On Wed, Nov 23, 2011 at 3:57 PM, Alexandru Juncu <alex.juncu@rosedu.org>wrote:
On Wed, Nov 23, 2011 at 12:10 PM, Daniel Baluta <daniel.baluta@gmail.com> wrote:
On Wed, Nov 23, 2011 at 11:22 AM, Alexandru Juncu <alex.juncu@rosedu.org> wrote:
On Wed, Nov 23, 2011 at 10:40 AM, Geraint Yang <geraint0923@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...
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You can get the address of the sys_call_table from the /proc/kallsyms and regarding the read-only section of the this symbol you can re-map the addresses by making use of vmap api in kernel. This will avoid the need for the compilation of the kernel. But I would not recommend you to do this. Their is LSM framework specifically available for this try to see if you can make use of that. Regards, Rohan Puri