memfd-runner

A minimal Linux library for executing in-memory ELF files using memfd_create and execve.

Overview

memfd-runner provides a simple interface to load and execute ELF binaries directly from memory without writing them to disk. It uses Linux's memfd_create system call to create an anonymous file in memory, writes the ELF data to it, then executes it via the /proc/self/fd/ interface.

Features

• Minimal - <400 lines of code, 1 dependency (syscaller)
• Two execution modes - fork child process or replace current process
• no_std - works in embedded and kernel environments

Platform Support

• Linux only - requires memfd_create system call (Linux 3.17+)
• x86_64 - tested on x86_64 architecture

Installation

cargo add mdmfd-runner

Or add this to your Cargo.toml:

[dependencies]
memfd-runner = "0.1.0"

Quick Start

Simple Execution (Fork Mode)

use memfd_runner::run;

// Read an ELF binary
let elf_bytes = std::fs::read("/usr/bin/echo").unwrap();

// Execute it and get the exit code
let exit_code = run(&elf_bytes).unwrap();
println!("Process exited with code: {}", exit_code);

Replace Current Process

use memfd_runner::{run_with_options, RunOptions};

let elf_bytes = std::fs::read("/usr/bin/uname").unwrap();
let options = RunOptions::new().with_replace(true);

// This will replace the current process - does not return on success
run_with_options(&elf_bytes, options).unwrap();

Error Handling

use memfd_runner::{run, RunError};

let invalid_data = b"not an elf file";
match run(invalid_data) {
    Ok(exit_code) => println!("Success: {}", exit_code),
    Err(RunError::InvalidElfFormat) => println!("Invalid ELF format"),
    ...
}

API Reference

Functions

• run<B: AsRef<[u8]>>(bytes: B) -> Result<i32, RunError>

  • Execute ELF bytes in fork mode, returns child exit code

• run_with_options<B: AsRef<[u8]>>(bytes: B, options: RunOptions) -> Result<i32, RunError>

  • Execute ELF bytes with custom options

Types

• RunOptions - Configuration for execution

  • new() - Create default options (fork mode)
  • with_replace(bool) - Set replace mode (true = replace process, false = fork child)

• RunError - Error types with context

  • FdCreationFailed(i32) - Failed to create memory file descriptor
  • BytesNotWritten(usize, usize) - Write operation failed (written, expected)
  • ExecError(i32) - execve system call failed
  • ForkError(i32) - fork system call failed
  • WaitError(i32) - wait4 system call failed
  • InvalidElfFormat - ELF validation failed

How It Works

1. Create Memory FD: Uses memfd_create() to create an anonymous file in memory
2. Write Data: Writes the ELF bytes to the memory file descriptor
3. Execute: Uses execve() with /proc/self/fd/<fd> path to execute the in-memory file
4. Wait for Child: In fork mode, waits for child process and returns exit code

⚠️ Limitations: Very basic ELF validation only - complex validation should be done by caller

Examples

See the examples/ directory for complete examples:

• example.rs - Basic usage demonstration

Development

Building

cargo build

Testing

cargo test

Linting

cargo check
cargo clippy

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request

License

This project is licensed under the MIT License - see the LICENSE file for details.

Changelog

0.1.0

• Initial release
• Basic memfd_create + execve functionality
• Fork and replace execution modes
• ELF validation
• Comprehensive error handling