ElfHook 0

modify PLT to hook api, supported android 5\6.

3 years after

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 DT_REL and DT_RELSZ in .dynmaic section, but DT_ANDROID_REL and DT_ANDROID_RELSZ instead.

  • 计算动态库加载的base_addr是错误的,应该使用bias_addr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PROT_EXEC和PROT_WRITE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 NDK_PROJECT_PATH=. NDK_OUT=./objs NDK_LIBS_OUT=./bin APP_BUILD_SCRIPT=./Android.mk APP_PLATFORM=android-23 APP_ABI=arm64-v8a,armeabi-v7a APP_STL=stlport_static

0x03 How To Use

elf_module is a shared library or executable, elf_hooker is wrapper of hook function.

  • bool elf_hooker::phrase_proc_maps()

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

  • void elf_hooker::dump_module_list()

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

  • void elf_hooker::set_prehook_cb( prehook_cb ):

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

bool prehook_cb(const char module_name, const char func_name);

 module_name: the full filename of shared library or executable.

 func_name: function name would be hooked.

  • void elf_hooker::hook_all_modules(const char *func_name, void *pfn_new, void** ppfn_old)

hook a function of all the modules, MUST call phrase_proc_maps() before hook_all_modules()

 func_name: the name of function that will be hooked.

 pfn_new: new function pointer

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

  • bool elf_hooker::hook(elf_module *module, const char* func_name, void *pfn_new, void **ppfn_old)

hook a function of a single module.

 module: pointer of elf_module.

 other parameters is the same as hook_all_modules()


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