GitHub - Mockapapella/mov-http-server: This repo implements an http server using only MOV instructions

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M/o/Vfuscator HTTP Server

A simple HTTP server that uses only the mov instruction, compiled with the M/o/Vfuscator. The server runs on port 8080 and returns "Hello, world". The original server was modified into a movcc compatible version with the help of o1.

Setup

  1. Clone movfuscator
git clone https://github.com/xoreaxeaxeax/movfuscator.git
  1. Install dependencies:
sudo apt update
sudo apt install build-essential git bison flex libgmp3-dev libmpfr-dev libmpc-dev texinfo
  1. Build the compiler:
cd movfuscator
./build.sh
  1. Compile the server:
cd ..
movfuscator/build/movcc -o server_mov_compatible server_mov_compatible.c
  1. Run the server:
  1. Test it:
curl http://localhost:8080/

You should see: <html>hello, world</html>

You can view the instructions using objdump:

objdump -d -Mintel server_mov_compatible

Technical Details

Implementations and Key Decisions Differing from the Original Code

Custom Network Structures and Constants

  • Reason: The M/o/Vfuscator's movcc compiler cannot handle certain standard headers due to 64-bit constants and constructs.
  • Implementation: Defined minimal versions of struct sockaddr_in, struct in_addr, and constants like AF_INET, SOCK_STREAM, and INADDR_ANY directly in server.c.

Custom Byte Order Functions

  • Reason: Functions like htons and ntohs are either unsupported or rely on headers that cause issues.
  • Implementation: Created my_htons and my_ntohs functions to handle byte order conversions.

Custom IP Address Conversion Function

  • Reason: The standard inet_ntoa function depends on headers and implementations not compatible with movcc.
  • Implementation: Wrote my_inet_ntoa to convert an IP address to a dotted-decimal string without external dependencies.

Manual HTTP Request Parsing

  • Reason: Functions like sscanf may not be fully supported or could introduce complications.
  • Implementation: Implemented manual parsing of the HTTP request to extract the method, URI, and version.

Compliance with C89/C90 Standards

  • Reason: The movcc compiler adheres to the older C89/C90 standards, requiring variable declarations at the beginning of blocks.
  • Implementation: Ensured all variables are declared at the start of their respective blocks.

Avoidance of Problematic Headers

  • Reason: Inclusion of headers like <arpa/inet.h> and <netinet/in.h> caused compilation errors due to 64-bit constants and other unsupported features.
  • Implementation: Excluded these headers and provided necessary functionality through custom code.

Simplification of Code

  • Reason: To minimize compatibility issues with the movcc compiler.
  • Implementation: Removed unnecessary code and kept the implementation as straightforward as possible.

Troubleshooting

If the server won't start:

  1. Check if port 8080 is free:
    • Use sudo lsof -i -P -n | grep LISTEN to see if another service is using the port.
  2. Try a different port:
    • Edit #define PORT 8080 in server.c to a different port (e.g., 8081), recompile, and run the server again.
  3. Verify localhost configuration:
    • Ensure that localhost or 127.0.0.1 is properly set up in your /etc/hosts file.
  4. Check firewall settings:
    • Your firewall might be blocking connections to the port. Adjust the settings accordingly.

If compilation fails:

  1. Verify movcc path:
    • Ensure you are using the correct path to movcc: movfuscator/build/movcc.
  2. Ensure all dependencies are installed:
    • Revisit the installation step for dependencies to confirm everything is installed.
  3. Avoid external headers:
    • Do not include additional headers that may introduce incompatibilities.

Additional Notes

Original Implementation Differences

The original server code relied on standard networking headers and functions, such as <arpa/inet.h>, <netinet/in.h>, htons, ntohs, inet_ntoa, and sscanf. These were replaced or reimplemented to ensure compatibility with the M/o/Vfuscator.

Custom Implementations

By providing custom definitions and functions, we eliminated the need for headers and functions that caused compilation issues, allowing us to successfully compile the server with movcc.

Why These Changes Were Necessary

The M/o/Vfuscator's movcc compiler has limitations due to its adherence to older C standards and inability to handle certain constructs, especially those involving 64-bit constants or complex library functions. Adjusting the code accordingly was essential to achieve a successful compilation.

Testing the Server

After starting the server, you can open a web browser and navigate to http://localhost:8080/ to see the "Hello, world" message.

Stopping the Server

Since the server runs in an infinite loop, you can stop it by pressing Ctrl + C in the terminal where it's running.

Credit

Huge credit to both Bruins Slot for his tutorial on implementing an http server from scratch and Christopher Domas who created the original movfuscator.