|
url = "github:nix-community/lanzaboote/v0.3.0";
|
|
|
|
# Optional but recommended to limit the size of your system closure.
|
|
inputs.nixpkgs.follows = "nixpkgs";
|
|
};
|
|
```
|
|
|
|
And include the `lanzaboote.nixosModules.lanzaboote` module.
|
|
|
|
Now, you will want to add the following to your configuration:
|
|
|
|
```nix
|
|
# Lanzaboote replaces systemd-boot
|
|
boot.loader.systemd-boot.enable = lib.mkForce false;
|
|
|
|
boot.lanzaboote = {
|
|
enable = true;
|
|
pkiBundle = "/etc/secureboot";
|
|
};
|
|
```
|
|
|
|
You can now rebuild your system: `sudo nixos-rebuild switch --flake .`.
|
|
|
|
## Check that your machine is ready for secure-boot environment
|
|
|
|
After you rebuild your system, check `sudo sbctl verify` output. You should see it report all of your boot entries as
|
|
signed.
|
|
|
|
Note that files ending with `bzImage.efi` do not need to be signed.
|
|
|
|
### Manually sign an image
|
|
|
|
In case you'd ever need to do so, it is possible to sign an image manually with `sbctl`. To do so, you can run:
|
|
|
|
```shell
|
|
sbctl sign -s /boot/my_image.efi
|
|
```
|
|
|
|
The `-s` flag means save. This makes sure the files will be automatically re-signed when we update. (List of files to
|
|
re-sign will be stored in the secure boot database, in `/etc/secureboot`)
|
|
|
|
Note that you shouldn't really need to use this.
|
|
|
|
## Enabling secure boot
|
|
|
|
Now that NixOS is ready for secure-boot, we will set up firmware. At the end of this section, Secure Boot will be
|
|
enabled on your system and your firmware will only boot binaries that are signed with your keys.
|
|
|
|
### Enter Setup mode
|
|
|
|
To allow us to upload new signing keys into the UEFI firmware, we will need to enter "setup mode". This should be
|
|
possible by going to the Secure Boot category in your UEFI settings, and clicking on Delete/Clear certificates, or
|
|
there could even be a "Setup Mode" option directly.
|
|
|
|
This option may not be available without also enabling secure boot. This is fine, while in setup mode, the secure
|
|
boot checks will not be performed.
|
|
|
|
You can now save the settings and reboot.
|
|
|
|
Once booted, to check that you really are in Setup Mode, run:
|
|
|
|
```shell
|
|
sudo sbctl status
|
|
```
|
|
|
|
### Enroll the new keys
|
|
|
|
You will now have to enroll your new keys to activate Secure Boot.
|
|
|
|
```shell
|
|
sudo sbctl enroll-keys -m
|
|
```
|
|
|
|
> [!WARNING]
|
|
> The `-m` option (also known as `--microsoft`) will make sure to also include the Microsoft
|
|
> signing keys. This is required by most motherboards, not using it could brick your device.
|
|
|
|
> [!NOTE]
|
|
> If you encounter "File is immutable" warnings after running sbctl, it should be safe to simply add the `-i` (or
|
|
> `--ignore-immutable`) flag, which will run `chattr` and remove the immutable flags from these files for you.
|
|
>
|
|
> If you still encounter errors even with this flag, it means you have probably done something wrong when entering the
|
|
> setup mode. Try looking for a option like "Reset keys" in your UEFI, then try this again.
|
|
|
|
This should automatically enable secure boot in user mode for you. You can now **reboot the system**.
|
|
|
|
### Make sure it worked
|
|
|
|
To check that you really are using secure-boot, you can run
|
|
|
|
```shell
|
|
bootctl status
|
|
```
|
|
|
|
It should report `Secure Boot: enabled (user)`.
|
|
|
|
## Why bother?
|
|
|
|
As I mentioned, secure boot can be bypassed if someone tries hard enough (pulling the CMOS battery). That then
|
|
brings to question whether it's even worth it to set it up, when it doesn't really give you that much. On its own,
|
|
|
|
I probably wouldn't bother with setting up secure-boot, however secure boot allows me to set up TPM (Trusted Platform
|
|
Module) to automatically release the decryption keys for my LUKS encrypted root partition, in a secure way. This means I
|
|
won't have to type my disk password every time I boot.
|
|
|
|
For more information on this, check out the follow-up guide: [TPM_UNLOCKING](./04_TPM_UNLOCKING.md).
|
|
|
|
## Sources / Attribution
|
|
|
|
- <https://github.com/nix-community/lanzaboote/blob/master/docs/QUICK_START.md>
|