Typically white smoke is a sign that coolant or water is leaking into the exhaust chamber. You can also smell it in the exhaust gas if you're burning either coolant or oil. Some day soon you should let the car idle in your driveway, and then have a friend apply the gas while in neutral while you stand back and get a whif of the smoke

. It is a pretty ghetto plan, but then you'll know if it's oil or coolant without having to take things apart.
If it's oil though you would probably have bad valve seals or even small amount of oil in your spark plug holes from a bad valve cover gasket. If you pull out your spark plug wires and plugs, and find oil around the tips then that may be the culprit. If you are leaking coolant, it is most likely a bad head gasket or in an extreme case maybe a warped head.