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Tuts 4 You

BIOS Disassembly Ninjutsu Uncovered

Teddy Rogers

About This File

For many years, there has been a myth among computer enthusiasts and practitioners that PC BIOS (Basic Input Output System) modification is a kind of black art and only a handful of people can do it or only the motherboard vendor can carry out such a task. On the contrary, this book will prove that with the right tools and approach, anyone can understand and modify the BIOS to suit their needs without the existence of its source code. It can be achieved by using a systematic approach to BIOS reverse engineering and modification. An advanced level of this modification technique is injecting a custom code to the BIOS binary.

There are many reasons to carry out BIOS reverse engineering and modification, from the fun of doing it to achieve higher clock speed in overclocking scenario, patching certain bug, injecting a custom security code into the BIOS, up to commercial interest in the embedded x86 BIOS market. The emergence of embedded x86 platform as consumer electronic products such as TV set-top boxes, telecom-related appliances and embedded x86 kiosks have raised the interest in BIOS reverse engineering and modification. In the coming years, these techniques will become even more important as the state of the art bus protocols have delegate a lot of their initialization task to the firmware, i.e. the BIOS. Thus, by understanding the techniques, one can dig the relevant firmware codes and understand the implementation of those protocols within the BIOS binary.

The main purpose of the BIOS is to initialize the system into execution environment suitable for the operating system. This task is getting more complex over the years, since x86 hardware evolves quite significantly. It’s one of the most dynamic computing platform on earth. Introduction of new chipsets happens once in 3 or at least 6 month. This event introduces a new code base for the silicon support routine within the BIOS. Nevertheless, the overall architecture of the BIOS is changing very slowly and the basic principle of the code inside the BIOS is preserved over generations of its code. However, there has been a quite significant change in the BIOS scene in the last few years, with the introduction of EFI (extensible Firmware Interface) by several major hardware vendors and with the growth in OpenBIOS project. With these advances in BIOS technology, it’s even getting more important to know systematically what lays within the BIOS.

In this book, the term BIOS has a much broader meaning than only motherboard BIOS, which is familiar to most of the reader. It also means the expansion ROM. The latter term is the official term used to refer to the firmware in the expansion cards within the PC, be it ISA, PCI or PCI Express.
So, what can you expect after reading this book? Understanding the BIOS will open a new frontier. You will be able to grasp how exactly the PC hardware works in its lowest level. Understanding contemporary BIOS will reveal the implementation of the latest bus protocol technology, i.e. HyperTransport and PCI-Express. In the software engineering front, you will be able to appreciate the application of compression technology in the BIOS. The most important of all, you will be able to carry out reverse engineering using advanced techniques and tools. You will be able to use the powerful IDA Pro disassembler efficiently. Some reader with advanced knowledge in hardware and software might even want to “borrow†some of the algorithm within the BIOS for their own purposes. In short, you will be on the same level as other BIOS code-diggers.

This book also presents a generic approach to PCI expansion ROM development using the widely available GNU tools. There will be no more myth in the BIOS and everyone will be able to learn from this state-of-the-art software technology for their own benefits.

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