> For the complete documentation index, see [llms.txt](https://ir0nstone.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ir0nstone.gitbook.io/notes/binexp/kernel/introduction.md).

# Introduction

The kernel is the program at the heart of the Operating System. It is responsible for controlling every aspect of the computer, from the nature of syscalls to the integration between software and hardware. As such, exploiting the kernel can lead to some incredibly dangerous bugs.

In the context of CTFs, Linux kernel exploitation often involves the exploitation of kernel **modules**. This is an integral feature of Linux that allows users to extend the kernel with their own code, adding additional features.

You can find an excellent introduction to Kernel Drivers and Modules by LiveOverflow [here](https://www.youtube.com/watch?v=juGNPLdjLH4), and I recommend it highly.

### Kernel Modules

Kernel Modules are written in C and compiled to a `.ko` (**K**ernel **O**bject) format. Most kernel modules are compiled for a specific version kernel version (which can be checked with `uname -r`, my Xenial Xerus is `4.15.0-128-generic`). We can load and unload these modules using the `insmod` and `rmmod` commands respectively. Kernel modules are often loaded into `/dev/*` or `/proc/`. There are 3 main module types: **Char**, **Block** and **Network**.

#### Char Modules

*Char* Modules are deceptively simple. Essentially, you can access them as a **stream of bytes** - just like a file - using syscalls such as `open`. In this way, they're virtually almost dynamic files (at a super basic level), as the values read and written can be changed.

Examples of Char modules include `/dev/random`.

{% hint style="info" %}
I'll be using the term *module* and *device* interchangeably. As far as I can tell, they are the same, but please let me know if I'm wrong!
{% endhint %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://ir0nstone.gitbook.io/notes/binexp/kernel/introduction.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.