If you accidentally delete or modify a kext this method will help you restore it. The easiest way is restore from TimeMachine backup.
If you do not have any backup...
1. Download the Mavericks image from App Store
2. Install Pacifist from CharlesSoft
3. Open with Pacifist:
/Applications/Install OS X Mavericks.app/Contents/SharedSupport/OSInstall.mpkg
4. Find and select Extensions folder: