To clarify things a bit more - in EntityFramework the DbContext  is a unit-of-work, and IDbSet<T> is a repository. They are abstractions and by wrapping it with your own, you're making an abstraction over an abstraction, and in my opinion you gain nothing but complexity.

Please take a look at the following post:

http://rob.conery.io/2014/03/04/repositories-and-unitofwork-are-not-a-good-idea/

That being said, to answer your question - your business layer will have a reference to your EF context or a repository you build yourself.

Additionally, I recommend you use DTOs vs. returning the Entities directly.