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Simplify JNI hooking code

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topjohnwu 2025-05-17 02:05:21 -07:00
parent 34b30d7ce1
commit 0c4b8afbc5
1 changed files with 19 additions and 15 deletions
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34
native/src/core/zygisk/hook.cpp
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@ -415,10 +415,7 @@ void HookContext::hook_plt() {
ZLOGE("plt_hook failed\n");
// Remove unhooked methods
plt_backup.erase(
std::remove_if(plt_backup.begin(), plt_backup.end(),
[](auto &t) { return *std::get<3>(t) == nullptr;}),
plt_backup.end());
std::erase_if(plt_backup, [](auto &t) { return *std::get<3>(t) == nullptr; });
}
void HookContext::hook_unloader() {
@ -467,35 +464,42 @@ void HookContext::hook_jni_methods(JNIEnv *env, const char *clz, JNIMethods meth
auto total = runtime_callbacks->getNativeMethodCount(env, clazz);
auto old_methods = std::make_unique_for_overwrite<JNINativeMethod[]>(total);
runtime_callbacks->getNativeMethods(env, clazz, old_methods.get(), total);
auto new_methods = std::make_unique_for_overwrite<JNINativeMethod[]>(total);
// Replace the method
// WARNING: the signature field returned from getNativeMethods is in a non-standard format.
// DO NOT TRY TO USE IT. This is the reason why we try to call RegisterNatives on every single
// provided JNI methods directly to be 100% sure about whether a signature matches or not.
// Replace methods
for (auto &method : methods) {
// It's useful to allow nullptr function pointer for restoring hook
if (!method.fnPtr) continue;
// It's normal that the method is not found
if (env->RegisterNatives(clazz, &method, 1) == JNI_ERR ||
env->ExceptionCheck() == JNI_TRUE) {
if (env->RegisterNatives(clazz, &method, 1) == JNI_ERR || env->ExceptionCheck() == JNI_TRUE) {
if (auto exception = env->ExceptionOccurred()) {
env->DeleteLocalRef(exception);
}
env->ExceptionClear();
method.fnPtr = nullptr;
continue;
}
// Find the old function pointer and return to caller
runtime_callbacks->getNativeMethods(env, clazz, new_methods.get(), total);
}
// Fetch the new set of native methods
auto new_methods = std::make_unique_for_overwrite<JNINativeMethod[]>(total);
runtime_callbacks->getNativeMethods(env, clazz, new_methods.get(), total);
// Find the old function pointer and return to caller
for (auto &method : methods) {
if (!method.fnPtr) continue;
for (auto i = 0; i < total; ++i) {
auto &new_method = new_methods[i];
if (new_method.fnPtr == method.fnPtr && strcmp(new_method.name, method.name) == 0) {
if (new_method.fnPtr == method.fnPtr) {
auto &old_method = old_methods[i];
ZLOGD("replace %s#%s%s %p -> %p\n", clz,
method.name, method.signature, old_method.fnPtr, method.fnPtr);
ZLOGD("replace %s#%s%s %p -> %p\n", clz, method.name, method.signature, old_method.fnPtr, method.fnPtr);
method.fnPtr = old_method.fnPtr;
break;
}
}
old_methods.swap(new_methods);
}
}