elfloader: architecture-agnostic ELF file flattener for shellcode
elfloader
elfloader is a super simple loader for ELF files that generates a flat in-memory representation of the ELF.
Pair this with Rust and now you can write your shellcode in a proper, safe, high-level language. Any target that LLVM can target can be used, including custom target specifications for really exotic platforms and ABIs. Enjoy using things like u64s on 32-bit systems, bounds checked arrays, drop handling of allocations, etc 🙂
It simply concatenates all LOAD sections together, using zero padding if there are gaps, into one big flat file.
This file includes zero-initialization of .bss sections and thus can be used directly as a shellcode payload.
If you don’t want to waste time with fail-open linker scripts, this is probably a great way to go.
This doesn’t handle any relocations, it’s on you to make sure the original ELF is based at the address you want it to be at.
Internals
This tool doesn’t care about anything except for LOAD sections. It determines the endianness (little vs big) and bitness (32 vs 64) from the ELF header, and from there it creates a flat image based on program header virtual addresses (where it’s loaded), file size (number of initialized bytes) and mem size (size of actual memory region). The bytes are initialized from the file based on the offset and file size, and this is then extended with zeros until mem size (or truncated if mem size is smaller than file size).
These LOAD sections are then concatenated together with zero-byte padding for gaps.
This is designed to be incredibly simple, and agnostic to the ELF input. It could be an executable, object file, shared object, core dump, etc, doesn’t really care. It’ll simply give you the flat representation of the memory, nothing more.
This allows you to turn any ELF into shellcode, or a simpler file format that is easier to load in hard-to-reach areas, like embedded devices. Personally, I developed this for my MIPS NT 4.0 loader which allows me to run Rust code.
Install
git clone https://github.com/gamozolabs/elfloader.git
cargo install –path .
Use
FELF0001 format
This tool by default generates a FELF file format. This is a Falk ELF. This is a simple file format:
FELF0001 – Magic header
entry – 64-bit little endian integer of the entry point address
base – 64-bit little endian integer of the base address to load the image
<image> – Rest of the file is the raw image, to be loaded at `base` and jumped
into at `entry`
Source: https://github.com/gamozolabs/
