there are errors to replace Linux kernel function - c

Question

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/types.h>
#define CODESIZE 7
static unsigned char original_code[CODESIZE];
static unsigned char jump_code[CODESIZE] =
"\xb8\x00\x00\x00\x00" /* movq $0, %rax */
"\xff\xe0" /* jump *%rax */
;
void (*sync_readahead)( struct address_space *mapping, struct file_ra_state *ra, struct file *filp, pgoff_t offset, unsigned long req_size ) = (void (*)(struct address_space *, struct file_ra_state *, struct file *, pgoff_t , unsigned long ) )0xc0197100;
int hijack_start(void);
void hijack_stop(void);
void intercept_init(void);
void intercept_start(void);
void intercept_stop(void);
void fake_printk(struct address_space *mapping, struct file_ra_state *ra, struct file *filp, pgoff_t offset, unsigned long req_size);
int hijack_start()
{
printk(KERN_INFO "I can haz hijack?\n" );
intercept_init();
return 0;
}
void hijack_stop()
{
intercept_stop();
return;
}
void intercept_init()
{
printk(KERN_INFO "in the intercept_init\n" );
memcpy( original_code, sync_readahead, 7 );
*(long *)&jump_code[1] = (long)fake_printk;
memcpy( sync_readahead, jump_code, 7 );
printk(KERN_INFO "in the hijack?\n" );
//real_printk=NULL;
printk(KERN_INFO "begin the hijack?\n" );
memcpy( sync_readahead, jump_code, CODESIZE );
printk(KERN_INFO "begin the hijack?\n" );
return;
}
void intercept_stop()
{
memcpy( sync_readahead, original_code, CODESIZE );
}
void fake_printk(struct address_space *map, struct file_ra_state *a, struct file *fil, pgoff_t offse, unsigned long req_siz)
{
printk(KERN_INFO "in the fake printk\n");
// return ret;
}
MODULE_LICENSE("GPL");
module_init( hijack_start );
module_exit( hijack_stop );
I want to replace Linux kernel function by address (/proc/kallsyms), but when I memcpy the new function to the address (Linux kernel):
memcpy( sync_readahead, jump_code, CODESIZE );
there are errors (segmentation fault). I have seen some examples to replace Linux kernel function in the same way. Would you please help me to solve the problem? Thank you very much.
Information as follows:
ubuntu kernel: [ 574.826458] *pde = 0087d067 *pte = 00197161
ubuntu kernel: [ 574.826468] Modules linked in: hijack(+) test(+) binfmt_misc bridge stp bnep input_polldev video output vmblock vsock vmmemctl vmhgfs pvscsi acpiphp lp ppdev pcspkr psmouse serio_raw snd_ens1371 gameport snd_ac97_codec ac97_bus snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_dummy snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer snd_seq_device snd soundcore snd_page_alloc vmci i2c_piix4 parport_pc parport intel_agp agpgart shpchp mptspi mptscsih mptbase scsi_transport_spi floppy fbcon tileblit font bitblit softcursor vmxnet
ubuntu kernel: [ 574.826491]
ubuntu kernel: [ 574.826493] Pid: 4694, comm: insmod Tainted: G D (2.6.28-11-generic #42-Ubuntu) VMware Virtual Platform
ubuntu kernel: [ 574.826496] EIP: 0060:[<f7c92101>] EFLAGS: 00010246 CPU: 0
ubuntu kernel: [ 574.826498] EIP is at intercept_init+0x41/0x70 [hijack]
ubuntu kernel: [ 574.826499] EAX: f5ec4b60 EBX: 00000000 ECX: ffffffff EDX: 00004c4c
ubuntu kernel: [ 574.826501] ESI: f7c9252c EDI: c0197100 EBP: f5edbe18 ESP: f5edbe0c
ubuntu kernel: [ 574.826502] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
ubuntu kernel: [ 574.826506] f7c921a6 f7c92130 00000000 f5edbe24 f7c92147 f7c921d5 f5edbf8c c010111e
ubuntu kernel: [ 574.826618] ---[ end trace ccc07e4b4d814976 ]---

Answer 1

Kernel function hijacking is very tricky business, and it needs to be exactly right in order to not run into all kinds of issues.
I am currently working on a module that does this, and it (at the time of this writing) works for 2.6.18+ kernels:
https://github.com/cormander/tpe-lkm
You'll be most interested in the hijacks.c file.
Many portions of this process are architecture, kernel version dependent, and CPU feature dependent as well.
UPDATE
The module now uses the 0XE9 jump opcode and should work for you. The nitty gritty details are in hijacks.c, and the "high level" logic you'll be most interested in is in the hijack_syscalls() function in security.c