[prev in list] [next in list] [prev in thread] [next in thread] 

List:       kernelnewbies
Subject:    Re: sys_call_table
From:       "Vamsi Krishna S ." <vamsi () in ! ibm ! com>
Date:       2003-01-31 12:44:23
[Download RAW message or body]

sys_call_table is not exported anymore for kernel modules to
tinker with (for a number of good reasons mentioned elsewhere).

This code is groping in the kernel address space to figure
out the location of the sys_call_table.

On Fri, Jan 31, 2003 at 05:24:06PM +0530, Mohanasundaram C wrote:
> Hi All,
> 
> 	I tried to understand the code below but could not. Can any one please explain me.
> 
> Regards,
> Mohan.
> 
> #include <linux/syscall.h>
> #include <asm/unistd.h>
> 
> static void **sys_call_table;
> 
> //nearest exported symbol to syscalls in my kernel,
> //i hope in others kernels too
> //but in other form you can look at your kernel sources
> 
> extern void *system_utsname;
> 
> ....
> 
> static int locate_sys_call_table(void) {
>     unsigned long *begin;
>     int i;
> 
>     begin=(unsigned long *) &system_utsname;
>     for (i=0;i<1024;i++) {
>         if (*(begin+i)==(unsigned long) sys_socketcall) {
>             sys_call_table=(void *) (begin+i-__NR_socketcall);
>             //are you sure?
>             if (sys_call_table[__NR_exit]==(void *) sys_exit) {
>                 printk("success: located sys_call_table: %X\n",(unsigned
> int) sys_call_table);
>                 return(1);
>             }
>         }
>     }
>     return(0);
> }
> 
> 
> int __init init_exportmodule (void)
> {
> 
>     if (!locate_sys_call_table()) {
>         // ... cry again and return error
>     }
> 
>     //.....sys_call_table[] works now!!
>     //......do something like export symbol
>     //.... or intercept any syscall
> 
> }
> --
> Kernelnewbies: Help each other learn about the Linux kernel.
> Archive:       http://mail.nl.linux.org/kernelnewbies/
> FAQ:           http://kernelnewbies.org/faq/
> 

-- 
Vamsi Krishna S.
Linux Technology Center,
IBM Software Lab, Bangalore.
Ph: +91 80 5044959
Internet: vamsi@in.ibm.com
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/

[prev in list] [next in list] [prev in thread] [next in thread]