Undo,Redo and Buffer cache buffers all in SHARED POOL !!!!
I had read about Undo and redo buffers being preset in the shared pool for version > 10g , but today i came to know that even buffer cache can be stored inside shared pool.Below are some links that you can go through
Undo and Redo Buffers in Shared Pool :- http://blog.aristadba.com/?p=17
Buffer Cache Buffers in Shared Pool :- http://blog.tanelpoder.com/2009/09/09/kgh-no-access-allocations-in-vsgastat-buffer-cache-within-shared-pool/
For some observations you can go through