The apparmor for VirtualBox is not existed in
/etc/apparmor.d/and you should build your own. You can copy the following source code to the directory and enable it.
Step 1 :
sudo apt-get install apparmor-utils
Make sure Virtualbox is installed.
Step 2 :
Copy the captioned source code and placed it to
/etc/apparmor.d/and name them as the name that is underlined.
Step 3 :
sudo aa-enforce /etc/apparmor.d/usr.bin.VBox
That's all! See you.
Apparmor manual for Ubuntu