This is a collection of documentation for angr. By reading this, you'll become an angr pro and will be able to fold binaries to your whim.
angr is a multi-architecture binary analysis platform, with the capability to perform dynamic symbolic execution (like Mayhem, KLEE, etc) and various static analyses on binaries. Several challenges must be overcome to do this. They are, roughly:
- Loading a binary into the analysis program.
- Translating a binary into an intermediate representation (IR).
- Translating that IR into a semantic representation (i.e., what it does, not just what it is).
- Performing the actual analysis. This could be:
- A full-program static analysis (i.e., type inference, program slicing).
- A symbolic exploration of the program's state space (i.e., "Can we execute it until we find an overflow?").
- Some combination of the above (i.e., "Let's execute only program slices that lead to a memory write, to find an overflow.")
angr has components that meet all of these challenges. This document will explain how each one works, and how they can all be used to accomplish your evil goals.
We've tried to make using angr as pain-free as possible. Our goal is to create the most user-friendly binary analysis platform, allowing one to simply start up iPython and easily perform extremely complex binary analyses with a couple of commands. That being said, binary analysis is complex, which makes angr complex. We've tried to make life easier by providing this documentation, split into several sections for easier consumption.
Before angr can be used, it must be installed.
Ideally, you should just be able to say pip install angr, but failing that, you should be
able to install the following repositories (and the dependencies listed in their requirements.txt files)
from http://github.com/angr:
- angr
- simuvex
- claripy
- cle
- pyvex
- archinfo
After angr is installed, you can load a binary for analysis. This process, and the angr component that powers it (called CLE) is described here.
angr uses an intermediate representation (specificaly, VEX) to enable it to run analyses on binaries of different architectures. This IR is described here
Constraint solving and other computational needs are provided by an angr sub-module called Claripy. Most users of angr will not need to know anything about Claripy, but documentation is provided in case it is needed. Claripy is detailed here.
angr provides an interface to the emulated machine state. Understanding this is critical to successfully using angr. It is detailed here.
Programs can be analyzed in terms of the possible path that execution takes through them. angr exposes information about what the paths execute and do. This section gives an overview of how to use this capability of angr.
A powerful feature of angr is the ability to represent basic blocks in terms of their effects on a program state. In other words, angr can reason about what basic blocks do, not just what they are. This is accomplished by a module named SimuVEX, further described here.
angr provides a capable symbolc execution engine. The interface to this engine, and how to use it, is described here.
All of the above components come together to enable complex, full-program analyses to be easily runnable in angr. The mechanism for running and writing these analyses is detailed here.
angr comes with the ability to perform distributed analysis, with directions here.
We've written some examples for using angr! You can read more here.
We've put together some guidelines so that we can keep the codebase in good shape!
We try to get as close as the PEP8 code convention as is reasonable without being dumb. If you use Vim, the python-mode plugin does all you need. You can also manually configure vim to adopt this behavior.
Most importantly, please consider the following when writing code as part of angr:
- Try to use attribute access (see the
@propertydecorator) instead of getters and setters wherever you can. This isn't Java, and attributes enable tab completion in iPython. That being said, be reasonable: attributes should be fast. A rule of thumb is that if something could require a constraint solve, it should not be an attribute. - Use our pylintrc. It's fairly permissive, but our CI server will fail your builds if pylint complains under those settings.
- DO NOT, under ANY circumstances,
raise Exceptionorassert False. Use the right exception type. If there isn't a correct exception type, subclass the core exception of the module that you're working in (i.e. AngrError in angr, SimError in SimuVEX, etc) and raise that. We catch, and properly handle, the right types of errors in the right places, but AssertionError and Exception are not handled anywhere and force-terminate analyses. - Avoid tabs, use space indentation instead. Even though it's wrong, the de-facto standard is 4 spaces. It is a good idea to adopt this from the beginning, as merging code that mixes both tab and space indentation is awful.
- Avoid super long lines. It's okay to have longer lines, but keep in mind that long lines are harder to read and should be avoided. Let's try to stick to 120 characters.
- Avoid extremely long functions, it is often better to break them up into smaller functions.
- Prefer
_to__for private members (so that we can access them when debugging). You might not think that anyone has a need to call a given function, but trust us, you're wrong. - Document your code. Every class definition and public function definition should have some description of:
- What it does.
- What are the type and the meaning of the parameters.
- What it returns.
- If you're pushing a new feature, and it is not accompanied by a testcase, it will be broken in very short order. Please write testcases for your stuff.
We've collected miscellaneous questions about angr, and answers to them, in a FAQ.
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