一种inlineHook检测方案

定义

inlinehook是修改内存中的机器码来实现hook的方式

我们用frida查看一个函数hook之前和hook之后的机器码，这里以open函数为例：

let bytes_count = 32let address = Module.getExportByName("libc.so","open")
let before = ptr(address)console.log("")console.log("[*] before hook: ")console.log(hexdump(before, {   offset: 0,   length: bytes_count,   header: true,   ansi: true}));
let isOutput = false
Interceptor.attach(address, {onEnter:function(args){       if(isOutput) return;let after = ptr(address)       console.log("")console.log("[*] after hook: ")       console.log(hexdump(after, {           offset: 0,           length: bytes_count,           header: true,           ansi: true      }))       isOutput = true},onLeave:function(retv){}});

hook之前：

hook之后：

可见，hook之后，函数开头的字节被修改了

思考

inlinehook只修改了内存中的机器码，而内存中的机器码是从文件加载而来的，所以我们可以将函数在内存中字节和本地对应的字节进行比较，如果不一致，那么可以认为内存中的字节被修改了，即被inlinehook了。

实现

#ifdef __LP64__   const char *lib_path = "/system/lib64/libc.so";#else   const char *lib_path = "/system/lib/libc.so";#endif#define CMP_COUNT 8   const char *sym_name = "open";
   struct local_dlfcn_handle *handle = static_cast<local_dlfcn_handle *>(local_dlopen(lib_path));
   off_t offset = local_dlsym(handle,sym_name);
   FILE *fp = fopen(lib_path,"rb");   char file_bytes[CMP_COUNT] = {0};   if(fp != NULL){       fseek(fp,offset,SEEK_SET);       fread(file_bytes,1,CMP_COUNT,fp);       fclose(fp);  }
   void *dl_handle = dlopen(lib_path,RTLD_NOW);   void *sym = dlsym(dl_handle,sym_name);
   int is_hook = memcmp(file_bytes,sym,CMP_COUNT) != 0;
   local_dlclose(handle);   dlclose(dl_handle);
   char text[128] = {0};   snprintf(text,128,"Function "%s" is Hook: %s",sym_name,is_hook ? "true" : "false");

这里local_开头的函数是读取本地符号偏移库，库代码：https://github.com/luoyesiqiu/local_dlfcn

用frida hook测试demo:frida-trace -U -i "open" -f com.luoye.localdlfcn