[RPG] Do ability modifiers get added to each roll when achieving a critical hit?

From Combat Statistics, SRD:

Multiplying Damage

Sometimes you multiply damage by some factor, such as on a critical hit. Roll the damage (with all modifiers) multiple times and total the results. Note: When you multiply damage more than once, each multiplier works off the original, unmultiplied damage.

Exception: Extra damage dice over and above a weapon’s normal damage are never multiplied.

Thus, you include all modifiers that are just numbers, but do not include any extra rolled dice, like Sneak Attack. The only di(c)e that gets multiplied is the weapon’s base damage di(c)e.

For example, you Sneak Attack for +3d6 with a Rapier (1d8) and have Strength 14 (+2) and Weapon Specialization (Rapier) (+2), your normal attack is 1d8+4+3d6, and a Critical Hit is (1d8+4)×2+3d6.

Once per turn when you roll damage for a melee weapon attack, you can reroll the weapon’s damage dice and use either total.

Roll all of the attack’s damage dice twice and add them together.

Emphasis mine. Savage Attacker causes you to reroll all of the weapon's damage dice, so if you used it with a greatsword that deals 2d6, you would reroll both dice and choose one of the two sets of results. In the same way, if something (such as a critical hit) causes you to roll the weapon's damage dice more than once, then you have the option of re-rolling all of those dice and choosing which to use.