Sign vboxdrv so Secure Boot has no problem with it. (Source AskUbuntu)
Short version:

sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ~/.ssh/MOK.priv .ssh/MOK.der $(modinfo -n vboxdrv)

To create the keys MOK.priv and MOK.der, this steps are required:

# create key pair
openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=Signing Key for Secure Boot/"

# use mokutil to test, if the key is enrolled (should not, if you just created it)
mokutil --test-key .ssh/MOK.der

# import key
sudo mokutil --import .ssh/MOK.der

# sign vboxdrv
sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 .ssh/MOK.priv .ssh/MOK.der $(modinfo -n vboxdrv)

# check vboxdrv and activate
sudo modinfo -n vboxdrv
sudo modprobe vboxdrv