0x01 Brief About ElfHook

  这份ElfHook的代码参考boyliang的AllHookInOne, 修复AllHookInOne的 ElfHook中的一些问题，同时也解决我们项目中遇到的一些问题。

• NOT DT_HAST in .dynmaic section，but .gun.hash instead.

• NOT DTREL and DTRELSZ in .dynmaic section, but DTANDROIDREL and DTANDROIDRELSZ instead.

• 计算动态库加载的baseaddr是错误的，应该使用biasaddr来计算出ehdr、phdr和shdr之外的所有地址。

• 替换函数时，修改page的读写权限时，在SEAndroid上PROTEXEC和PROTWRITE同时设置可能会导致异常，

• after hook "dlopen" function, how to get base_addr from return value of old dlopen in new dlopen function.

• support aarch64 (arm64-v8a)

ref:

 AllHookInOne : [https://github.com/boyliang/AllHookInOne.git]

 AllHookInOne说明 : [http://bbs.pediy.com/showthread.php?p=1328038]

 bionic : [https://android.googlesource.com/platform/bionic]

0x02 How To Build

Export android ndk path

export -p PATH=$PATH:$ANDROID_NDK

Build

make

make clean

make install # copy libElfHook.so to jniLibs dir in Demo.

or

ndk-build NDKPROJECTPATH=. NDKOUT=./objs NDKLIBSOUT=./bin APPBUILDSCRIPT=./Android.mk APPPLATFORM=android-23 APPABI=arm64-v8a,armeabi-v7a APPSTL=stlport_static

0x03 How To Use

elfmodule is a shared library or executable, elfhooker is wrapper of hook function.

• bool elfhooker::phraseproc_maps()

phrase /proc/self/maps to create all elf modules have been loadded

• void elfhooker::dumpmodule_list()

print all elf moudle's info, base addr and full path.

• void elfhooker::setprehookcb( prehookcb ):

set a callback function, which would be invoked before hooked. if it return false, prehook_cb function like this:

bool prehookcb(const char* modulename, const char* func_name);

 module_name: the full filename of shared library or executable.

 func_name: function name would be hooked.

• void elfhooker::hookallmodules(const char *funcname, void *pfnnew, void** ppfnold)

hook a function of all the modules, MUST call phraseprocmaps() before hookallmodules()

 func_name: the name of function that will be hooked.

 pfn_new: new function pointer

 ppfnold: return raw function pointer, ppfnold MUST NOT be NULL

• bool elfhooker::hook(elfmodule *module, const char* funcname, void *pfnnew, void **ppfn_old)

hook a function of a single module.

 module: pointer of elf_module.

 other parameters is the same as hookallmodules()