Pre install windows 8 comes with UEFI secure boot enabled
(UEFI which substitutes what we have known as the BIOS)
which prevent unrecognized source to boot or Linux
But latest version of Ubuntu have support for the UEFI boot see (you doesn't mention which Ubuntu version you are using) https://help.ubuntu.com/community/UEFI
So there is no problem in dual boot Ubuntu with windows 8
for your convenient (solve your problem ) you can off the UEFI secure boot in some easy step they are
1 ) while holding shift key click on restart option (from power)
2 ) windows will show you option then select Troubleshoot
3 ) select advanced options
4 ) select UEFI frameware settings then disable it after restart
Here is the video
Then you are able to boot ubuntu and even old version of the Linux which couldn’t install before in windows 8 .
in dual boot if you don’t get the windows 8 listed in grub menu then
type following command in terminal while mounting drive which have windows installed
sudo update-grub2