SGX only guarantees the isolated memory region remains isolated. It doesn’t guarantee the code running in it is secure or even leak-free. Microsoft Research has

SGX only guarantees the isolated memory region remains isolated. It doesn’t guarantee the code running in it is secure or even leak-free. Microsoft Research has studies this and release a compiler for making stronger claims about code running inside the enclave but I think this is still very much an open problem. You will always want layers of security and even then security is an illusion .... there will always be a way, just with different costs to exploit and thus risk/reward frontier.