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 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)."
read -p "Please press Return to go on..."
openssl req -nodes -new -x509 -newkey rsa:4096 -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)}

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

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