安卓逆向入门-Native层入门

入门

动态注册方法：

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#include <jni.h>
#include <string>
#include "aes_utils.h"
#include "tools.h"
#include "junk.h"
#define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))
JNIEXPORT jstring JNICALL method02(JNIEnv *env, jclass jcls, jstring str_) {
    if (str_ == nullptr) 
        return nullptr;
    const char *str = env->GetStringUTFChars(str_, JNI_FALSE);
    char *result = AES_128_CBC_PKCS5_Decrypt(str);
    env->ReleaseStringUTFChars(str_, str);
    jstring jResult = getJString(env, result);
    free(result);
    return jResult;
}
static JNINativeMethod method_table[] = {
//        {"method01", "(Ljava/lang/String;)Ljava/lang/String;", (void *) method01},
        {"decrypt", "(Ljava/lang/String;)Ljava/lang/String;", (void *) method02},
//        (参数1类型标示；参数2类型标示；参数3类型标示...)返回值类型标示
};
static int registerMethods(JNIEnv *env, const char *className,JNINativeMethod *gMethods, int numMethods) {
    jclass clazz = env->FindClass(className);
    if (clazz == nullptr)
        return JNI_FALSE;
    if (env->RegisterNatives(clazz, gMethods, numMethods) < 0)
        return JNI_FALSE;
    return JNI_TRUE;
}
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jstring JNICALL Java_com_roysue_easyso1_MainActivity_method01(JNIEnv *env, jclass jcls, jstring str_) {
    if (str_ == nullptr) return nullptr;
    const char *str = env->GetStringUTFChars(str_, JNI_FALSE);
    char *result = AES_128_CBC_PKCS5_Encrypt(str);
    env->ReleaseStringUTFChars(str_, str);
    jstring jResult = getJString(env, result);
    free(result);
    return jResult;
}
JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
    _JUNK_FUN_0
    JNIEnv *env = nullptr;
    if (vm->GetEnv((void **) &env, JNI_VERSION_1_6) != JNI_OK)
        return JNI_ERR;
    assert(env != nullptr);
// 注册native方法
    if (!registerMethods(env, "com/roysue/easyso1/MainActivity", method_table,NELEM(method_table)))
        return JNI_ERR;
    return JNI_VERSION_1_6;
}
#ifdef __cplusplus
}
#endif

加载完SO文件后，ELF首先运行.init和.init_array，再找JNI_Onload运行。有重写JNI_Onload的实现则自动运行，没有则系统自动生成一个。SO文件被卸载时JNI_OnUnload被运行。

使用RegisterNatives进行动态注册：

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jint RegisterNatives(jclass clazz,const JNINativeMethod* methods,jint nMethods);
typedef struct{
    const char* name;
    const char* signature;
    void* fnPtr;
}JNINativeMethod;

下面Frida脚本可Hook该SO库的加载过程，并输出method01和decrypt函数的注册：

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var ENV = null;
var JCLZ = null;
var method01addr = null;
var method02addr = null;
var method02 = null;
var addrNewStringUTF = null;
var NewStringUTF = null;
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("NewStringUTF") >= 0 && symbol.name.indexOf("CheckJNI") < 0) {
            addrNewStringUTF = symbol.address;
            console.log("NewStringUTF is at ", symbol.address, symbol.name);
            NewStringUTF = new NativeFunction(addrNewStringUTF,'pointer',['pointer','pointer'])
        }
        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];
                ENV = args[0];
                var java_class = args[1];
                JCLZ = 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));
                    if(name.indexOf("method01")>=0){
                        // method01addr = fnPtr_ptr;
                        continue;
                    }else if (name.indexOf("decrypt")>=0){
                        method02addr = fnPtr_ptr;
                        method02 = new NativeFunction(method02addr,'pointer',['pointer','pointer','pointer']);
                        method01addr = Module.findExportByName("libroysue.so", "Java_com_roysue_easyso1_MainActivity_method01")
                    }else{
                        continue;
                    }
                }
            }
        });
    }
}
function invokemethod01(contents){
    console.log("method01_addr is =>",method01addr)
    var method01 = new NativeFunction(method01addr,'pointer',['pointer','pointer','pointer']);
    var NewStringUTF = new NativeFunction(addrNewStringUTF,'pointer',['pointer','pointer'])
    var result = null;
    Java.perform(function(){    
        console.log("Java.vm.getEnv()",Java.vm.getEnv())
        var JSTRING = NewStringUTF(Java.vm.getEnv(),Memory.allocUtf8String(contents))
        result = method01(Java.vm.getEnv(),JSTRING,JSTRING);
        console.log("result is =>",result)
        console.log("result is ",Java.vm.getEnv().getStringUtfChars(result, null).readCString())
        result = Java.vm.getEnv().getStringUtfChars(result, null).readCString();
    })
    return result;
}

function invokemethod02(contents){
    var result = null;
    Java.perform(function(){    
        var JSTRING = NewStringUTF(Java.vm.getEnv(),Memory.allocUtf8String(contents))
        result = method02(Java.vm.getEnv(),JSTRING,JSTRING);
        result = Java.vm.getEnv().getStringUtfChars(result, null).readCString();
    })
    return result;
}
rpc.exports = {
    invoke1:invokemethod01,
    invoke2:invokemethod02
};
setImmediate(hook_RegisterNatives);

下面脚本自动Hook ART中关键符号，如GetStringUTFChars、NewStringUTF、FindClass、GetMethodID等，输出传参和返回值：

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/*
GetFieldID is at  0xe39b87c5 _ZN3art3JNI10GetFieldIDEP7_JNIEnvP7_jclassPKcS6_
GetMethodID is at  0xe39a1a19 _ZN3art3JNI11GetMethodIDEP7_JNIEnvP7_jclassPKcS6_
NewStringUTF is at  0xe39cff25 _ZN3art3JNI12NewStringUTFEP7_JNIEnvPKc
RegisterNatives is at  0xe39e08fd _ZN3art3JNI15RegisterNativesEP7_JNIEnvP7_jclassPK15JNINativeMethodi
GetStaticFieldID is at  0xe39c9635 _ZN3art3JNI16GetStaticFieldIDEP7_JNIEnvP7_jclassPKcS6_
GetStaticMethodID is at  0xe39be0ed _ZN3art3JNI17GetStaticMethodIDEP7_JNIEnvP7_jclassPKcS6_
GetStringUTFChars is at  0xe39d06e5 _ZN3art3JNI17GetStringUTFCharsEP7_JNIEnvP8_jstringPh
FindClass is at  0xe399ae5d _ZN3art3JNI9FindClassEP7_JNIEnvPKc
*/
function hook_libart() {
    var symbols = Module.enumerateSymbolsSync("libart.so");
    var addrGetStringUTFChars = null;
    var addrNewStringUTF = null;
    var addrFindClass = null;
    var addrGetMethodID = null;
    var addrGetStaticMethodID = null;
    var addrGetFieldID = null;
    var addrGetStaticFieldID = null;
    var addrRegisterNatives = null;
    for (var i = 0; i < symbols.length; i++) {
        var symbol = symbols[i];
        if (symbol.name.indexOf("art") >= 0 && symbol.name.indexOf("JNI") >= 0 && symbol.name.indexOf("CheckJNI") < 0) {
            if (symbol.name.indexOf("GetStringUTFChars") >= 0) {
                addrGetStringUTFChars = symbol.address;
                console.log("GetStringUTFChars is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("NewStringUTF") >= 0) {
                addrNewStringUTF = symbol.address;
                console.log("NewStringUTF is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("FindClass") >= 0) {
                addrFindClass = symbol.address;
                console.log("FindClass is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("GetMethodID") >= 0) {
                addrGetMethodID = symbol.address;
                console.log("GetMethodID is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("GetStaticMethodID") >= 0) {
                addrGetStaticMethodID = symbol.address;
                console.log("GetStaticMethodID is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("GetFieldID") >= 0) {
                addrGetFieldID = symbol.address;
                console.log("GetFieldID is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("GetStaticFieldID") >= 0) {
                addrGetStaticFieldID = symbol.address;
                console.log("GetStaticFieldID is at ", symbol.address, symbol.name);
            } else if (symbol.name.indexOf("RegisterNatives") >= 0) {
                addrRegisterNatives = symbol.address;
                console.log("RegisterNatives is at ", symbol.address, symbol.name);
            }
        }
    }
    if (addrGetStringUTFChars != null) {
        Interceptor.attach(addrGetStringUTFChars, {
            onEnter: function (args) { },
            onLeave: function (retval) {
                if (retval != null) {
                    var bytes = Memory.readCString(retval);
                    console.log("[GetStringUTFChars] result:" + bytes);
                    console.log('CCCryptorCreate called from:\n' + Thread.backtrace(this.context, Backtracer.FUZZY).map(DebugSymbol.fromAddress).join('\n') + '\n');
                }
            }
        });
    }
    if (addrNewStringUTF != null) {
        Interceptor.attach(addrNewStringUTF, {
            onEnter: function (args) {
                if (args[1] != null) {
                    var string = Memory.readCString(args[1]);
                    console.log("[NewStringUTF] bytes:" + string);
                }
            },
            onLeave: function (retval) { }
        });
    }
    if (addrFindClass != null) {
        Interceptor.attach(addrFindClass, {
            onEnter: function (args) {
                if (args[1] != null) {
                    var name = Memory.readCString(args[1]);
                    console.log("[FindClass] name:" + name);
                }
            },
            onLeave: function (retval) { }
        });
    }
    if (addrGetMethodID != null) {
        Interceptor.attach(addrGetMethodID, {
            onEnter: function (args) {
                if (args[2] != null) {
                    var name = Memory.readCString(args[2]);
                    if (args[3] != null) {
                        var sig = Memory.readCString(args[3]);
                        console.log("[GetMethodID] name:" + name + ", sig:" + sig);
                    } else {
                        console.log("[GetMethodID] name:" + name);
                    }
                }
            },
            onLeave: function (retval) { }
        });
    }
    if (addrGetStaticMethodID != null) {
        Interceptor.attach(addrGetStaticMethodID, {
            onEnter: function (args) {
                if (args[2] != null) {
                    var name = Memory.readCString(args[2]);
                    if (args[3] != null) {
                        var sig = Memory.readCString(args[3]);
                        console.log("[GetStaticMethodID] name:" + name + ", sig:" + sig);
                    } else {
                        console.log("[GetStaticMethodID] name:" + name);
                    }
                }
            },
            onLeave: function (retval) { }
        });
    }
    if (addrGetFieldID != null) {
        Interceptor.attach(addrGetFieldID, {
            onEnter: function (args) {
                if (args[2] != null) {
                    var name = Memory.readCString(args[2]);
                    if (args[3] != null) {
                        var sig = Memory.readCString(args[3]);
                        console.log("[GetFieldID] name:" + name + ", sig:" + sig);
                    } else {
                        console.log("[GetFieldID] name:" + name);
                    }
                }
            },
            onLeave: function (retval) { }
        });
    }
    if (addrGetStaticFieldID != null) {
        Interceptor.attach(addrGetStaticFieldID, {
            onEnter: function (args) {
                if (args[2] != null) {
                    var name = Memory.readCString(args[2]);
                    if (args[3] != null) {
                        var sig = Memory.readCString(args[3]);
                        console.log("[GetStaticFieldID] name:" + name + ", sig:" + sig);
                    } else {
                        console.log("[GetStaticFieldID] name:" + name);
                    }
                }
            },
            onLeave: function (retval) { }
        });
    }
    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);
                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));
                }
            },
            onLeave: function (retval) { }
        });
    }
}
setImmediate(hook_libart);

也可用jnitrace工具：

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jnitrace -l libroysue.so com.xxx.xxx