代码实例分析android中inline hook

target.h
#ifndef TARGET_H_INCLUDED
#define TARGET_H_INCLUDED
void target_foo();
#endif // TARGET_H_INCLUDED
target.c
#include "target.h"
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
void target_foo()
{
 int a = 3;
 int b = 2;
 while(a--) {
  sleep(2);
  b = a * b;
  printf("[INFO] b is %d\n", b);
 }
 b = b + 2;
 b = b - 1;
 printf("[INFO] finally, b is %d\n", b);
}

Android.mk
include $(CLEAR_VARS)
LOCAL_ARM_MODE := arm
LOCAL_MODULE := target
LOCAL_CFLAGS += -pie -fPIE -std=c11
LOCAL_LDFLAGS += -pie -fPIE -shared -llog
APP_ABI := armeabi-v7a
LOCAL_SRC_FILES := target.c
include $(BUILD_SHARED_LIBRARY)

main.c
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <unistd.h>
#include <stdbool.h>
#include "hook_inline.h"
typedef void (*target_foo)(void);
void my_func(struct hook_reg *reg)
{
 puts("here we go!");
}
void main()
{
 void *handler = dlopen("/data/local/tmp/libtarget.so", RTLD_NOW);
 target_foo foo = (target_foo)dlsym(handler, "target_foo");
 hook_inline_make("/data/local/tmp/libtarget.so", 0xde2, my_func, true);
 foo();
}
hook_inline.h
#ifndef HOOK_INLINE_H_INCLUDED
#define HOOK_INLINE_H_INCLUDED
#include <stdbool.h>
struct hook_reg {
 long ARM_r0; long ARM_r1; long ARM_r2; long ARM_r3;
 long ARM_r4; long ARM_r5; long ARM_r6; long ARM_r7;
 long ARM_r8; long ARM_r9; long ARM_r10;long ARM_r11;
 long ARM_r12;long ARM_sp; long ARM_lr; long ARM_cpsr;
};
typedef void (*hook_func)(struct hook_reg *reg);
bool hook_inline_make(const char *library, long address, hook_func func, bool isArm);
#endif // HOOK_INLINE_H_INCLUDED

long get_module_addr(pid_t pid, const char *module_name)
{
 char file_path[256];
 char file_line[512];
 if (pid < 0) {
  snprintf(file_path, sizeof(file_path), "/proc/self/maps");
 } else {
  snprintf(file_path, sizeof(file_path), "/proc/%d/maps", pid);
 }
 FILE *fp = fopen(file_path, "r");
 if (fp == NULL) {
  return -1;
 }
 long addr_start = -1, addr_end = 0;
 while (fgets(file_line, sizeof(file_line), fp)) {
  if (strstr(file_line, module_name)) {
   if (2 == sscanf(file_line, "%8lx-%8lx", &addr_start, &addr_end)) {
    break;
   }
  }
 }
 fclose(fp);
 printf("library :%s %lx-%lx, pid : %d\n", module_name, addr_start, addr_end, pid);
 return addr_start;
}

bool change_addr_writable(long address, bool writable) {
 long page_size = sysconf(_SC_PAGESIZE);
 //align address by page size
 long page_start = (address) & (~(page_size - 1));
 //change memory attribute
 if (writable == true) {
  return mprotect((void*)page_start, page_size, PROT_READ | PROT_WRITE | PROT_EXEC) != -1;
 } else {
  return mprotect((void*)page_start, page_size, PROT_READ | PROT_EXEC) != -1;
 }
}

ellcode.S 1 .global _shellcode_start_s
 .global _shellcode_end_s
 .global _hook_func_addr_s
 .global _stub_func_addr_s
 .data
 _shellcode_start_s:
     @ 备份各个寄存器
     push  {r0, r1, r2, r3}
     mrs   r0, cpsr
     str   r0, [sp, #0xc]
     str   r14, [sp, #0x8]
     add   r14, sp, #0x10
     str   r14, [sp, #0x4]
     pop   {r0}
     push  {r0-r12}
     @ 此时寄存器被备份在栈中，将栈顶地址作为回调函数的参数（struct hook_reg）
     mov   r0, sp
     ldr   r3, _hook_func_addr_s
     blx   r3
     @ 恢复寄存器值
     ldr   r0, [sp, #0x3c]
     msr   cpsr, r0
     ldmfd sp!, {r0-r12}
     ldr   r14, [sp, #0x4]
     ldr   sp, [r13]
     ldr   pc, _stub_func_addr_s
 _hook_func_addr_s:
 .word 0x0
 _stub_func_addr_s:
 .word 0x0
 _shellcode_end_s:
 .end

 void hook_inline_make(const char *library, long address, hook_func func)
 {
     //获取hook点在内存中的地址
     long base_addr = get_module_addr(-1, library);
     long hook_addr = base_addr + address;
     //获取shellcode中的符号地址
  extern long _shellcode_start_s;
     extern long _shellcode_end_s;
     extern long _hook_func_addr_s;
     extern long _stub_func_addr_s;
     void *p_shellcode_start = &_shellcode_start_s;
     void *p_shellcdoe_end = &_shellcode_end_s;
     void *p_hook_func = &_hook_func_addr_s;
     void *p_stub_func = &_stub_func_addr_s;
     //计算shellcode大小
     int shellcode_size = (int)(p_shellcdoe_end - p_shellcode_start);
     //新建shellcode
     void *shellcode = malloc(shellcode_size);
     memcpy(shellcode, p_shellcode_start, shellcode_size);
     //添加执行属性
     change_addr_writable((long)shellcode, true);
     //在32bit的arm指令集中，stubcode中的4条指令占用16个字节的空间
     //前两条指令为hook点被替换的两条指令
     //后两条指令跳转回原程序
     void *stubcode = malloc(16);
     memcpy(stubcode, (void*)hook_addr, 8);
     //ldr pc, [pc, #-4]
     //[address]
     //手动填充stubcode
     char jump_ins[8] = {0x04, 0xF0, 0x1F, 0xE5};
     uint32_t jmp_address = hook_addr + 8;
     memcpy(jump_ins + 4, &jmp_address, 4);
     memcpy(stubcode + 8, jump_ins, 8);
     //添加执行属性
     change_addr_writable((long)stubcode, true);
     //修复shellcode中的两个地址值
     uint32_t *shell_hook = shellcode + (p_hook_func - p_shellcode_start);
     *shell_hook = (uint32_t)func;
     uint32_t *shell_stub = shellcode + (p_stub_func - p_shellcode_start);
     *shell_stub = (uint32_t)stubcode;
     //为hook点添加写属性
     change_addr_writable(hook_addr, true);
     //替换hook点指令为跳转指令，跳转至shellcode
     jmp_address = (uint32_t)shellcode;
     memcpy(jump_ins + 4, &jmp_address, 4);
     memcpy((void*)hook_addr, jump_ins, 8);
     change_addr_writable(hook_addr, false);
     //刷新cache
     cacheflush(hook_addr, 8, 0);
 }