Implementing Linux System Call using LKM

问题

I was trying to add a new System Call to linux kernel 3.2.x. While searching for useful reference material over the internet i had an impression that implementing system call as a loadable module is not possible as in SO question Is it possible to add a system call via a LKM?

I found another link which says this "There is a way to add system calls without recompiling the kernel using modules as a wrapper, but that is beyond the scope of this document". source http://hekimian-williams.com/?p=20

I know implementing system call statically will require me to compile the kernel code each time i make any changes. Is there a way as specified in the above mentioned blog that i can implement it as a module.

Any suggestions or pointers in the direction are much appreciated.

回答1:

1. Locate sys_call_table/ia32_sys_call_table
2. Make a copy and modify it as you wish (let it be my_sys_call_table)
3. Locate system_call entry (this one and others)
4. Modify NR_syscalls compare instruction in case of table size has changed

5. Modify sys_call_table reference at system_call to point to my_sys_call_table:

   500        call *sys_call_table(,%eax,4)
         ->
   500        call *my_sys_call_table(,%eax,4)
   

6. Profit?

Have fun :)

来源：https://stackoverflow.com/questions/12623066/implementing-linux-system-call-using-lkm