if can help you!!!
have you install a guest additions in your VM?
with this you have a ""shared_folder"" options activate !!
in "host-machine" my is win7
A) create a folder to be allocated to virtual machines ( my is called "virtual" and is locate on windows-desktop)
B) open virtualbox > select my bt5-r3>settings>shared-folder> add..."virtual"..locate in my win-desktop && ACTIVATE only auto-mount && OK
C)fireup my bt5-r3 (my-virtualbox is 4.2.6)
D)open terminal & type apt-get update
E)type in terminal
cd /usr/src/linux (press-enter)
cp -rf include/generated/* include/linux/ (press-enter)
F)in the frame of "virtualbox" >> devices> install guest additions.....when the ""guest-addintions-disk"" is mounted "run" the script VBoxLinuxAdditions.run in terminal with : sh VBoxLinuxAdditions.run
G)when fishished with no error (in my case) reboot a VM ...&& after restarting my "shared-folder called virtual" is locate in /media/sf_virtual