Book Image

Learning Linux Binary Analysis

By : Ryan "elfmaster" O'Neill
Book Image

Learning Linux Binary Analysis

By: Ryan "elfmaster" O'Neill

Overview of this book

Learning Linux Binary Analysis is packed with knowledge and code that will teach you the inner workings of the ELF format, and the methods used by hackers and security analysts for virus analysis, binary patching, software protection and more. This book will start by taking you through UNIX/Linux object utilities, and will move on to teaching you all about the ELF specimen. You will learn about process tracing, and will explore the different types of Linux and UNIX viruses, and how you can make use of ELF Virus Technology to deal with them. The latter half of the book discusses the usage of Kprobe instrumentation for kernel hacking, code patching, and debugging. You will discover how to detect and disinfect kernel-mode rootkits, and move on to analyze static code. Finally, you will be walked through complex userspace memory infection analysis. This book will lead you into territory that is uncharted even by some experts; right into the world of the computer hacker.
Table of Contents (17 chapters)
Learning Linux Binary Analysis
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

vmlinux and .altinstructions patching


In my opinion, the single most effective method of rootkit detection can be summed up by verifying the code integrity of the kernel in the memory—in other words, comparing the code in the kernel memory against the expected code. But what can we compare kernel memory code against? Well, why not vmlinux? This was an approach that I originally explored in 2008. Knowing that an ELF executable's text segment does not change from disk to memory, unless it's some weird self-modifying binary, which the kernel is not… or is it? I quickly ran into trouble and was finding all sorts of code discrepancies between the kernel memory text segment and the vmlinux text segment. This was baffling at first since I had no kernel rootkits installed during these tests. After examining some of the ELF sections in vmlinux, however, I quickly saw some areas that caught my attention:

$ readelf -S vmlinux | grep alt
  [23] .altinstructions  PROGBITS         ffffffff81e64528  01264528...