Secure Kernel Extension Loading is a new security feature of macOS High Sierra. macOS now requires you to manually approve the installation of third party kernel extensions.
During Vallum installation you may see a popup alert with an error message: “System Extension Blocked”.
To successfully complete Vallum installation process you need to explicitly allow the execution of Vallum. To do so just open macOS System Preferences and browse to Security & Privacy -> General then allow software by Davide Feroldi. More information about Secure Kernel Extension Loading can be found here