目前 Android 上 Hook 的框架已经很多了，但是支持 Java Native 方法的 Hook 却很少，这些框架将 native 方法当普通方法 Hook，适配不同架构复杂等等。本文介绍一种 Android 版本通用的 Java Native Hook 方法并实现代码很少，下面进入我们的分析。
目前 native 方法只有两种方式
根据上面两种方式很自然想到了两种 Hook 方法
RegisterNatives 最新源码实现位置在 art/runtime/jni/jni_internal.cc，其源码如下：
这个方法主要进行各种验证并查找方法对应的 ArtMethod，其中 FastNative 在 Android8.0 以后已经采用注解的方式了，最终调用 class_linker->RegisterNative(soa.Self(), m, fnPtr) 来完成函数注册，接着分析
有关 JVMTI 大家可以网上搜索，通过它能做到很多黑科技并且这里也使用了它修改后的 new_native_method，因此通过 JVMTI 也能达到 Hook。 ，这里判断 CriticalNative 如果没有初始化类则先要初始化类，然后再注册。最终实现注册的是 method->SetEntryPointFromJni(new_native_method)
最终只是设置 ArtMethod 对象中的 jni 入口点指针为我们的注册函数，上面是主分支代码分析，Android 11 及以下都是调用的 ArtMethod::RegisterNative方法
这里可以看到在 Android 9 以上直接调用即可覆盖掉，Android 9 以下需要清理 FastNative 标志
经过上面分析要 Hook 则只需要调用 RegisterNatives 方法，而我们还要备份原方法方便后面可以调用，而原方法的地址在 ArtMethod 对象中的 jni 入口指针中保存，因此需要查找 ArtMethod，为了简单适配不同我们自己手动注册一个函数，然后再拿这个地址跟 ArtMethod 对象中去比较获取偏移量
在 Android 9 以下如果原方法是 FastNative 类型则还需要清除标志，因此还要查找 uint32_t accessFlags 成员的偏移，这里我们又采用查找的方式，来确定偏移，使用 uint32_t 对齐，我这里选择的是 0x109 标志也就是 public static native，这里最好要有 public 标志 0x1，因为正常指针都是 4/8 字节对齐的，这样避免误判
fake-linker 集成 JNI，Java native 函数 Hook，LD_PRELOAD 模式的 PLT Hook，Android 7以上绕过命名空间限制等等
数据滤镜 用于分析恶意软件，提供高度自由的数据过滤，文件重定向，maps 文件过滤，动态符号查找过滤等等
点击 这里
extern "C"
JNIEXPORT void JNICALL Java_com_sanfengandroid_fakelinker_FakeLinker_setLogLevel(JNIEnv *env, jclass clazz, jint level) {
g_log_level = level;
}
extern "C"
JNIEXPORT void JNICALL Java_com_sanfengandroid_fakelinker_FakeLinker_setLogLevel(JNIEnv *env, jclass clazz, jint level) {
g_log_level = level;
}
static jint RegisterNatives(JNIEnv* env,
jclass java_class,
const JNINativeMethod* methods,
jint method_count) {
if (UNLIKELY(method_count < 0)) {
JavaVmExtFromEnv(env)->JniAbortF("RegisterNatives", "negative method count: %d",
method_count);
return JNI_ERR; // Not reached except in unit tests.
}
CHECK_NON_NULL_ARGUMENT_FN_NAME("RegisterNatives", java_class, JNI_ERR);
ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
ScopedObjectAccess soa(env);
StackHandleScope<1> hs(soa.Self());
Handle<mirror::Class> c = hs.NewHandle(soa.Decode<mirror::Class>(java_class));
if (UNLIKELY(method_count == 0)) {
LOG(WARNING) << "JNI RegisterNativeMethods: attempt to register 0 native methods for "
<< c->PrettyDescriptor();
return JNI_OK;
}
CHECK_NON_NULL_ARGUMENT_FN_NAME("RegisterNatives", methods, JNI_ERR);
for (jint i = 0; i < method_count; ++i) {
const char* name = methods[i].name;
const char* sig = methods[i].signature;
const void* fnPtr = methods[i].fnPtr;
if (UNLIKELY(name == nullptr)) {
ReportInvalidJNINativeMethod(soa, c.Get(), "method name", i);
return JNI_ERR;
} else if (UNLIKELY(sig == nullptr)) {
ReportInvalidJNINativeMethod(soa, c.Get(), "method signature", i);
return JNI_ERR;
} else if (UNLIKELY(fnPtr == nullptr)) {
ReportInvalidJNINativeMethod(soa, c.Get(), "native function", i);
return JNI_ERR;
}
bool is_fast = false;
if (*sig == '!') {
is_fast = true;
++sig;
}
// 上面是一些参数验证
ArtMethod* m = nullptr;
bool warn_on_going_to_parent = down_cast<JNIEnvExt*>(env)->GetVm()->IsCheckJniEnabled();
for (ObjPtr<mirror::Class> current_class = c.Get();
current_class != nullptr;
current_class = current_class->GetSuperClass()) {
// 查询方法对应的 ArtMethod 对象
m = FindMethod<true>(current_class, name, sig);
if (m != nullptr) {
break;
}
// Search again comparing to all methods, to find non-native methods that match.
m = FindMethod<false>(current_class, name, sig);
if (m != nullptr) {
break;
}
if (warn_on_going_to_parent) {
LOG(WARNING) << "CheckJNI: method to register \"" << name << "\" not in the given class. "
<< "This is slow, consider changing your RegisterNatives calls.";
warn_on_going_to_parent = false;
}
}
if (m == nullptr) {
c->DumpClass(LOG_STREAM(ERROR), mirror::Class::kDumpClassFullDetail);
LOG(ERROR)
<< "Failed to register native method "
<< c->PrettyDescriptor() << "." << name << sig << " in "
<< c->GetDexCache()->GetLocation()->ToModifiedUtf8();
ThrowNoSuchMethodError(soa, c.Get(), name, sig, "static or non-static");
return JNI_ERR;
} else if (!m->IsNative()) {
// 非 native 方法是不能注册的
LOG(ERROR)
<< "Failed to register non-native method "
<< c->PrettyDescriptor() << "." << name << sig
<< " as native";
ThrowNoSuchMethodError(soa, c.Get(), name, sig, "native");
return JNI_ERR;
}
VLOG(jni) << "[Registering JNI native method " << m->PrettyMethod() << "]";
if (UNLIKELY(is_fast)) {
LOG(WARNING) << "!bang JNI is deprecated. Switch to @FastNative for " << m->PrettyMethod();
is_fast = false;
// TODO: make this a hard register error in the future.
}
// 最终调用 class_linker->RegisterNative 来实际进行注册
const void* final_function_ptr = class_linker->RegisterNative(soa.Self(), m, fnPtr);
UNUSED(final_function_ptr);
}
return JNI_OK;
}
static jint RegisterNatives(JNIEnv* env,
jclass java_class,
const JNINativeMethod* methods,
jint method_count) {
if (UNLIKELY(method_count < 0)) {
JavaVmExtFromEnv(env)->JniAbortF("RegisterNatives", "negative method count: %d",
method_count);
return JNI_ERR; // Not reached except in unit tests.
}
CHECK_NON_NULL_ARGUMENT_FN_NAME("RegisterNatives", java_class, JNI_ERR);
ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
ScopedObjectAccess soa(env);
StackHandleScope<1> hs(soa.Self());
Handle<mirror::Class> c = hs.NewHandle(soa.Decode<mirror::Class>(java_class));
if (UNLIKELY(method_count == 0)) {
LOG(WARNING) << "JNI RegisterNativeMethods: attempt to register 0 native methods for "
<< c->PrettyDescriptor();
return JNI_OK;
}
CHECK_NON_NULL_ARGUMENT_FN_NAME("RegisterNatives", methods, JNI_ERR);
for (jint i = 0; i < method_count; ++i) {
const char* name = methods[i].name;
const char* sig = methods[i].signature;
const void* fnPtr = methods[i].fnPtr;
if (UNLIKELY(name == nullptr)) {
ReportInvalidJNINativeMethod(soa, c.Get(), "method name", i);
return JNI_ERR;
} else if (UNLIKELY(sig == nullptr)) {
ReportInvalidJNINativeMethod(soa, c.Get(), "method signature", i);
return JNI_ERR;
} else if (UNLIKELY(fnPtr == nullptr)) {
ReportInvalidJNINativeMethod(soa, c.Get(), "native function", i);
return JNI_ERR;
}
bool is_fast = false;
if (*sig == '!') {
is_fast = true;
++sig;
}
// 上面是一些参数验证
ArtMethod* m = nullptr;
bool warn_on_going_to_parent = down_cast<JNIEnvExt*>(env)->GetVm()->IsCheckJniEnabled();
for (ObjPtr<mirror::Class> current_class = c.Get();
current_class != nullptr;
current_class = current_class->GetSuperClass()) {
// 查询方法对应的 ArtMethod 对象
m = FindMethod<true>(current_class, name, sig);
if (m != nullptr) {
break;
}
// Search again comparing to all methods, to find non-native methods that match.
m = FindMethod<false>(current_class, name, sig);
if (m != nullptr) {
break;
}
if (warn_on_going_to_parent) {
LOG(WARNING) << "CheckJNI: method to register \"" << name << "\" not in the given class. "
<< "This is slow, consider changing your RegisterNatives calls.";
warn_on_going_to_parent = false;
}
}
if (m == nullptr) {
c->DumpClass(LOG_STREAM(ERROR), mirror::Class::kDumpClassFullDetail);
LOG(ERROR)
<< "Failed to register native method "
<< c->PrettyDescriptor() << "." << name << sig << " in "
<< c->GetDexCache()->GetLocation()->ToModifiedUtf8();
ThrowNoSuchMethodError(soa, c.Get(), name, sig, "static or non-static");
return JNI_ERR;
} else if (!m->IsNative()) {
// 非 native 方法是不能注册的
LOG(ERROR)
<< "Failed to register non-native method "
<< c->PrettyDescriptor() << "." << name << sig
<< " as native";
ThrowNoSuchMethodError(soa, c.Get(), name, sig, "native");
return JNI_ERR;
}
VLOG(jni) << "[Registering JNI native method " << m->PrettyMethod() << "]";
if (UNLIKELY(is_fast)) {
LOG(WARNING) << "!bang JNI is deprecated. Switch to @FastNative for " << m->PrettyMethod();
is_fast = false;
// TODO: make this a hard register error in the future.
}
// 最终调用 class_linker->RegisterNative 来实际进行注册
const void* final_function_ptr = class_linker->RegisterNative(soa.Self(), m, fnPtr);
UNUSED(final_function_ptr);
}
return JNI_OK;
}
const void* ClassLinker::RegisterNative(
Thread* self, ArtMethod* method, const void* native_method) {
CHECK(method->IsNative()) << method->PrettyMethod();
CHECK(native_method != nullptr) << method->PrettyMethod();
void* new_native_method = nullptr;
Runtime* runtime = Runtime::Current();
// 这里 JVMTI 响应注册事件
runtime->GetRuntimeCallbacks()->RegisterNativeMethod(method,
native_method,
/*out*/&new_native_method);
if (method->IsCriticalNative()) {
MutexLock lock(self, critical_native_code_with_clinit_check_lock_);
// Remove old registered method if any.
auto it = critical_native_code_with_clinit_check_.find(method);
if (it != critical_native_code_with_clinit_check_.end()) {
critical_native_code_with_clinit_check_.erase(it);
}
// To ensure correct memory visibility, we need the class to be visibly
// initialized before we can set the JNI entrypoint.
if (method->GetDeclaringClass()->IsVisiblyInitialized()) {
method->SetEntryPointFromJni(new_native_method);
} else {
critical_native_code_with_clinit_check_.emplace(method, new_native_method);
}
} else {
method->SetEntryPointFromJni(new_native_method);
}
return new_native_method;
}
const void* ClassLinker::RegisterNative(
Thread* self, ArtMethod* method, const void* native_method) {
CHECK(method->IsNative()) << method->PrettyMethod();
CHECK(native_method != nullptr) << method->PrettyMethod();
void* new_native_method = nullptr;
Runtime* runtime = Runtime::Current();
// 这里 JVMTI 响应注册事件
runtime->GetRuntimeCallbacks()->RegisterNativeMethod(method,
native_method,
/*out*/&new_native_method);
if (method->IsCriticalNative()) {
MutexLock lock(self, critical_native_code_with_clinit_check_lock_);
// Remove old registered method if any.
auto it = critical_native_code_with_clinit_check_.find(method);
if (it != critical_native_code_with_clinit_check_.end()) {
critical_native_code_with_clinit_check_.erase(it);
}
// To ensure correct memory visibility, we need the class to be visibly
// initialized before we can set the JNI entrypoint.
if (method->GetDeclaringClass()->IsVisiblyInitialized()) {
method->SetEntryPointFromJni(new_native_method);
} else {
critical_native_code_with_clinit_check_.emplace(method, new_native_method);
}
} else {
method->SetEntryPointFromJni(new_native_method);
}
return new_native_method;
}
void SetEntryPointFromJni(const void* entrypoint)
REQUIRES_SHARED(Locks::mutator_lock_) {
// The resolution method also has a JNI entrypoint for direct calls from
// compiled code to the JNI dlsym lookup stub for @CriticalNative.
DCHECK(IsNative() || IsRuntimeMethod());
SetEntryPointFromJniPtrSize(entrypoint, kRuntimePointerSize);
}
void SetEntryPointFromJni(const void* entrypoint)
REQUIRES_SHARED(Locks::mutator_lock_) {
// The resolution method also has a JNI entrypoint for direct calls from
// compiled code to the JNI dlsym lookup stub for @CriticalNative.
DCHECK(IsNative() || IsRuntimeMethod());
SetEntryPointFromJniPtrSize(entrypoint, kRuntimePointerSize);
}
// Android 9 ~ 11
const void* ArtMethod::RegisterNative(const void* native_method) {
CHECK(IsNative()) << PrettyMethod();
CHECK(native_method != nullptr) << PrettyMethod();
void* new_native_method = nullptr;
Runtime::Current()->GetRuntimeCallbacks()->RegisterNativeMethod(this,
native_method,
/*out*/&new_native_method);
SetEntryPointFromJni(new_native_method);
return new_native_method;
}
// Android 9 以下
const void* ArtMethod::RegisterNative(const void* native_method, bool is_fast) {
CHECK(IsNative()) << PrettyMethod();
// 多了一个 FastNative 检测,在已经注册为 FastNative 后不能再次注册
CHECK(!IsFastNative()) << PrettyMethod();
CHECK(native_method != nullptr) << PrettyMethod();
if (is_fast) {
AddAccessFlags(kAccFastNative);
}
void* new_native_method = nullptr;
Runtime::Current()->GetRuntimeCallbacks()->RegisterNativeMethod(this,
native_method,
/*out*/&new_native_method);
SetEntryPointFromJni(new_native_method);
return new_native_method;
}
// Android 9 ~ 11
const void* ArtMethod::RegisterNative(const void* native_method) {
CHECK(IsNative()) << PrettyMethod();
CHECK(native_method != nullptr) << PrettyMethod();
void* new_native_method = nullptr;
Runtime::Current()->GetRuntimeCallbacks()->RegisterNativeMethod(this,
native_method,
/*out*/&new_native_method);
SetEntryPointFromJni(new_native_method);
return new_native_method;
}
// Android 9 以下
const void* ArtMethod::RegisterNative(const void* native_method, bool is_fast) {
CHECK(IsNative()) << PrettyMethod();
// 多了一个 FastNative 检测,在已经注册为 FastNative 后不能再次注册
CHECK(!IsFastNative()) << PrettyMethod();
CHECK(native_method != nullptr) << PrettyMethod();
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