Are there any restrictions for drilling holes in solid lumber joists regarding how close to the ends of the joist?
It has to be at least 2" away from the top, or bottom of the joist. As far as distance from the ends, there are no rules:


  Holes: Do not bore holes closer than 2" from joist edges, nor make them larger than 1/3 the depth of the joist. –engineering.purdue.edu, PDF


If you look at the document, it clearly states and depicts the top or bottom, with no mention of an "end".