SyscallAdder

Linux kernel module that can be used to add custom system call in a more user-friendly way.

This module will add 2 system call:

1. syscall_adder((void *)custom_syscall_addr, char *syscall_name, int num_parameters): will check if there is a free entry on the syscall table and if so, the syscall will be inserted. There will be inserted a MACRO in a file (located at ~/custom_syscall_macros.h). This macro, when imported in the user c file where the cusom syscall is used, will make possible calling the new syscall like: custom_syscall(...).

2. syscall_remover(int custom_syscall_name): This system call will simply delete a custom system call inserted previously.

Usage

Fist of all you have to download and install the syscall_adder module:

1. git clone https://github.com/x-Ultra/SyscallAdder
2. cd SyscallAdder
3. Edit #define MACRO_DIR "/dir/to/macro/file" at line 35 of syscalladder.c
4. sudo ./install
5. To uninstall sudo ./uninstall </dir/to/macro/file>

Then, to add a new system call:

1. Open the 'your_syscall.c' file in 'template' folder
2. Edit the template as you need
3. While adding a new syscall remember to use an integer variable to maintain the index of the added syscall (line 15), to use in the removing procedure.
4. Rename the your_syscall.c as you want
5. To install your module (and your system calls): sudo ./insert_syscall
6. To remove: sudo ./remove_syscall

To use you new systemcall just import the macro file /dir/to/macro/file/custom_syscall_macros.h into your user C file.

The MACRO file

Let's suppose to add the system call 'my_sys(int arg1)', and let's suppose that the syscall_adder will insert it in the (system call table) index 187. The macro file will look like that:

//187
#define my_sys(arg1) syscall(187, arg1)
//end

This means that the syscall_adder has to know the number of parameters in order to create the appropiate macro. That's it.