【经验分享】Frida获取RegisterNatives动态注册的JNI函数的地址
背景：某JNI的native函数在so的导出表中找不到，说明不是静态注册的，是通过RegisterNatives动态注册的（示例：https://blog.csdn.net/qq_29848853/article/details/129375219）。

可以使用Frida HOOK libart.so中的RegisterNatives函数，来曝出JNI函数的详细信息。

function hook_RegisterNatives() {
var symbols = Module.enumerateSymbolsSync("libart.so");
var addrRegisterNatives = null;
for (var i = 0; i < symbols.length; i++) {
var symbol = symbols[i];

//_ZN3art3JNI15RegisterNativesEP7_JNIEnvP7_jclassPK15JNINativeMethodi
if (symbol.name.indexOf("art") >= 0 &&
symbol.name.indexOf("JNI") >= 0 &&
symbol.name.indexOf("RegisterNatives") >= 0 &&
symbol.name.indexOf("CheckJNI") < 0) {
addrRegisterNatives = symbol.address;
console.log("RegisterNatives is at ", symbol.address, symbol.name);
}
}

if (addrRegisterNatives != null) {
Interceptor.attach(addrRegisterNatives, {
onEnter: function (args) {
console.log("[RegisterNatives] method_count:", args[3]);
var env = args[0];
var java_class = args[1];
var class_name = Java.vm.tryGetEnv().getClassName(java_class);
//console.log(class_name);

var methods_ptr = ptr(args[2]);

var method_count = parseInt(args[3]);
for (var i = 0; i < method_count; i++) {
var name_ptr = Memory.readPointer(methods_ptr.add(i * Process.pointerSize * 3));
var sig_ptr = Memory.readPointer(methods_ptr.add(i * Process.pointerSize * 3 + Process.pointerSize));
var fnPtr_ptr = Memory.readPointer(methods_ptr.add(i * Process.pointerSize * 3 + Process.pointerSize * 2));

var name = Memory.readCString(name_ptr);
var sig = Memory.readCString(sig_ptr);
var find_module = Process.findModuleByAddress(fnPtr_ptr);
console.log("[RegisterNatives] java_class:", class_name, "name:", name, "sig:", sig, "fnPtr:", fnPtr_ptr, "module_name:", find_module.name, "module_base:", find_module.base, "offset:", ptr(fnPtr_ptr).sub(find_module.base));

}
}
});
}
}

setImmediate(hook_RegisterNatives);

代码来源：https://github.com/lasting-yang/frida_hook_libart

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