snippets/c/linux_loader_poc

Proof-of-concept custom loaders in Linux

This is a proof-of-concept to show different methods to load executables in the Linux kernel with our own loaders / linkers / interpreters.

Methods

1. binfmt_misc

We use a kernel module called binfmt_misc to register our own binary format in the Linux kernel.

The loader will be called in userspace.

See: https://www.kernel.org/doc/Documentation/binfmt_misc.txt

See: demo_binfmt_misc in Makefile

2. ELF Interpreter section (INTERP)

Every dynamically linked ELF executable contains a special section called .interp.

In case the Linux kernel sees such a section, I will load the interpreter instead. Afterwards, it is the task of the interpreter (usually ld-linux.so) to load all dependencies and do the final relocation.

See: demo_interpreter in the Makefile

3. Custom kernel module

We use the binfmt subsystem of the Linux kernel to implement our own format.

A good example is the loader for the script she-bangs (#!/bin/bash et al):

https://github.com/torvalds/linux/blob/master/fs/binfmt_script.c

Credits

Steffen Vogel post@steffenvogel.de