alt Hacker NewsYou may run afoul of DCMA rules around circumventing copy protection measures, and you are most likely going to be violating the EULA on any recent games. But you aren't necessarily violating any copyrights - several high-profile cases in the US have been fought about this, such as Sony vs Connectix, and its generally fallen on the side of reverse-engineering for interoperability being within the bounds of fair use
(as always, IANAL)
Computer Associates International, Inc. v. Altai, Inc. establishes the Abstraction-Filtration-Comparison test for determining if a program is infringing on another program. Reverse engineered code of a nontrivial portion of the original program will have substantial similarity to the original program and will fail this test.
Interoperability falls under what gets filtered out in the filtration step of the test.