> 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 by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://ir0nstone.gitbook.io/notes/binexp/kernel/introduction.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. 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.