vyos-documentation/docs/installation/secure-boot.rst

.. _secure_boot:

###########
Secure Boot
###########

Initial UEFI secure boot support is available (:vytask:`T861`). We utilize
``shim`` from Debian 12 (Bookworm) which is properly signed by the UEFI
SecureBoot key from Microsoft.

.. note:: There is yet no signed version of ``shim`` for VyOS, thus we
   provide no signed image for secure boot yet. If you are interested in
   secure boot you can build an image on your own.

To generate a custom ISO with your own secure boot keys, run the following
commands prior to your ISO image build:

.. code-block:: bash

  cd vyos-build
  openssl req -new -x509 -newkey rsa:4096 \
    -keyout data/live-build-config/includes.chroot/var/lib/shim-signed/mok/MOK.key \
    -out data/live-build-config/includes.chroot/var/lib/shim-signed/mok/MOK.der \
    -outform DER -days 36500 -subj "/CN=MyMOK/" -nodes
  openssl x509 -inform der \
    -in data/live-build-config/includes.chroot/var/lib/shim-signed/mok/MOK.der \
    -out data/live-build-config/includes.chroot/var/lib/shim-signed/mok/MOK.pem

************
Installation
************

As our version of ``shim`` is not signed by Microsoft we need to enroll the
previously generated :abbr:`MOK (Machine Owner Key)` to the system.

First of all you will need to disable UEFI secure boot for the installation.

.. figure:: /_static/images/uefi_secureboot_01.png
   :alt: Disable UEFI secure boot

Proceed with the regular VyOS :ref:`installation <permanent_installation>` on
your system, but instead of the final ``reboot`` we will enroll the
:abbr:`MOK (Machine Owner Key)`.

.. code-block:: none

  vyos@vyos:~$ install mok
  input password:
  input password again:

The requested ``input password`` can be user chosen and is only needed after
rebooting the system into MOK Manager to permanently install the keys.

With the next reboot, MOK Manager will automatically launch

.. figure:: /_static/images/uefi_secureboot_02.png
   :alt: Disable UEFI secure boot

Select ``Enroll MOK``

.. figure:: /_static/images/uefi_secureboot_03.png
   :alt: Disable UEFI secure boot

You can now view the key to be installed and ``continue`` with the Key installation

.. figure:: /_static/images/uefi_secureboot_04.png
   :alt: Disable UEFI secure boot

.. figure:: /_static/images/uefi_secureboot_05.png
   :alt: Disable UEFI secure boot

Now you will need the password previously defined

.. figure:: /_static/images/uefi_secureboot_06.png
   :alt: Disable UEFI secure boot

Now reboot and re-enable UEFI secure boot.

.. figure:: /_static/images/uefi_secureboot_07.png
   :alt: Disable UEFI secure boot

VyOS will now launch in UEFI secure boot mode. This can be double-checked by running
either one of the commands:

.. code-block:: none

  vyos@vyos:~$ show secure-boot
  SecureBoot enabled

.. code-block:: none

   vyos@vyos:~$ show log kernel | match Secure
   Oct 08 19:15:41 kernel: Secure boot enabled

.. code-block:: none

    vyos@vyos:~$    show version
    Version:          VyOS 1.5-secureboot
    Release train:    current
    Release flavor:   generic

    Built by:         autobuild@vyos.net
    Built on:         Tue 08 Oct 2024 18:00 UTC
    Build UUID:       5702ca38-e6f4-470f-b89e-ffc29baee474
    Build commit ID:  9eb61d3b6cf426

    Architecture:     x86_64
    Boot via:         installed image
    System type:      KVM guest
    Secure Boot:      enabled   <-- UEFI secure boot indicator

    Hardware vendor:  QEMU
    Hardware model:   Standard PC (i440FX + PIIX, 1996)
    Hardware S/N:
    Hardware UUID:    1f6e7f5c-fb52-4c33-96c9-782fbea36436

    Copyright:        VyOS maintainers and contributors

************
Image Update
************

.. note:: There is yet no signed version of ``shim`` for VyOS, thus we
   provide no signed image for secure boot yet. If you are interested in
   secure boot you can build an image on your own.

During image installation you will install your :abbr:`MOK (Machine Owner
Key)` into the UEFI variables to add trust to this key. After enabling
secure boot support in UEFI again, you can only boot into your signed image.

It is no longer possible to boot into a CI generated rolling release as those
are currently not signed by a trusted party (:vytask:`T861` work in progress).
This also means that you need to sign all your successor builds you build on
your own with the exact same key, otherwise you will see:

.. code-block:: none

  error: bad shim signature
  error: you need to load the kernel first

************
Linux Kernel
************

In order to add an additional layer of security that can already be used in nonesecure
boot images already is ephem,eral key signing of the Linux Kernel modules.

https://patchwork.kernel.org/project/linux-integrity/patch/20210218220011.67625-5-nayna@linux.ibm.com/

Whenever our CI system builds a Kernel package and the required 3rd party modules,
we will generate a temporary (ephemeral) public/private key-pair that's used for signing the
modules. The public key portion is embedded into the Kernel binary to verify the loaded
modules.

After the Kernel CI build completes, the generated key is discarded - meaning we can no londer
sign additional modules with out key. Our Kernel configuration also contains the option
``CONFIG_MODULE_SIG_FORCE=y`` which means that we enforce all modules to be signed. If you
try to load an unsigned module, it will be rejected with the following error:

``insmod: ERROR: could not insert module malicious.ko: Key was rejected by service``

Thos we close the door to load any malicious stuff after the image was assembled into the
Kernel as module. You can of course disable this behavior on custom builds.

************
Troubleshoot
************

In most of the cases if something goes wrong you will see the following error message
during system boot:

.. code-block:: none

  error: bad shim signature
  error: you need to load the kernel first

This means that the Machine Owner Key used to sign the Kernel is not trusted by your
UEFI. You need to install the MOK via ``install mok`` as stated above.