How to hook system calls of my android app (non rooted device)

Question

I am trying to intercept all system calls made by my Android app on a non rooted device.

So every time my app writes/reads a file, I want to intercept the system call and encrypt/decrypt the stream for security purposes. The encryption part is no problem, but how do I intercept the system calls?

Because parts of the app are modules developed by third party providers of which I can not change the source code, there is no other way to make sure that data is stored securely.

Since I do not have root access I cannot access the address of the system call table as described here and I can not do this through an LKM module as well.

I would appreciate any suggestions, thanks.

Edit:

Ok I got the code link form Simone Margaritelli to work now! the reason why my code kept crashing is because i had to set the right memory access permisions:

uint32_t page_size = getpagesize();
uint32_t entry_page_start = reloc& (~(page_size - 1));
mprotect((uint32_t *)entry_page_start, page_size, PROT_READ | PROT_WRITE);

Answer 1

This is how you can hook syscalls on Android without root permissions ( only working for your own process of course, this is not system wide ).