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xhook

xhook is a PLT (Procedure Linkage Table) hook library for Android native ELF (executable and shared libraries).

xhook has been keeping optimized for stability and compatibility.

Features

Support Android 4.0+ (API level 14+).
Support armeabi, armeabi-v7a and arm64-v8a.
Support to lookup symbol via ELF HASH and GNU HASH.
Support to lookup reloc via ELF reloc and ANDROID reloc.
Do NOT need root permission.
Do not depends on any third-party shared libraries.
Pure C code. Small library size.

Build

You need google NDK for building xhook. See: https://developer.android.com/ndk/downloads/index.html

The latest version of xhook is developed and debugged with the NDK version r16b.

build the libraries (libxhook.so and other libraries for test)

./build_libs.sh

install the libraries to test project's libs path

./install_libs.sh

clean the libraries

./clean_libs.sh

try the demo APP

cd ./xhookwrapper/
./gradlew assembleDebug
adb install ./app/build/outputs/apk/debug/app-debug.apk

APIs

External APIs header file: libxhook/jni/xhook.h

Register hook info

int xhook_register(const char  *pathname_regex_str,  
                   const char  *symbol,  
                   void        *new_func,  
                   void       **old_func);

In current process's memory space, in every loaded ELF which pathname matches regular expression pathname_regex_str, every PLT entries to symbol will be replaced with new_func. The original one will be saved in old_func.

The new_func must have the same function declaration as the original one.

Return zero if successful, non-zero otherwise.

The regular expression for pathname_regex_str only support POSIX BRE.

Do hook

int xhook_refresh(int async);

Do the real hook operations according to the registered hook info.

Pass 1 to async for asynchronous hook. Pass 0 to async for synchronous hook.

Return zero if successful, non-zero otherwise.

xhook will keep a global cache for saving the last ELF loading info from /proc/self/maps. This cache will also be updated in xhook_refresh. With this cache, xhook_refresh can determine which ELF is newly loaded. We only need to do hook in these newly loaded ELF.

Clear cache

void xhook_clear();

Clear all cache owned by xhook, reset all global flags to default value.

If you confirm that all PLT entries you want have been hooked, you could call this function to save some memory.

Enable/Disable debug info

void xhook_enable_debug(int flag);

Pass 1 to flag for enable debug info. Pass 0 to flag for disable debug info. (xhook disable debug info by default)

Debug info will be sent to logcat with tag xhook.

Examples

//detect memory leak
xhook_register(".*\\.so$", "malloc",  my_malloc,  NULL);
xhook_register(".*\\.so$", "calloc",  my_calloc,  NULL);
xhook_register(".*\\.so$", "realloc", my_realloc, NULL);
xhook_register(".*\\.so$", "free",    my_free,    NULL);

//parse sockets lifecycle
xhook_register(".*\\.so$", "getaddrinfo", my_getaddrinfo, NULL);
xhook_register(".*\\.so$", "socket",      my_socket,      NULL);
xhook_register(".*\\.so$", "setsockopt"   my_setsockopt,  NULL);
xhook_register(".*\\.so$", "bind",        my_bind,        NULL);
xhook_register(".*\\.so$", "listen",      my_listen,      NULL);
xhook_register(".*\\.so$", "connect",     my_connect,     NULL);
xhook_register(".*\\.so$", "shutdown",    my_shutdown,    NULL);
xhook_register(".*\\.so$", "close",       my_close,       NULL);

//filter off and save some android log to local file
xhook_register(".*\\.so$", "__android_log_write",  my_log_write,  NULL);
xhook_register(".*\\.so$", "__android_log_print",  my_log_print,  NULL);
xhook_register(".*\\.so$", "__android_log_vprint", my_log_vprint, NULL);
xhook_register(".*\\.so$", "__android_log_assert", my_log_assert, NULL);

//tracking
xhook_register("^/system/.*$", "mmap",   my_mmap,   NULL);
xhook_register("^/vendor/.*$", "munmap", my_munmap, NULL);

//defense to some injection attacks
xhook_register(".*com\\.qihoo.*\\.so$", "malloc",  my_malloc_always_return_NULL, NULL);
xhook_register(".*/liblbeclient\\.so$", "connect", my_connect_with_recorder,     NULL);

//fix some system bug
xhook_register(".*samsung.*/libEGL\\.so$", "bad_code", my_nice_code, NULL);

//hook now!
xhook_refresh(1);

License

Most source code in xhook are MIT licensed. Some other source code have BSD-style licenses.

Please refer to the LICENSE file for detailed information.

Contact

github: https://github.com/iqiyi/xhook