Alaska, the District of Columbia and Georgia seems to have no law about safe passing. Most states (Alabama, California, Colorado, Delaware, Florida, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Texas, Vermont, Washington, West Virginia, Wyoming) just state you must pass at a safe distance without specifying what is considered safe.
North Carolina and Virginia define safe as 2 feet while Arizona, Arkansas, Connecticut, Illinois, Maine, Minnesota, Tennessee, Utah, Wisconsin all define 3 feet as a safe distance. My favorite is the New Hampshire law which specifies a 3 feet minimum increasing as the speed of the car increases. Oregon defines safe distance as room for the cyclist to fall into the driver's path.