The meaning of the word "liberalism" in the english language is kind of distorted by american politics. I am assuming you mean **economic deregulation**. He was not totally in favor of it (not as much as anarcho-capitalists for instance), since it can impede social justice. Here is an easy way to explain his views on the matter, without any curves (the original text has some to illustrate his points).

A. Picture a society starting at a very egalistic repartition of revenue. Everyone has the same amount of wealth.

B. If you allow some moderate income differences, more resources are produced, and even the poorest can profit from these differences. This is desirable according to the second principle of justice (https://en.wikipedia.org/wiki/A_Theory_of_Justice#The_Second_Principle_of_Justice ).

C. If you allow even more income differences, you will, past a certain point :

- reduce the amount of wealth owned by the poorest members of the society, which is not desirable according to the second principle.

- reduce fairness of opportunity, not desirable according to the second principle.

Rawls aims to reach the middle point B. A liberal economy with measures such as progressive taxes in a closed economy is meant to reach situation B.

Note that, as explicitly mentioned in his book after the first principle of justice (https://en.wikipedia.org/wiki/A_Theory_of_Justice#The_First_Principle_of_Justice ), shareholding is not considered a basic liberty by Rawls. 

I think the confusion comes from the fact that Rawls views led him to support many positions from the USA democratic party, a.k.a. *the liberals*. This nickname comes from unrelated social issues (secularism, gay rights, ...), not economic liberalism. In the 2016 election, economic liberalism in its original meaning was represented by Gary Johnson.