Setting up virtualbox on arch (the best way)

sudo pacman -Syu virtualbox virtualbox-host-dkms linux-headers

rebuild kernel modules

sudo dkms autoinstall

# load modules manually
sudo modprobe vboxdrv
sudo modprobe vboxnetflt
sudo modprobe vboxnetadp
sudo modprobe vboxpci

# check if modules are loaded correctly
lsmod | grep vbox

After that you can reboot virtualbox or reboot the system