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Showing posts with the label Embedded Linux

Reversing a bare bones Raspberry Pi Kernel : Branching To the Kernel

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I lost the first version of this post because of problem in blogger's auto-save function.

Anyway so if you want to get your own raspberry pi os kernel going, I share some cool posts on that in here and expand on them by unpacking some of the assembler code essentially reverse engineering it or "unrolling" the os. 
Setting up your Development Environment I think the explanation of the 'Roll your own Rapsberry Pi Os' at https://jsandler18.github.io/ pretty much sorts this out I can at least do the favor of confirming that this persons advice definitely does the job so check it out.  The post also discusses the background of why we need certain files in the project for instance like the linker scripts and kernel.c files. As a short summary here's the basic work flow:

1 - Write a linker script This is to make sure the compiler can recombined the boot.S and kernel.c parts 2 - Write a boot.S This file is to initialize the run time for your kernel and branch into i…

[Reverse Engineering Primer] Unpacking cramfs firmware file systems

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Reverse engineering firmware from the point of view of an attacker involves levering as much as possible what is accessible from the physical board. Of course the classic question this strives to answer is, if someone gets hold of my board what could go wrong? Reverse engineering some devices in the wild often exposes security keys, default passwords and other forms of security failures that can expose an unfair escalation of privilege or perhaps also allow a complete take over of the device right down to boot loader level - all of this sometimes also possibly learned by analyzing the firmware.

I'm going to talk about some of the more basic skill in getting toward exposing the code and other sensitive artifacts used by the device. Before you can find remote code execs and admin auth by pass vulns you need to get to grips with firmware image formats and embedded file systems.

Setting up the environment 
Before getting super in depth and writing our own file format parsers, machine …