How to hook the system call?

[Alexandru Juncu]

On Wed, Nov 23, 2011 at 12:10 PM, Daniel Baluta <daniel.baluta at gmail.com> wrote:
> On Wed, Nov 23, 2011 at 11:22 AM, Alexandru Juncu <alex.juncu at rosedu.org> wrote:
>> On Wed, Nov 23, 2011 at 10:40 AM, Geraint Yang <geraint0923 at gmail.com> wrote:
>>> Hello everyone,
>>>
>>> I am going to hook a system call like 'read' or 'send' by modifying the
>>> sys_call_table, but it seems that the sys_call_table is in read only page,
>>> how can I set modify the sys_call_table ? Or if there any method that I can
>>> use to hook a system call in module without modify the kernel source?
>>>
>>> Thanks!
>>
>> On a 2.6.35 kernel, it worked for me just by changing an entry in the
>> sys_call_table, within a kernel module.  Something like this:
>
> Alex,
> I am pretty sure that you are using a hacked version of 2.6.35.
>
> Geraint,
> In order to be able to hook a syscall you must do the following:
>
> 1. export syscall_table in arch/x86/kernel/i386_ksyms_32.c
>
> extern void* sys_call_table[];
> EXPORT_SYMBOL(sys_call_table);
>
> 2. make sys_call_table writebale. In arch/x86/kernel/entry_32.S
> you must have:
>
> .section .data,"a"
> #include "syscall_table_32.S"
>
> thanks,
> Daniel.
>

Ah, Daniel is right... I forgot about that part...