I recently upgraded my Fedora 20 with the latest kernel and came across an issue when I wanted to boot my Windows VM. VirtualBox told me to setup vboxdrv again, which refused to work, stopping the the error message:
DKMS: add completed. Failed to install using DKMS, attempting to install without Makefile:183: * Error: unable to find the sources of your current Linux kernel. Specify KERN_DIR=<directory> and run Make again. Stop.</directory>
The only thing that helped was to remove VirtualBox altogether.
yum remove VirtualBox-4.3
And then reinstall it from rpmfusion with the kmod meta-package which install VirtualBox alongside the correct kernel sources.
yum install VirtualBox kmod-VirtualBox
After installing the VirtualBox extensions I was able to bring my Windows VM back up.