Make DKMS sign kernel modules on installation, with full script support and somewhat distro independent

dkms-module-signing.md

On systems with UEFI Secure Boot enabled, recent Linux kernels will only load signed modules, so it's about time DKMS grew the capability to sign modules it's building.

These scripts are extended and scriptified variants of https://computerlinguist.org/make-dkms-sign-kernel-modules-for-secure-boot-on-ubuntu-1604.html and https://askubuntu.com/questions/760671/could-not-load-vboxdrv-after-upgrade-to-ubuntu-16-04-and-i-want-to-keep-secur/768310#768310 and add some error checking, a passphrase around your signing key, and support for compressed modules.

dkms-sign-module is a wrapper for the more generic sign-modules which can also be used outside of DKMS.

Installation

1. Create a directory under /root, say /root/module-signing, put the three scripts below in there and make them executable: chmod u+x one-time-setup sign-modules dkms-sign-module
2. Run one-time-setup
3. Reboot your computer to deploy the MOK
4. For each module you will want to sign via DKMS, create a file /etc/dkms/<module_name>.conf with the following content:

   POST_BUILD=../../../../../../root/module-signing/dkms-sign-module
   

   The awkward relative pathname is important since DKMS prepends its own path to it, so an absolute path will not work.

dkms-sign-module

#!/bin/bash
export PROMPT="Enter Machine Owner Key (MOK) passphrase to sign $module $module_version: "
export KERNELVER=$kernelver
$(dirname $0)/sign-modules ../$kernelver/$arch/module/*.ko*

one-time-setup

#!/bin/bash

mydir=$(dirname $0)

echo "I am about to generate the Machine Owner Key (MOK)."
echo "The passphrase you enter for this key will be required every time you want to sign a module."
read -p "Please press Return to go on..."
openssl req -new -x509 -newkey rsa:2048 -keyout $mydir/MOK.priv -outform DER -out $mydir/MOK.der -days 36500 -subj "/CN=$(hostname) module signing key/" || exit 1

echo
echo "Now I will import the generated key into the secure keystore."
echo "The passphrase you will enter is only required once, during the following reboot."
read -p "Please press Return to go on..."
mokutil --import $mydir/MOK.der || exit 1

echo
echo "Please reboot your computer now to complete the enrollment of your new MOK."
echo "This is going to look somewhat similar to https://sourceware.org/systemtap/wiki/SecureBoot"

sign-modules

#!/bin/bash

if [[ -z "$1" ]]; then
    echo "Usage: $0 module [module...]"
    exit 1
fi

mydir=$(dirname $0)

PROMPT="${PROMPT:-Enter Machine Owner Key (MOK) passphrase: }"
KERNELVER=${KERNELVER:-$(uname -r)}

read_passphrase() {
    # We write to /dev/tty to get around DKMS' redirection to /dev/null if it's being run with -q (e.g. during rpm installs)
    echo -n "$PROMPT" > /dev/tty
    read -s KBUILD_SIGN_PIN < /dev/tty
    export KBUILD_SIGN_PIN
    echo > /dev/tty
    openssl rsa -check -noout -passin env:KBUILD_SIGN_PIN -in $mydir/MOK.priv > /dev/null 2>&1
}

do_sign() {
    /lib/modules/$KERNELVER/build/scripts/sign-file sha256 $mydir/MOK.priv $mydir/MOK.der "$1"
}

while ! read_passphrase; do echo "Wrong passphrase, please try again."; done

for module in $@; do
    echo "Signing module: $module"
    module_basename=${module:0:-3}
    module_suffix=${module: -3}
    if [[ "$module_suffix" == ".xz" ]]; then
	unxz $module
	do_sign $module_basename
	xz -f $module_basename
    elif [[ "$module_suffix" == ".gz" ]]; then
	gunzip $module
	do_sign $module_basename
	gzip -9f $module_basename
    else
	do_sign $module
    fi    
done

Thanks Xu Zhen but above solution won't work as UEFI Secure Boot is disabled. Could anyone please assist me as not able to install VirtualBox 6.1 on Ubuntu 20.04 (Windows host)as getting error [ (i have changed the kernel version from default to 5.7.0-microsoft-standard but still no luck): Tried so many things but nothing works]:

Loading new virtualbox-6.1.6 DKMS files...
It is likely that 5.7.0-microsoft-standard belongs to a chroot's host
Building for 4.19.0-041900-generic, 5.4.0-39-generic, 5.4.0-40-generic and 5.6.0-1017-oem
Building initial module for 4.19.0-041900-generic
ERROR (dkms apport): kernel package linux-headers-4.19.0-041900-generic is not supported
Error! Bad return status for module build on kernel: 4.19.0-041900-generic (x86_64)
Consult /var/lib/dkms/virtualbox/6.1.6/build/make.log for more information.
dpkg: error processing package virtualbox-dkms (--configure):
installed virtualbox-dkms package post-installation script subprocess returned error exit status 10

virtualbox
WARNING: The vboxdrv kernel module is not loaded. Either there is no module
available for the current kernel (5.7.0-microsoft-standard) or it failed to
load. Please recompile the kernel module and install it by

       sudo /sbin/vboxconfig

     You will not be able to start VMs until this problem is fixed.

Qt WARNING: could not connect to display
Qt FATAL: This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.
Aborted

Note for those still using these scripts: in sign-modules, xz needs to be passed -C crc32 (see lwfinger/rtw88#189 for details; tldr: xz now uses CRC64, which the kernel is not able to deal with, leading to module decompression errors).