🔎 Linux Kernel Module - Introduction

<time datetime="2022-12-18 10:50:42 +0200 +0200">18 December 2022</time>·332 words·2 mins· 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"> <path fill="currentColor" d="M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z"/></svg> · 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"> <path fill="currentColor" d="M47.6 300.4L228.3 469.1c7.5 7 17.4 10.9 27.7 10.9s20.2-3.9 27.7-10.9L464.4 300.4c30.4-28.3 47.6-68 47.6-109.5v-5.8c0-69.9-50.5-129.5-119.4-141C347 36.5 300.6 51.4 268 84L256 96 244 84c-32.6-32.6-79-47.5-124.6-39.9C50.5 55.6 0 115.2 0 185.1v5.8c0 41.5 17.2 81.2 47.6 109.5z"/></svg> · <button id="likes_button" class="rounded-md border border-primary-400 px-1 py-[1px] text-xs font-normal text-primary-700 dark:border-primary-600 dark:text-primary-400" onclick="process_article()"> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"> <path fill="currentColor" d="M47.6 300.4L228.3 469.1c7.5 7 17.4 10.9 27.7 10.9s20.2-3.9 27.7-10.9L464.4 300.4c30.4-28.3 47.6-68 47.6-109.5v-5.8c0-69.9-50.5-129.5-119.4-141C347 36.5 300.6 51.4 268 84L256 96 244 84c-32.6-32.6-79-47.5-124.6-39.9C50.5 55.6 0 115.2 0 185.1v5.8c0 41.5 17.2 81.2 47.6 109.5z"/></svg> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"> <path fill="currentColor" d="M244 84L255.1 96L267.1 84.02C300.6 51.37 347 36.51 392.6 44.1C461.5 55.58 512 115.2 512 185.1V190.9C512 232.4 494.8 272.1 464.4 300.4L283.7 469.1C276.2 476.1 266.3 480 256 480C245.7 480 235.8 476.1 228.3 469.1L47.59 300.4C17.23 272.1 0 232.4 0 190.9V185.1C0 115.2 50.52 55.58 119.4 44.1C164.1 36.51 211.4 51.37 244 84C243.1 84 244 84.01 244 84L244 84zM255.1 163.9L210.1 117.1C188.4 96.28 157.6 86.4 127.3 91.44C81.55 99.07 48 138.7 48 185.1V190.9C48 219.1 59.71 246.1 80.34 265.3L256 429.3L431.7 265.3C452.3 246.1 464 219.1 464 190.9V185.1C464 138.7 430.4 99.07 384.7 91.44C354.4 86.4 323.6 96.28 301.9 117.1L255.1 163.9z"/></svg>  Like </button> · <a href="https://github.com/OxNinja/blog" class="text-lg hover:text-primary-500" rel="noopener noreferrer" target="_blank" title="Edit content" > <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path fill="currentColor" d="M490.3 40.4C512.2 62.27 512.2 97.73 490.3 119.6L460.3 149.7L362.3 51.72L392.4 21.66C414.3-.2135 449.7-.2135 471.6 21.66L490.3 40.4zM172.4 241.7L339.7 74.34L437.7 172.3L270.3 339.6C264.2 345.8 256.7 350.4 248.4 353.2L159.6 382.8C150.1 385.6 141.5 383.4 135 376.1C128.6 370.5 126.4 361 129.2 352.4L158.8 263.6C161.6 255.3 166.2 247.8 172.4 241.7V241.7zM192 63.1C209.7 63.1 224 78.33 224 95.1C224 113.7 209.7 127.1 192 127.1H96C78.33 127.1 64 142.3 64 159.1V416C64 433.7 78.33 448 96 448H352C369.7 448 384 433.7 384 416V319.1C384 302.3 398.3 287.1 416 287.1C433.7 287.1 448 302.3 448 319.1V416C448 469 405 512 352 512H96C42.98 512 0 469 0 416V159.1C0 106.1 42.98 63.1 96 63.1H192z"/></svg> </a >

LKM c lkm low-level

Author

0xNinja

mov al, 11

Table of Contents

LKM - This article is part of a series.

Part 1: This Article

How to create a basic Linux Kernel Module.

A LKM is like a .so library, and can run kernel-land.

Writting your own kernel module will help you to understand how the system works and make you think about mallocing in the kernel twice before running the code.

Code #

Here is the bare minimum you have to code to get a working LKM:

 1#include <linux/module.h>
 2#include <linux/kernel.h>
 3
 4// Specify module licence, GPL to not taint the kernel
 5MODULE_LICENSE("GPL");
 6
 7// Called on module load
 8int init_module(void) {
 9  printk(KERN_INFO "MODULE loaded!\n");
10  return 0;
11}
12
13// Called on module unload
14void cleanup_module(void) {
15  printk(KERN_INFO "MODULE unloaded!\n");
16}

Compile #

The Makefile I use for my modules:

 1obj-m += my_module.o
 2
 3all:
 4    sudo make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
 5
 6install:
 7    sudo insmod ./my_module.ko
 8
 9uninstall:
10    sudo rmmod my_module
11
12clean:
13    sudo make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Then just run make. A new my_module.ko should be here, this is your kernel module.

Install #

1sudo insmod ./my_module.ko
2# or
3make install

In dmesg you should have a new line containing MODULE loaded!. Your module is loaded in the kernel.

Uninstall #

1sudo rmmod my_module
2# or
3make uninstall

In dmesg you should have a new line containing MODULE unloaded!. Your module is deleted form the kernel.

MISC #

dmesg -C will clear the dmesg buffer
watch 'dmesg | grep MODULE' will append the new messages of the module so you don’t have to re-run the command

Afterwords #

Starting to create a kernel module is pretty easy, you just have to be careful with the functions you call and how you code them. There are a lot of specific functions for the kernel only, and you must check them out before using them.

In the future I will discuss more about the internals of Linux and why using a kernel module is insanely powerfull and at the same time a pain to code.

LKM - This article is part of a series.

Part 1: This Article

Draft

🔎 Creating a VM for fun - Part 2: C

<time datetime="2022-05-09 10:39:42 +0200 +0200">9 May 2022</time>·1225 words·6 mins· 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"> <path fill="currentColor" d="M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z"/></svg> · 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"> <path fill="currentColor" d="M47.6 300.4L228.3 469.1c7.5 7 17.4 10.9 27.7 10.9s20.2-3.9 27.7-10.9L464.4 300.4c30.4-28.3 47.6-68 47.6-109.5v-5.8c0-69.9-50.5-129.5-119.4-141C347 36.5 300.6 51.4 268 84L256 96 244 84c-32.6-32.6-79-47.5-124.6-39.9C50.5 55.6 0 115.2 0 185.1v5.8c0 41.5 17.2 81.2 47.6 109.5z"/></svg>

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🏌️ Binary golfing - Introduction

<time datetime="2022-04-15 16:00:00 +0000 UTC">15 April 2022</time>·711 words·4 mins· 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"> <path fill="currentColor" d="M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z"/></svg> · 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"> <path fill="currentColor" d="M47.6 300.4L228.3 469.1c7.5 7 17.4 10.9 27.7 10.9s20.2-3.9 27.7-10.9L464.4 300.4c30.4-28.3 47.6-68 47.6-109.5v-5.8c0-69.9-50.5-129.5-119.4-141C347 36.5 300.6 51.4 268 84L256 96 244 84c-32.6-32.6-79-47.5-124.6-39.9C50.5 55.6 0 115.2 0 185.1v5.8c0 41.5 17.2 81.2 47.6 109.5z"/></svg>

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🏌️ BGGP3 - How to crash a famous JS engine for fun

<time datetime="2022-07-18 19:00:00 +0000 UTC">18 July 2022</time>·1571 words·8 mins· 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"> <path fill="currentColor" d="M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z"/></svg> · 0 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"> <path fill="currentColor" d="M47.6 300.4L228.3 469.1c7.5 7 17.4 10.9 27.7 10.9s20.2-3.9 27.7-10.9L464.4 300.4c30.4-28.3 47.6-68 47.6-109.5v-5.8c0-69.9-50.5-129.5-119.4-141C347 36.5 300.6 51.4 268 84L256 96 244 84c-32.6-32.6-79-47.5-124.6-39.9C50.5 55.6 0 115.2 0 185.1v5.8c0 41.5 17.2 81.2 47.6 109.5z"/></svg>

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