I added a Mojave virtual machine to VirtualBox on my Mac running Monterey, but suddenly neither of my virtual machines would launch, each spewed a message like this:

virtualbox Kernel driver not installed (rc=-1908) Make sure the kernel module has been loaded successfully. where: suplibOsInit what: 3 VERR_VM_DRIVER_NOT_INSTALLED (-1908) - The support driver is not installed. On linux, open returned ENOENT.

and

Error Domain=KMErrorDomain Code=27 "Extension with identifiers org.virtualbox.kext.VBoxDrv,org.virtualbox.kext.VBoxNetAdp,org.virtualbox.kext.VBoxNetFlt,org.virtualbox.kext.VBoxUSB not approved to load. Please approve using System Preferences." UserInfo={NSLocalizedDescription=Extension with identifiers org.virtualbox.kext.VBoxDrv,org.virtualbox.kext.VBoxNetAdp,org.virtualbox.kext.VBoxNetFlt,org.virtualbox.kext.VBoxUSB not approved to load. Please approve using System Preferences.}

Then I finally realized what the problem was. I had recently disabled SIP. To fix the issues above, I had to re-enable SIP following these steps:

1. Reboot Mac in recovery mode, hold command and R when restarting your Mac.
2. In recovery mode, open Terminal.app and execute the command “csrutil enable”.
3. Restart your Mac and log in as usual.
4. Launch VirtualBox and then open System Preferences->Security and allow access to Oracle. You may have to reboot one more time after doing this.

Before figuring this out, I had also uninstalled and reinstalled VirtualBox, but I’m not convinced that is completely necessary.