Introduction To ARM Assembly Basics [The Weakest Link?]

Introduction To ARM Assembly Basics

The latest security fails by Intel and Microsoft capture media and blog headlines but ARM devices are more numerous.

ARM devices, like a Windows server in an unlocked closet, may be the weakest link in your next target.

From the webpage:

Welcome to this tutorial series on ARM assembly basics. This is the preparation for the followup tutorial series on ARM exploit development. Before we can dive into creating ARM shellcode and build ROP chains, we need to cover some ARM Assembly basics first.

The following topics will be covered step by step:

ARM Assembly Basics Tutorial Series:
Part 1: Introduction to ARM Assembly
Part 2: Data Types Registers
Part 3: ARM Instruction Set
Part 4: Memory Instructions: Loading and Storing Data
Part 5: Load and Store Multiple
Part 6: Conditional Execution and Branching
Part 7: Stack and Functions

To follow along with the examples, you will need an ARM based lab environment. If you don’t have an ARM device (like Raspberry Pi), you can set up your own lab environment in a Virtual Machine using QEMU and the Raspberry Pi distro by following this tutorial. If you are not familiar with basic debugging with GDB, you can get the basics in this tutorial. In this tutorial, the focus will be on ARM 32-bit, and the examples are compiled on an ARMv6.

Why ARM?

This tutorial is generally for people who want to learn the basics of ARM assembly. Especially for those of you who are interested in exploit writing on the ARM platform. You might have already noticed that ARM processors are everywhere around you. When I look around me, I can count far more devices that feature an ARM processor in my house than Intel processors. This includes phones, routers, and not to forget the IoT devices that seem to explode in sales these days. That said, the ARM processor has become one of the most widespread CPU cores in the world. Which brings us to the fact that like PCs, IoT devices are susceptible to improper input validation abuse such as buffer overflows. Given the widespread usage of ARM based devices and the potential for misuse, attacks on these devices have become much more common.

Yet, we have more experts specialized in x86 security research than we have for ARM, although ARM assembly language is perhaps the easiest assembly language in widespread use. So, why aren’t more people focusing on ARM? Perhaps because there are more learning resources out there covering exploitation on Intel than there are for ARM. Just think about the great tutorials on Intel x86 Exploit writing by Fuzzy Security or the Corelan Team – Guidelines like these help people interested in this specific area to get practical knowledge and the inspiration to learn beyond what is covered in those tutorials. If you are interested in x86 exploit writing, the Corelan and Fuzzysec tutorials are your perfect starting point. In this tutorial series here, we will focus on assembly basics and exploit writing on ARM.

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Enjoy!

PS: She recently posted an really cool cheatsheet: Assembly Basics Cheatsheet. I’m going to use it to lobby (myself) for a pair of 32″ monitors so I can enlarge it on one screen and have a non-scrolling display. (Suggestions on the monitors?)

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