Book Image

Linux Kernel Programming

By : Kaiwan N. Billimoria
Book Image

Linux Kernel Programming

By: Kaiwan N. Billimoria

Overview of this book

Linux Kernel Programming is a comprehensive introduction for those new to Linux kernel and module development. This easy-to-follow guide will have you up and running with writing kernel code in next-to-no time. This book uses the latest 5.4 Long-Term Support (LTS) Linux kernel, which will be maintained from November 2019 through to December 2025. By working with the 5.4 LTS kernel throughout the book, you can be confident that your knowledge will continue to be valid for years to come. You’ll start the journey by learning how to build the kernel from the source. Next, you’ll write your first kernel module using the powerful Loadable Kernel Module (LKM) framework. The following chapters will cover key kernel internals topics including Linux kernel architecture, memory management, and CPU scheduling. During the course of this book, you’ll delve into the fairly complex topic of concurrency within the kernel, understand the issues it can cause, and learn how they can be addressed with various locking technologies (mutexes, spinlocks, atomic, and refcount operators). You’ll also benefit from more advanced material on cache effects, a primer on lock-free techniques within the kernel, deadlock avoidance (with lockdep), and kernel lock debugging techniques. By the end of this kernel book, you’ll have a detailed understanding of the fundamentals of writing Linux kernel module code for real-world projects and products.
Table of Contents (19 chapters)
1
Section 1: The Basics
6
Writing Your First Kernel Module - LKMs Part 2
7
Section 2: Understanding and Working with the Kernel
10
Kernel Memory Allocation for Module Authors - Part 1
11
Kernel Memory Allocation for Module Authors - Part 2
14
Section 3: Delving Deeper
17
About Packt

User-mode ASLR

User-mode ASLR is usually what is meant by the term ASLR. It being enabled implies this protection to be available on the user space mapping of every process. Effectively, ASLR being enabled implies that the absolute memory map of user-mode processes will vary every time they're run.

ASLR has been supported on Linux for a very long time (since 2005 on 2.6.12). The kernel has a tunable pseudo-file within procfs, to query and set (as root) the ASLR status; here it is: /proc/sys/kernel/randomize_va_space.

It can have three possible values; the three values and their meaning are shown in the following table:

Tunable value Interpretation of this value in /proc/sys/kernel/randomize_va_space
0 (User mode) ASLR turned OFF; or can be turned off by passing the kernel parameter norandmaps at boot.
1 (User mode) ASLR is ON: mmap(2) based allocations, the stack, and the vDSO page is randomized. It also implies that shared library load locations and shared...