自研Unidbg trace工具实战ollvm反混淆
上官雨宝2023-11-20 10:23:20
得益于Unicorn的强大的指令trace能力，可以很容易实现对cpu执行的每一条汇编指令的跟踪，进而对ollvm保护的函数进行剪枝，去掉虚假块，大大提高逆向分析效率。请分别使用Unidbg和Stalker引擎完成对该app中的jnicheck函数的trace跟踪，并简单分析该apk逻辑，找出flag。
首先是用unidbg简单的实现下调用。结果出现问题。
java.lang.IllegalStateException: Please vm.setJni(jni) at com.github.unidbg.linux.android.dvm.Hashable.checkJni(Hashable.java:8) at com.github.unidbg.linux.android.dvm.DvmClass.getStaticMethodID(DvmClass.java:101) at com.github.unidbg.linux.android.dvm.DalvikVM64$110.handle(DalvikVM64.java:1697)
很明显的提示让我们加上setJni。加上后，并且修改类继承自AbstractJni。然后再来一次。然后又出现错误。
JNIEnv->GetStaticMethodID(com/kanxue/crackme/MainActivity.crypt2(Ljava/lang/String;)Z) => 0xf66a2c58 was called from RX@0x40028d98[libnative-lib.so]0x28d98[23:35:36 063] WARN [com.github.unidbg.linux.ARM64SyscallHandler] (ARM64SyscallHandler:369) - handleInterrupt intno=2, NR=-129104, svcNumber=0x172, PC=unidbg@0xfffe07b4, LR=RX@0x400291c8[libnative-lib.so]0x291c8, syscall=nulljava.lang.UnsupportedOperationException: com/kanxue/crackme/MainActivity->crypt2(Ljava/lang/String;)Z at com.github.unidbg.linux.android.dvm.AbstractJni.callStaticBooleanMethodV(AbstractJni.java:169) at com.github.unidbg.linux.android.dvm.AbstractJni.callStaticBooleanMethodV(AbstractJni.java:164)
看着好像是没有找到这个静态函数的实现的样子。但是我测试，直接调用这个crypt2函数是没问题的。那么问题可能就是出在jni函数的内部调用jni函数了。然后既然我们已知直接调用crypt2没问题。实际上我们也可以直接调用crypt2来分析即可。但是既然是作业，那么还是跑通一下吧。那么我自己重写实现一下内部的调用。
@Override public boolean callStaticBooleanMethodV(BaseVM vm, DvmClass dvmClass, String signature, VaList vaList) { switch (signature){ case "com/kanxue/crackme/MainActivity->crypt2(Ljava/lang/String;)Z": Symbol symbol=module.findSymbolByName("Java_com_kanxue_crackme_MainActivity_crypt2"); StringObject str=vaList.getObjectArg(0); Number num=module.callFunction(emulator,symbol.getAddress(),str.toString()); return num.intValue()>0; } throw new UnsupportedOperationException(signature); }
然后又出现问题了。错误如下：
java.lang.IllegalStateException: running at com.github.unidbg.AbstractEmulator.emulate(AbstractEmulator.java:358) at com.github.unidbg.thread.Function64.run(Function64.java:39) at com.github.unidbg.thread.MainTask.dispatch(MainTask.java:19) at com.github.unidbg.thread.UniThreadDispatcher.run(UniThreadDispatcher.java:172)
大致意思就是虚拟机正在运行中，不能再调用另外一个jni函数。也就是说再callFunction中执行一个函数，实际就是开一个虚拟机去执行，然后因为这个虚拟机正在执行中，就不能调用另外一个函数。所以。我决定用两个虚拟机，就不会有问题啦。下面贴上完整代码。
package com.zuoye; import com.github.unidbg.AndroidEmulator;import com.github.unidbg.LibraryResolver;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.*;import com.github.unidbg.memory.Memory; import java.io.File; public class KanxueTest extends AbstractJni { private final AndroidEmulator emulator; private final VM vm; private final DvmClass mainActivityDvm; private final Module module; public static void main(String[] args) { KanxueTest bcfTest = new KanxueTest(); bcfTest.call_jnicheck(); } private KanxueTest(){ emulator = AndroidEmulatorBuilder .for64Bit() .build(); Memory memory = emulator.getMemory(); LibraryResolver resolver = new AndroidResolver(23); memory.setLibraryResolver(resolver); vm = emulator.createDalvikVM(); vm.setVerbose(true); vm.setJni(this); mainActivityDvm = vm.resolveClass("com/kanxue/crackme/MainActivity"); DalvikModule dm = vm.loadLibrary(new File("unidbg-android/src/test/resources/example_binaries/arm64-v8a/libnative-lib.so"), false); module=dm.getModule(); dm.callJNI_OnLoad(emulator); } @Override public boolean callStaticBooleanMethodV(BaseVM vm, DvmClass dvmClass, String signature, VaList vaList) { switch (signature){ case "com/kanxue/crackme/MainActivity->crypt2(Ljava/lang/String;)Z": StringObject input=vaList.getObjectArg(0); KanxueTest test2=new KanxueTest(); return test2.crypt2(input.getValue()); } throw new UnsupportedOperationException(signature); } //主动调用目标函数 private void call_jnicheck(){ Boolean res = mainActivityDvm.callStaticJniMethodBoolean(emulator, "jnicheck(Ljava/lang/String;)Z","aasd1123"); System.out.println(res); } private boolean crypt2(String data){ Boolean res = mainActivityDvm.callStaticJniMethodBoolean(emulator, "crypt2(Ljava/lang/String;)Z",data); return res; }}
这次就成功执行完成了，结果如下：
Find native function Java_com_kanxue_crackme_MainActivity_jnicheck => RX@0x40025904[libnative-lib.so]0x25904JNIEnv->GetStringUtfChars("aasd1123") was called from RX@0x400270a4[libnative-lib.so]0x270a4JNIEnv->NewStringUTF("aasd1123666") was called from RX@0x40027640[libnative-lib.so]0x27640JNIEnv->GetStringUtfChars("aasd1123666") was called from RX@0x400270a4[libnative-lib.so]0x270a4JNIEnv->FindClass(com/kanxue/crackme/MainActivity) was called from RX@0x40028008[libnative-lib.so]0x28008JNIEnv->GetStaticMethodID(com/kanxue/crackme/MainActivity.crypt2(Ljava/lang/String;)Z) => 0xf66a2c58 was called from RX@0x40028d98[libnative-lib.so]0x28d98Find native function Java_com_kanxue_crackme_MainActivity_crypt2 => RX@0x40029750[libnative-lib.so]0x29750JNIEnv->GetStringUtfChars(""aasd1123666"") was called from RX@0x400270a4[libnative-lib.so]0x270a4JNIEnv->CallStaticBooleanMethodV(class com/kanxue/crackme/MainActivity, crypt2("aasd1123666") => false) was called from RX@0x400291c8[libnative-lib.so]0x291c8false
接下来就是开启trace分析这个对比的逻辑，找到那个flag。
根据上面的日志，就可以看到实际上第一个函数就是讲字符串给加上666。
aasd1123 -> jnicheck -> aasd1123666 -> crypt2
所以关键是看crypt2的逻辑了。接着是对汇编执行对部分进行trace。这里我使用我之前写的trace方案。
https://github.com/dqzg12300/unidbg_tools.git
这里我自己封装了一套对trace的优化处理，能够打印ldr的内容。以及寄存器的详细变化。下面是调整后的代码。
//主动调用目标函数 private void call_jnicheck(){ KingTrace trace1=new KingTrace(emulator); //dump ldr的数据。包括ldr赋值给寄存器的如果是指针，也会dump GlobalData.is_dump_ldr=true; //dump str的数据 GlobalData.is_dump_str=true; trace1.initialize(0x40025904,0x40025904+0x162c,null); emulator.getBackend().hook_add_new(trace1,0x40025904,0x40025904+0x162c,emulator); Boolean res = mainActivityDvm.callStaticJniMethodBoolean(emulator, "jnicheck(Ljava/lang/String;)Z","XUe"); System.out.println(res); } private boolean crypt2(String data){ KingTrace trace1=new KingTrace(emulator); //dump ldr的数据。包括ldr赋值给寄存器的如果是指针，也会dump GlobalData.is_dump_ldr=true; //dump str的数据 GlobalData.is_dump_str=true; trace1.initialize(0x40029750,0x40029750+0x30c,null); emulator.getBackend().hook_add_new(trace1,0x40029750,0x40029750+0x30c,emulator); Boolean res = mainActivityDvm.callStaticJniMethodBoolean(emulator, "crypt2(Ljava/lang/String;)Z",data); return res; }
由于我们前面知道了处理后的字符串会固定带一个666.所以我在trace的数据里面直接找666.然后就找到了一段数据如下：
[22:53:56 379]ldr_left_address:bffff680 dump, md5=bff7dd55d78b9378f9b117f668e032f6, hex=616173643131323336363600000000000000000000000000000000000000000000000000000000000000000000000000size: 480000: 61 61 73 64 31 31 32 33 36 36 36 00 00 00 00 00 aasd1123666.....0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................^-----------------------------------------------------------------------------^[libnative-lib.so 0x297dc] [e04f00b9] 0x400297dc: "str w0, [sp, #0x4c]"-----w0=0xb sp=0xbffff5f0 //w0=0xb[libnative-lib.so 0x297e0] [e00308aa] 0x400297e0: "mov x0, x8"-----x0=0xb x8=0xbffff680 //x0=0xbffff680[libnative-lib.so 0x297e4] [ebe2ff97] 0x400297e4: "bl #0x40022390"[libnative-lib.so 0x297e8] [a00c0036] 0x400297e8: "tbz w0, #0, #0x4002997c"-----w0=0x0 //w0=0x0[libnative-lib.so 0x2997c] [e8031f2a] 0x4002997c: "mov w8, wzr"-----w8=0x0 //w8=0x0[libnative-lib.so 0x29980] [a8c31738] 0x40029980: "sturb w8, [x29, #-0x84]"-----w8=0x0 x29=0xbffff700 //w8=0x0
这里ldr拿到了我们入参到指针后，跳转到了22390这个位置的函数来处理。接下来我们把这个函数也trace一下。
private boolean crypt2(String data){ //dump ldr的数据。包括ldr赋值给寄存器的如果是指针，也会dump GlobalData.is_dump_ldr=true; //dump str的数据 GlobalData.is_dump_str=true; KingTrace trace1=new KingTrace(emulator); trace1.initialize(0x40029750,0x40029750+0x30c,null); emulator.getBackend().hook_add_new(trace1,0x40029750,0x40029750+0x30c,emulator); KingTrace trace2=new KingTrace(emulator); trace2.initialize(0x40022390,0x40022390+0x2574,null); emulator.getBackend().hook_add_new(trace2,0x40022390,0x40022390+0x2574,emulator); Boolean res = mainActivityDvm.callStaticJniMethodBoolean(emulator, "crypt2(Ljava/lang/String;)Z",data); return res;}
然后ida打开看一下这个函数里面的大致内容。然后发现里面调用了strcmp，这个很明显用来对比的函数，看下这个函数的地址如下：
这里说明调用FA0这个地址函数的，就是对比的函数，我们可以选择用unidbg来进行hook打印，也可以断点查入参数来查看，接着搜索一下trace的记录，发现这个函数调用只有一处。
[libnative-lib.so 0x22464] [a8035cf8] 0x40022464: "ldur x8, [x29, #-0x40]"-----x8=0x1 x29=0xbffff5e0 //x8=0xbffff140[libnative-lib.so 0x22468] [00011ff8] 0x40022468: "stur x0, [x8, #-0x10]"-----x0=0x40359000 x8=0xbffff140 //x0=0x40359000[libnative-lib.so 0x2246c] [490000d0] 0x4002246c: "adrp x9, #0x4002c000"-----x9=0x1 //x9=0x4002c000[libnative-lib.so 0x22470] [206540f9] 0x40022470: "ldr x0, [x9, #0xc8]"-----x0=0x40359000 x9=0x4002c000 //x0=0x40358000 >-----------------------------------------------------------------------------<[23:12:20 478]ldr_left_address:40358000 dump, md5=b9f0352c6f0897767968eee7fdbed86f, hex=5746566c4e6a593200000000000000000000000000000000000000000000000000000000000000000000000000000000size: 480000: 57 46 56 6C 4E 6A 59 32 00 00 00 00 00 00 00 00 WFVlNjY2........0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................^-----------------------------------------------------------------------------^[libnative-lib.so 0x22474] [01015ff8] 0x40022474: "ldur x1, [x8, #-0x10]"-----x1=0xb x8=0xbffff140 //x1=0x40359000[libnative-lib.so 0x22478] [ca7aff97] 0x40022478: "bl #0x40000fa0"[libnative-lib.so 0x2247c] [00000071] 0x4002247c: "subs w0, w0, #0"-----w0=0xffffffdf w0=0xffffffdf //w0=0xffffffdf
所以查一下这里进行对比的两个值，我是在调试中查看的，结果如下：
>-----------------------------------------------------------------------------<[23:13:25 680]x0=RW@0x40358000, md5=29dd7f057f3a9dda3b877e393e53b6da, hex=5746566c4e6a59320000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000size: 1120000: 57 46 56 6C 4E 6A 59 32 00 00 00 00 00 00 00 00 WFVlNjY2........0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................^-----------------------------------------------------------------------------^mx1 >-----------------------------------------------------------------------------<[23:13:27 638]x1=RW@0x40359000, md5=b500df35613831c3228d09ff59574abc, hex=5957467a5a4445784d6a4d324e6a593d000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000size: 1120000: 59 57 46 7A 5A 44 45 78 4D 6A 4D 32 4E 6A 59 3D YWFzZDExMjM2NjY=0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
看着是两个base64，转换一下后得到：
WFVlNjY2 -> XUe666YWFzZDExMjM2NjY= -> aasd1123666
那么这个结果就拿到了。直接用XUe来调用jnicheck函数，就成功了。
实际上这个结果我们用ida搜索666的字符串也是可以拿到的。不过我还是走一下分析的流程。
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stalker的部分，其实主要还是trace汇编记录出来，分析流程大致相同，而stalker早期我有进行工具的整合，处理过这一部分。我把当时写的部分拿贴一下吧。
//这个地方实际上是每个block触发的，所以我们在触发的时候，要把整个block内的指令全部传递给pyfunction stalkerTraceRange(tid, base, size) { Stalker.follow(tid, { transform: (iterator) => { const instruction = iterator.next(); const startAddress = instruction.address; const isModuleCode = startAddress.compare(base) >= 0 && startAddress.compare(base.add(size)) < 0; // const isModuleCode = true; //遍历出所有指令 do { iterator.keep(); if (isModuleCode) { //将指令传递给py var address=ptr(instruction["address"]-moduleBase); send({ type: 'inst', tid: tid, block: startAddress, val: JSON.stringify(instruction), jsname:"sktrace", moduleBase:moduleBase, address:address, }) //block执行结束后，再给python发个包通知下。 iterator.putCallout((context) => { var callOutAddress=ptr(context.pc-moduleBase) send({ type: 'ctx', tid: tid, val: JSON.stringify(context), jsname:"sktrace", moduleBase:moduleBase, address:callOutAddress }) }) } } while (iterator.next() !== null); // if(flag){ // send(data) // } } })} //对指定地址进行tracefunction traceAddr(addr) { let moduleMap = new ModuleMap(); let targetModule = moduleMap.find(addr); var msg=initMessage(); msg["data"]=JSON.stringify(targetModule); send(msg); let exports = targetModule.enumerateExports(); let symbols = targetModule.enumerateSymbols(); Interceptor.attach(addr, { onEnter: function(args) { this.tid = Process.getCurrentThreadId() // 这里两种模式，有一个是c的模式来处理，方便直接在js中对二进制进行输出打印。 // stalkerTraceRangeC(this.tid, targetModule.base, targetModule.size) // 这个模式是将结果传递到py里面进行输出 stalkerTraceRange(this.tid, targetModule.base, targetModule.size) }, onLeave: function(ret) { Stalker.unfollow(this.tid); Stalker.garbageCollect() send({ type: "fin", tid: this.tid, jsname:"sktrace" }) } })} //对指定符号函数，或者是指定地址进行tracefunction trace(symbol,offset){ const targetModule = Process.getModuleByName(libname); moduleBase=targetModule.base; let targetAddress = null; //如果填了符号函数名，就优先根据函数名查找地址 if(symbol.length>0) { targetAddress = targetModule.findExportByName(symbol); } else if(offset.length>0) { var offsetData=parseInt(offset,16); targetAddress = targetModule.base.add(ptr(offsetData)); } traceAddr(targetAddress)}
上面处理完了在js中获取每个block的指令，下面就是看py中如何处理解析这些指令进行打印。
def sktrace_message(self,p): # 根据我们上面定义的结构，逐步解析 if "data" in p: self.outlog(p["data"]) return optype=p["type"] # 如果这条推送数据是block中的指令 if optype=="inst": # print(p) inst=json.loads(p["val"]) address=int(p["address"],16) oplist=[] for opdata in inst["operands"]: if opdata["type"]=="reg": if opdata["value"] not in oplist: oplist.append(opdata["value"]) elif opdata["type"]=="mem": memdata=opdata["value"] if memdata["base"] not in oplist: oplist.append(memdata["base"]) enddata = "" for item in oplist: enddata+="%s={%s} "%(item,item) outdata="tid:%s address:%s %s %s\t\t//%s"%(str(p["tid"]),str(hex(address)),inst["mnemonic"],inst["opStr"],enddata) self.outlog(outdata) elif optype=="ctx": # 如果这个是当前block结束的通知 context=json.loads(p["val"]) address=int(p["address"],16) self.outlog("tid:" +str(p["tid"])+" address:"+str(hex(address))+" context:"+ p["val"]) else: self.outlog(json.dumps(p))
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