Most of the kindnesses that Baba shows Amir take place once they have reached the United States. Their relationship before that is problematic, with each frequently disappointed in the other.
When Amir and Soraya become engaged and they are on their way to the house of the General, Baba tells Amir, "You look khoshteep" (166), which means "handsome." This was a kindness because Amir was concerned about his appearance as he prepared to visit the family he was marrying into.
To pay for the wedding, "Baba spent $35,000, nearly the balance of his life savings..." (169). This was certainly a kindness!
The night Baba died, Soroya and Amir helped him get into bed, and Amir says, "He asked us to lean in, gave each of us a kiss" (173). This was more than a kindness; it was like a blessing on Amir, on Soroya, and on their marriage.
That Amir and Baba grew to appreciate one another and grow close when they got to America was an important part of Amir's growth and really part of his redemption for his failures in the past. I am sure there are other example's of Baba's kindness in the story.
Good luck to you!