SO逆向入门实战教程十：SimpleSign

一、前言

这是系列的第十篇，通过该样本可以充分学习如何在Unidbg中补充环境。朋友zh3nu11和我共同完成了这篇内容，感谢。

二、准备

首先我们发现了init函数，它应该就是SO的初始化函数，其余的函数看名字也都很易懂。

三、Init 模拟执行

我们首先用Unidbg跑通Init初始化函数，先搭建基本框架

package com.article10;import com.github.unidbg.AndroidEmulator;
import com.github.unidbg.Module;
import com.github.unidbg.linux.android.AndroidEmulatorBuilder;
import com.github.unidbg.linux.android.AndroidResolver;
import com.github.unidbg.linux.android.dvm.AbstractJni;
import com.github.unidbg.linux.android.dvm.DalvikModule;
import com.github.unidbg.linux.android.dvm.VM;
import com.github.unidbg.memory.Memory;import java.io.File;public class SecurityUtil extends AbstractJni {private final AndroidEmulator emulator;private final VM vm;private final Module module;public SecurityUtil(){emulator = AndroidEmulatorBuilder.for32Bit().build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析vm = emulator.createDalvikVM(new File("base.apk"));DalvikModule dm = vm.loadLibrary(new File("libscmain.so"), true);module = dm.getModule();vm.setJni(this);vm.setVerbose(true);dm.callJNI_OnLoad(emulator);}public static void main(String[] args) {SecurityUtil test = new SecurityUtil();}
}

运行产生如下报错

红框即报错原因，内存错误，箭头所指是根本原因，样本中open了这两个文件，但找不到，所以我们需要补充这两个文件。

我们需要逐一做理解

1.proc/23638/xxx 是什么

proc 文件系统由内核提供，它是一个伪文件系统，它只存在内存当中，而不占用外存空间。它以文件系统的方式为访问系统内核数据的操作提供接口。系统中当前运行的每一个进程都有对应的一个目录在 proc 下，以进程的 PID 号为目录名，它们是读取进程信息的接口。

此处的23638就是Unidbg中APP的当前进程，每次运行，Unidbg都会随机化给一个进程PID，就像Linux系统中一样。

我修改了src/main/java/com/github/unidbg/AbstractEmulator.java 中的如图位置，使PID固定，因为PID不停变动可能会影响后续分析，但这不是必须的操作。

2.此处读取cmdline做什么

在Android系统中，进程的cmdline返回应用的进程名。那么此处的目的就很明显了，验证环境是否是”自己“的环境，防止应用被重打包。

3.在Unidbg中如何填补

proc 文件系统是伪文件系统，其目录下的所有文件，读写和正常文件没差别，所以在Unidbg中做好文件的重定向就行了。

三步走，实现IOResolver接口，注册接口，实现resolve方法并补充上我们的逻辑。

package com.article10;import com.github.unidbg.AndroidEmulator;
import com.github.unidbg.Emulator;
import com.github.unidbg.Module;
import com.github.unidbg.file.FileResult;
import com.github.unidbg.file.IOResolver;
import com.github.unidbg.linux.android.AndroidEmulatorBuilder;
import com.github.unidbg.linux.android.AndroidResolver;
import com.github.unidbg.linux.android.dvm.AbstractJni;
import com.github.unidbg.linux.android.dvm.DalvikModule;
import com.github.unidbg.linux.android.dvm.VM;
import com.github.unidbg.linux.file.ByteArrayFileIO;
import com.github.unidbg.memory.Memory;import java.io.File;public class SecurityUtil extends AbstractJni implements IOResolver {private final AndroidEmulator emulator;private final VM vm;private final Module module;public SecurityUtil(){emulator = AndroidEmulatorBuilder.for32Bit().build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分emulator.getSyscallHandler().addIOResolver(this);final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析vm = emulator.createDalvikVM(new File("base.apk"));DalvikModule dm = vm.loadLibrary(new File("libscmain.so"), true);module = dm.getModule();int pid = emulator.getPid();System.out.println("APP pid:"+pid);vm.setJni(this);vm.setVerbose(true);dm.callJNI_OnLoad(emulator);}public static void main(String[] args) {SecurityUtil test = new SecurityUtil();}@Overridepublic FileResult resolve(Emulator emulator, String pathname, int oflags) {if (("proc/"+emulator.getPid()+"/cmdline").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, "ctrip.android.view".getBytes()));}return null;}
}

那status呢？该文件包含该进程的众多信息：可执行文件名、当前状态、PID 和 PPID、实际及有效的 UID 和 GID、内存使用情况、以及其他。我们可以随便看一个

root@hammerhead:/proc/9884 # cat status
Name:   adb
State:  S (sleeping)
Tgid:   9884
Pid:    9884
PPid:   1
TracerPid:  0
Uid:    2000    2000    2000    2000
Gid:    2000    2000    2000    2000
FDSize: 32
Groups: 1003 1004 1007 1011 1015 1028 3001 3002 3003 3006
VmPeak:     4012 kB
VmSize:     2992 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:       880 kB
VmRSS:       880 kB
VmData:     1196 kB
VmStk:       136 kB
VmExe:       104 kB
VmLib:      1304 kB
VmPTE:         8 kB
VmSwap:        0 kB
Threads:    2
SigQ:   1/12274
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000001000
SigCgt: 000000000000a4f8
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: fffffff0000000c0
Cpus_allowed:   f
Cpus_allowed_list:  0-3
voluntary_ctxt_switches:    7
nonvoluntary_ctxt_switches: 46

一般而言，样本检测status是为了其中的TracerPid字段，TracerPid反调试的原理就是检测这个字段是否为0，为0说明没有被调试，不为0说明正在被调试，检测调试器直接退出就可以达到反调试的效果。

所以我们常常这么处理——只返回TracerPid字段

@Override
public FileResult resolve(Emulator emulator, String pathname, int oflags) {if (("proc/"+emulator.getPid()+"/cmdline").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, "ctrip.android.view".getBytes()));}if (("proc/" + emulator.getPid() + "/status").equals(pathname)) {return FileResult.<AndroidFileIO>success(new ByteArrayFileIO(oflags, pathname, "TracerPid:\t0\n".getBytes()));}return null;
}

有人可能会担心不保险，万一其他字段也被用到了呢，样本找不到这些字段导向错误逻辑怎么办？这个情况是存在的，我们马上就说，先运行看看效果，emm，似乎跑通了。

我们终于可以开始执行init函数了，但我打算先看看这个getNameByPid函数。

首先Frida Call 测试一下

function callgetPid(pid){var securityUtil = null;Java.perform(function () {Java.choose("ctrip.android.security.SecurityUtil", {//枚举时调用onMatch:function(instance){//打印实例securityUtil = instance;console.log("find instance")},//枚举完成后调用onComplete:function() {console.log("end")}});var result = securityUtil.getNameByPid(pid);console.log(result);})
}

看一下PID

结果是ip.android.view。Unidbg主动调用测试一下

package com.article10;import com.github.unidbg.AndroidEmulator;
import com.github.unidbg.Emulator;
import com.github.unidbg.Module;
import com.github.unidbg.file.FileResult;
import com.github.unidbg.file.IOResolver;
import com.github.unidbg.file.linux.AndroidFileIO;
import com.github.unidbg.linux.android.AndroidEmulatorBuilder;
import com.github.unidbg.linux.android.AndroidResolver;
import com.github.unidbg.linux.android.dvm.AbstractJni;
import com.github.unidbg.linux.android.dvm.DalvikModule;
import com.github.unidbg.linux.android.dvm.DvmObject;
import com.github.unidbg.linux.android.dvm.VM;
import com.github.unidbg.linux.file.ByteArrayFileIO;
import com.github.unidbg.memory.Memory;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;import java.io.File;
import java.util.ArrayList;
import java.util.List;public class SecurityUtil extends AbstractJni implements IOResolver {private final AndroidEmulator emulator;private final VM vm;private final Module module;public SecurityUtil(){emulator = AndroidEmulatorBuilder.for32Bit().build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分emulator.getSyscallHandler().addIOResolver(this);final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析vm = emulator.createDalvikVM(new File("base.apk"));DalvikModule dm = vm.loadLibrary(new File(libscmain.so"), true);module = dm.getModule();int pid = emulator.getPid();System.out.println("APP pid:"+pid);vm.setJni(this);vm.setVerbose(true);dm.callJNI_OnLoad(emulator);}public void callgetNameByPid(){List<Object> list = new ArrayList<>(10);list.add(vm.getJNIEnv());list.add(0);list.add(emulator.getPid());Number number = module.callFunction(emulator, 0xee01, list.toArray())[0];String name = vm.getObject(number.intValue()).getValue().toString();System.out.println(name);}public static void main(String[] args) {SecurityUtil test = new SecurityUtil();test.callgetNameByPid();}@Overridepublic FileResult resolve(Emulator emulator, String pathname, int oflags) {if (("proc/"+emulator.getPid()+"/cmdline").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, "ctrip.android.view".getBytes()));}if (("proc/" + emulator.getPid() + "/status").equals(pathname)) {return FileResult.<AndroidFileIO>success(new ByteArrayFileIO(oflags, pathname, "TracerPid:\t0\n".getBytes()));}return null;}
}

结果是0。实际上，这就是status 没补齐全带来的锅。这是APP真实的status

2|bullhead:/proc/19929 # cat status
Name:   ip.android.view
State:  R (running)
Tgid:   19929
Pid:    19929
PPid:   17506
TracerPid:      0
Uid:    10148   10148   10148   10148
Gid:    10148   10148   10148   10148
FDSize: 512
Groups: 3002 3003 9997 20148 50148
VmPeak:  2224800 kB
VmSize:  2180604 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:    354920 kB
VmRSS:    322600 kB
VmData:   375124 kB
VmStk:      8192 kB
VmExe:        20 kB
VmLib:    209888 kB
VmPTE:      2024 kB
VmSwap:     2952 kB
Threads:        122
SigQ:   2/6517
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000001204
SigIgn: 0000000000000000
SigCgt: 00000006400096fc
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000000000000000
CapAmb: 0000000000000000
Seccomp:        2
Cpus_allowed:   0f
Cpus_allowed_list:      0-3
Mems_allowed:   1
Mems_allowed_list:      0
voluntary_ctxt_switches:        123395
nonvoluntary_ctxt_switches:     84141

样本正是读取其中的Name，所以Unidbg补环境一定要心细和谨慎，处处可能出问题。看一下修改后的重定向方法

 @Overridepublic FileResult resolve(Emulator emulator, String pathname, int oflags) {if (("proc/"+emulator.getPid()+"/cmdline").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, "ctrip.android.view".getBytes()));}if (("proc/" + emulator.getPid() + "/status").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, ("Name:   ip.android.view\n" +"State:  R (running)\n" +"Tgid:   "+emulator.getPid()+"\n" +"Pid:    "+emulator.getPid()+"\n" +"PPid:   17506\n" +"TracerPid:      0\n" +"Uid:    10148   10148   10148   10148\n" +"Gid:    10148   10148   10148   10148\n" +"FDSize: 512\n" +"Groups: 3002 3003 9997 20148 50148\n" +"VmPeak:  2224800 kB\n" +"VmSize:  2185240 kB\n" +"VmLck:         0 kB\n" +"VmPin:         0 kB\n" +"VmHWM:    354920 kB\n" +"VmRSS:    324572 kB\n" +"VmData:   379340 kB\n" +"VmStk:      8192 kB\n" +"VmExe:        20 kB\n" +"VmLib:    209888 kB\n" +"VmPTE:      2020 kB\n" +"VmSwap:     3012 kB\n" +"Threads:        127\n" +"SigQ:   2/6517\n" +"SigPnd: 0000000000000000\n" +"ShdPnd: 0000000000000000\n" +"SigBlk: 0000000000001204\n" +"SigIgn: 0000000000000000\n" +"SigCgt: 00000006400096fc\n" +"CapInh: 0000000000000000\n" +"CapPrm: 0000000000000000\n" +"CapEff: 0000000000000000\n" +"CapBnd: 0000000000000000\n" +"CapAmb: 0000000000000000\n" +"Seccomp:        2\n" +"Cpus_allowed:   0f\n" +"Cpus_allowed_list:      0-3\n" +"Mems_allowed:   1\n" +"Mems_allowed_list:      0\n" +"voluntary_ctxt_switches:        21102\n" +"nonvoluntary_ctxt_switches:     20849").getBytes()));}return null;}

接下来步入正题——执行init方法！增改内容如下，并运行。

public void callInit(){List<Object> list = new ArrayList<>(10);list.add(vm.getJNIEnv());list.add(0);DvmObject<?> context = vm.resolveClass("android/content/Context").newObject(null);// contextlist.add(vm.addLocalObject(context));module.callFunction(emulator, 0x36a85, list.toArray());
};public static void main(String[] args) {SecurityUtil test = new SecurityUtil();test.callInit();
}

补JAVA环境是Unidbg中的基础活，但它是有技巧的，善用JNITrace可以补的又快又好，比如本篇的Unidbg环境，就是在1h内补好的。如果补环境有问题或者不会补，欢迎评论区或者课上交流讨论。

见招拆招补充几个后

    @Overridepublic DvmObject<?> callStaticObjectMethod(BaseVM vm, DvmClass dvmClass, String signature, VarArg varArg) {switch (signature) {case "android/os/Environment->getExternalStorageDirectory()Ljava/io/File;":{return vm.resolveClass("java/io/File").newObject(signature);}}return super.callStaticObjectMethod(vm, dvmClass, signature, varArg);}@Overridepublic DvmObject<?> callObjectMethod(BaseVM vm, DvmObject<?> dvmObject, String signature, VarArg varArg) {switch (signature) {case "java/io/File->getPath()Ljava/lang/String;":{System.out.println("PATH:"+dvmObject.getValue());if(dvmObject.getValue().equals("android/os/Environment->getExternalStorageDirectory()Ljava/io/File;")){return new StringObject(vm, "/mnt/sdcard");}if(dvmObject.getValue()=="android/content/Context->getFilesDir()Ljava/io/File;"){return new StringObject(vm, "/data/data/ctrip.android.view/files");}}case "android/content/Context->getPackageResourcePath()Ljava/lang/String;":return new StringObject(vm, "/data/app/ctrip.android.view-fM4xyjk_eygpJsiITNW4JA==/base.apk");case "android/content/Context->getFilesDir()Ljava/io/File;":return vm.resolveClass("java/io/File").newObject(signature);case "android/content/Context->getAssets()Landroid/content/res/AssetManager;":return new AssetManager(vm, signature);}return super.callObjectMethod(vm, dvmObject, signature, varArg);}

报错了，这次看不出啥明显错误
日志全开再看看，好像更迷糊了

但其实这个问题我们早就讲过了，Android中通过libandroid.so对Assets资源文件进行操作，日志中可以看到”getAssets“等字眼，但是由于libandroid.so的依赖SO太多了，Unidbg很难一一处理，所以资源文件相关的处理会报错。为此Unidbg做了一个折中的解决防范——可以自己注册虚拟模块，或者叫虚拟SO，libandroid.so已经由作者实现了，实现了常用的几个Assets操作的API。只用加上这一行就行，需要注意必须在样本SO之前加载或者叫注册进去

继续运行，为什么还报错

是这样的，样本在通过虚拟SO读取资源文件，资源的读取有四种模式

/** Available access modes for opening assets with {@link AAssetManager_open} */
enum {/** No specific information about how data will be accessed. **/AASSET_MODE_UNKNOWN      = 0,/** Read chunks, and seek forward and backward. */AASSET_MODE_RANDOM       = 1,/** Read sequentially, with an occasional forward seek. */AASSET_MODE_STREAMING    = 2,/** Caller plans to ask for a read-only buffer with all data. */AASSET_MODE_BUFFER       = 3
};

但作者只实现了模式1和2，而此处使用mode 0。mode 0 没有啥特殊处理要做，我们直接合并入mode 2和3的逻辑即可。

继续运行，即已经过了这个坑。有的人可能会困惑，Native层读写资源文件做什么？其实这是常见做法，比如把key编码进资源文件的一张图片里，Native层去读取这个资源文件获取key。

下面就是继续补JAVA环境，使用JNItrace辅助，飞速补完。

补完后代码整体长这样

package com.article10;import com.github.unidbg.AndroidEmulator;
import com.github.unidbg.Emulator;
import com.github.unidbg.Module;
import com.github.unidbg.file.FileResult;
import com.github.unidbg.file.IOResolver;
import com.github.unidbg.file.linux.AndroidFileIO;
import com.github.unidbg.linux.android.AndroidEmulatorBuilder;
import com.github.unidbg.linux.android.AndroidResolver;
import com.github.unidbg.linux.android.dvm.*;
import com.github.unidbg.linux.android.dvm.api.AssetManager;
import com.github.unidbg.linux.android.dvm.array.ByteArray;
import com.github.unidbg.linux.file.ByteArrayFileIO;
import com.github.unidbg.memory.Memory;
import com.github.unidbg.virtualmodule.android.AndroidModule;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;import java.io.File;
import java.util.ArrayList;
import java.util.List;public class SecurityUtil extends AbstractJni implements IOResolver {private final AndroidEmulator emulator;private final VM vm;private final Module module;public SecurityUtil(){emulator = AndroidEmulatorBuilder.for32Bit().build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分emulator.getSyscallHandler().addIOResolver(this);final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析vm = emulator.createDalvikVM(new File("base.apk"));new AndroidModule(emulator, vm).register(memory);DalvikModule dm = vm.loadLibrary(new File("libscmain.so"), true);module = dm.getModule();int pid = emulator.getPid();System.out.println("APP pid:"+pid);vm.setJni(this);vm.setVerbose(true);dm.callJNI_OnLoad(emulator);}public void callgetNameByPid(){List<Object> list = new ArrayList<>(10);list.add(vm.getJNIEnv());list.add(0);list.add(emulator.getPid());Number number = module.callFunction(emulator, 0xee01, list.toArray())[0];String name = vm.getObject(number.intValue()).getValue().toString();System.out.println(name);}public void callInit(){List<Object> list = new ArrayList<>(10);list.add(vm.getJNIEnv());list.add(0);DvmObject<?> context = vm.resolveClass("android/content/Context").newObject(null);// contextlist.add(vm.addLocalObject(context));module.callFunction(emulator, 0x36a85, list.toArray());};public static void main(String[] args) {Logger.getLogger("com.github.unidbg.linux.ARM32SyscallHandler").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.unix.UnixSyscallHandler").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.AbstractEmulator").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.linux.android.dvm.DalvikVM").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.linux.android.dvm.BaseVM").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.linux.android.dvm").setLevel(Level.DEBUG);SecurityUtil test = new SecurityUtil();test.callInit();}@Overridepublic DvmObject<?> callStaticObjectMethod(BaseVM vm, DvmClass dvmClass, String signature, VarArg varArg) {switch (signature) {case "android/os/Environment->getExternalStorageDirectory()Ljava/io/File;":{return vm.resolveClass("java/io/File").newObject(signature);}case "okio/zz->b(I)Ljava/lang/String;":{int key = varArg.getInt(0);switch (key){case 1:{return new StringObject(vm, "353626076466627");}case 0:{return new StringObject(vm, "8cff8823cf19b5ec");}case 101:{return new StringObject(vm, "25483");}case 103:{return new StringObject(vm, "1920*1080");}case 104:{return new StringObject(vm, "");}case 102:{return new StringObject(vm, "17637");}case 105:{return new StringObject(vm, "WIFI");}case 106:{return new StringObject(vm, "0.0.0.0:0");}case 8:{return new StringObject(vm, "0.0.0.0:0");}case 9:{return new StringObject(vm, "");}case 10:{return new StringObject(vm, "00:00:00:00:00:00");}case 107:{return new StringObject(vm, "[full-100]");}case 108:{return new StringObject(vm, "78");}}System.out.println("okio/zz->b(I) Key:"+key);}case "java/net/NetworkInterface->getByName(Ljava/lang/String;)Ljava/net/NetworkInterface;":{String name = null;DvmObject<?> namedvm = varArg.getObject(0);if(namedvm!=null){name = (String) namedvm.getValue();}return vm.resolveClass("java/net/NetworkInterface").newObject(name);}}return super.callStaticObjectMethod(vm, dvmClass, signature, varArg);}@Overridepublic DvmObject<?> callObjectMethod(BaseVM vm, DvmObject<?> dvmObject, String signature, VarArg varArg) {switch (signature) {case "java/io/File->getPath()Ljava/lang/String;":{System.out.println("PATH:"+dvmObject.getValue());if(dvmObject.getValue().equals("android/os/Environment->getExternalStorageDirectory()Ljava/io/File;")){return new StringObject(vm, "/mnt/sdcard");}if(dvmObject.getValue()=="android/content/Context->getFilesDir()Ljava/io/File;"){return new StringObject(vm, "/data/data/ctrip.android.view/files");}}case "android/content/Context->getPackageResourcePath()Ljava/lang/String;":return new StringObject(vm, "/data/app/ctrip.android.view-fM4xyjk_eygpJsiITNW4JA==/base.apk");case "android/content/Context->getFilesDir()Ljava/io/File;":return vm.resolveClass("java/io/File").newObject(signature);case "android/content/Context->getAssets()Landroid/content/res/AssetManager;":return new AssetManager(vm, signature);case "java/net/NetworkInterface->getHardwareAddress()[B":byte[] result = hexStringToByteArray("64BC0C65AA1E");return new ByteArray(vm, result);}return super.callObjectMethod(vm, dvmObject, signature, varArg);}public static byte[] hexStringToByteArray(String s) {int len = s.length();byte[] data = new byte[len / 2];for (int i = 0; i < len; i += 2) {data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)+ Character.digit(s.charAt(i+1), 16));}return data;}@Overridepublic FileResult resolve(Emulator emulator, String pathname, int oflags) {if (("proc/"+emulator.getPid()+"/cmdline").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, "ctrip.android.view".getBytes()));}if (("proc/" + emulator.getPid() + "/status").equals(pathname)) {return FileResult.success(new ByteArrayFileIO(oflags, pathname, ("Name:   ip.android.view\n" +"State:  R (running)\n" +"Tgid:   "+emulator.getPid()+"\n" +"Pid:    "+emulator.getPid()+"\n" +"PPid:   17506\n" +"TracerPid:      0\n" +"Uid:    10148   10148   10148   10148\n" +"Gid:    10148   10148   10148   10148\n" +"FDSize: 512\n" +"Groups: 3002 3003 9997 20148 50148\n" +"VmPeak:  2224800 kB\n" +"VmSize:  2185240 kB\n" +"VmLck:         0 kB\n" +"VmPin:         0 kB\n" +"VmHWM:    354920 kB\n" +"VmRSS:    324572 kB\n" +"VmData:   379340 kB\n" +"VmStk:      8192 kB\n" +"VmExe:        20 kB\n" +"VmLib:    209888 kB\n" +"VmPTE:      2020 kB\n" +"VmSwap:     3012 kB\n" +"Threads:        127\n" +"SigQ:   2/6517\n" +"SigPnd: 0000000000000000\n" +"ShdPnd: 0000000000000000\n" +"SigBlk: 0000000000001204\n" +"SigIgn: 0000000000000000\n" +"SigCgt: 00000006400096fc\n" +"CapInh: 0000000000000000\n" +"CapPrm: 0000000000000000\n" +"CapEff: 0000000000000000\n" +"CapBnd: 0000000000000000\n" +"CapAmb: 0000000000000000\n" +"Seccomp:        2\n" +"Cpus_allowed:   0f\n" +"Cpus_allowed_list:      0-3\n" +"Mems_allowed:   1\n" +"Mems_allowed_list:      0\n" +"voluntary_ctxt_switches:        21102\n" +"nonvoluntary_ctxt_switches:     20849").getBytes()));}return null;}
}

接下来遇到报错

样本在读取apk文件，继续在resolve方法中做好重定向的工作

     if (("/data/app/ctrip.android.view-fM4xyjk_eygpJsiITNW4JA==/base.apk").equals(pathname)) {return FileResult.success(new SimpleFileIO(oflags, new File("yourAPkpath\\xxx.apk"), pathname));}

继续运行，可能再补充一些JAVA环境，整体没有报错了，似乎init补充完了。

日志结尾看到样本对这些文件进行访问，虽然没有报错，但我们可能会好奇，它在做什么呢？事实上，如果存在这些文件，则说明手机已经Root，样本在试图访问这些文件，来判断系统是否被Root了。我们这里不做任何处理。

四、Unidbg 模拟执行SimpleSign

先Frida call一下，参数二固定，参数一可自行修改。

function callSimpleSign(){var securityUtil = null;Java.perform(function () {Java.choose("ctrip.android.security.SecurityUtil", {//枚举时调用onMatch:function(instance){//打印实例securityUtil = instance;console.log("find instance")},//枚举完成后调用onComplete:function() {console.log("end")}});var input1 = stringToBytes("7be9f13e7f5426d139cb4e5dbb1fdba7")var result = securityUtil.simpleSign(input1, "getdata");console.log(result);})
}

结果恒为75位长度，且相同输入也会有不同输出，原因未知。

接下来Unidbg中测试

    public void callSimpleSign(){List<Object> list = new ArrayList<>(10);list.add(vm.getJNIEnv());list.add(0);String input = "7be9f13e7f5426d139cb4e5dbb1fdba7";byte[] inputByte = input.getBytes(StandardCharsets.UTF_8);ByteArray inputByteArray = new ByteArray(vm,inputByte);list.add(vm.addLocalObject(inputByteArray));list.add(vm.addLocalObject(new StringObject(vm, "getdata")));Number number = module.callFunction(emulator, 0x80735, list.toArray())[0];System.out.println(vm.getObject(number.intValue()).getValue().toString());};public static void main(String[] args) {Logger.getLogger("com.github.unidbg.linux.ARM32SyscallHandler").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.unix.UnixSyscallHandler").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.AbstractEmulator").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.linux.android.dvm.DalvikVM").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.linux.android.dvm.BaseVM").setLevel(Level.DEBUG);Logger.getLogger("com.github.unidbg.linux.android.dvm").setLevel(Level.DEBUG);SecurityUtil test = new SecurityUtil();test.callInit();System.out.println("call SimpleSign");test.callSimpleSign();}

结果也很顺利，如果报错，则根据缺失的JAVA环境继续补即可。

考虑一个小问题，即使明文一致，结果也一直在变，这是为什么呢？有哪些原因可能导致这个结果呢？

五、尾声

相关程序和资料放群里，防止遇到恶意举报。