Visible white smoke typically indicates water and/or oil seepage into the combustion chambers. Water has an opportunity to enter the combustion chambers via a damaged head gasket, at the junction of an engine's valve head and engine block. It is best a smog check repair station or automotive repair shop conduct an inspection to find the actual fault.
Excessive white smoke is normally emitted typically on cold days, and when the engine is not properly warmed up. White smoke during startup or during cold weather is just steam, and will not cause a smog test failure.
Since the vehicle failed a smog check because of white smoke, you may be eligible for the CAP Repair Program for low income applicants.