Kernel Modules

Dynamically loadable code that extends the kernel

What kernel modules are

A kernel module is an ELF shared object loaded into the kernel at runtime. Modules: - Share the kernel's address space and run at ring 0 (full privilege) - Can export and use symbols from other modules or the core kernel - Are loaded by insmod/modprobe and removed by rmmod - Have an init function called on load and an exit function called on unload

Most device drivers, filesystems, and network protocols ship as modules.

Pages in this section

Page	What it covers
Writing and Loading Modules	module_init/exit, lifecycle, /proc/modules, debugging
Parameters, Symbols, and Kconfig	module_param, EXPORT_SYMBOL, Kconfig integration
Module Signing	CONFIG_MODULE_SIG, PKCS#7, key enrollment, verification flow
Kbuild Build System	Makefile structure, Kconfig, out-of-tree builds, cross-compilation
Module Loading Internals	load_module(), ELF parsing, relocation, symbol resolution, versioning
Dynamic Debug	pr_debug/dev_dbg, __dyndbg section, runtime control via debugfs
War Stories	CRC mismatches, signing failures, taint cascades, init use-after-free

Quick reference

# Load a module
insmod ./mymodule.ko
modprobe e1000e      # load with dependencies

# Unload
rmmod mymodule
modprobe -r e1000e   # remove with unused dependencies

# List loaded modules
lsmod

# Module info
modinfo e1000e

# Check kernel log for module messages
dmesg | tail -20