安卓 dex 通用脱壳技术研究（三）

http://my.oschina.net/cve2015/blog/508918

摘要  本文剖析安卓 Dalvik 解释器 Portable 的原理与实现，并通过修改 Dalvik 虚拟机实现 dex 文件的通用脱壳方案；本方法同样适应于 ART 虚拟机；

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/*      此为DexHunter实现的主要功能，进行内存dump，将class_def_items中dump出classdef和extra部分 */ void * DumpClass( void  *parament) {    while  (timer_flag) {        sleep(5);    }      DvmDex* pDvmDex=(( struct  arg*)parament)->pDvmDex;  //pDvmDex代表一个dex文件    Object *loader=(( struct  arg*)parament)->loader;    DexFile* pDexFile=pDvmDex->pDexFile;    MemMapping * mem=&pDvmDex->memMap;      u4  time =dvmGetRelativeTimeMsec();    ALOGI( "GOT IT begin: %d ms" , time );      char  *path =  new  char [100];    strcpy (path,dumppath);    strcat (path, "classdef" );   //构造classdef文件路径     FILE  *fp =  fopen (path,  "wb+" );      strcpy (path,dumppath);    strcat (path, "extra" );  //构造extra文件路径     FILE  *fp1 =  fopen (path, "wb+" );      uint32_t mask=0x3ffff;    char  padding=0;    const  char * header= "Landroid" ;    unsigned  int  num_class_defs=pDexFile->pHeader->classDefsSize;  //dex文件的Header域，class_defs_size，标示了class_def域有几个class_def_item    uint32_t total_pointer = mem->length-uint32_t(pDexFile->baseAddr-( const  u1*)mem->addr);    uint32_t rec=total_pointer;      while  (total_pointer&3) {        total_pointer++;    }      int  inc=total_pointer-rec;    uint32_t start = pDexFile->pHeader->classDefsOff+ sizeof (DexClassDef)*num_class_defs;    uint32_t end = (uint32_t)(( const  u1*)mem->addr+mem->length-pDexFile->baseAddr);      for  ( size_t  i=0;i<num_class_defs;i++)  //遍历所有class_def_item    {        bool  need_extra= false ;        ClassObject * clazz=NULL;        const  u1* data=NULL;        DexClassData* pData = NULL;        bool  pass= false ;        const  DexClassDef *pClassDef = dexGetClassDef(pDvmDex->pDexFile, i);        const  char  *descriptor = dexGetClassDescriptor(pDvmDex->pDexFile,pClassDef);          if (! strncmp (header,descriptor,8)||!pClassDef->classDataOff)        {            pass= true ;            goto  classdef;        }          clazz = dvmDefineClass(pDvmDex, descriptor, loader);   //First Step:class加载          if  (!clazz) {           continue ;        }          ALOGI( "GOT IT class: %s" ,descriptor);          if  (!dvmIsClassInitialized(clazz)) {   //Second Step:class初始化，遍历所有类进行初始化            if (dvmInitClass(clazz)){   //与dvmIsClassInitialized()函数共同完成初始化                ALOGI( "GOT IT init: %s" ,descriptor);            }        }                     if (pClassDef->classDataOff<start || pClassDef->classDataOff>end)        {            need_extra= true ;   //是不是需要extra这一块，当存在class_data_off不在dex范围内时，就需要        }          data=dexGetClassData(pDexFile, pClassDef);        pData = ReadClassData(&data);          if  (!pData) {            continue ;        }          if  (pData->directMethods) {            for  (uint32_t i=0; i<pData->header.directMethodsSize; i++) {                Method *method = &(clazz->directMethods[i]);                uint32_t ac = (method->accessFlags) & mask;                  ALOGI( "GOT IT direct method name %s.%s" ,descriptor,method->name);                  if  (!method->insns||ac&ACC_NATIVE) {                    if  (pData->directMethods[i].codeOff) {                        need_extra =  true ;                        pData->directMethods[i].accessFlags=ac;                        pData->directMethods[i].codeOff=0;                    }                    continue ;                }                  u4 codeitem_off = u4(( const  u1*)method->insns-16-pDexFile->baseAddr);                  if  (ac != pData->directMethods[i].accessFlags)                {                    ALOGI( "GOT IT method ac" );                    need_extra= true ;                    pData->directMethods[i].accessFlags=ac;                }                  if  (codeitem_off!=pData->directMethods[i].codeOff&&((codeitem_off>=start&&codeitem_off<=end)||codeitem_off==0)) {                    ALOGI( "GOT IT method code" );                    need_extra= true ;                    pData->directMethods[i].codeOff=codeitem_off;                }                  if  ((codeitem_off<start || codeitem_off>end) && codeitem_off!=0) {                    //如果code_item_off不在dex文件范围内，则写入extra; fp1为extra的句柄                    //这里使用的是slider.pptx，中的第二种方案，见p42                    need_extra= true ;                    pData->directMethods[i].codeOff = total_pointer;                    DexCode *code = (DexCode*)(( const  u1*)method->insns-16);                    uint8_t *item=(uint8_t *) code;                    int  code_item_len = 0;                    if  (code->triesSize) {                        const  u1 * handler_data = dexGetCatchHandlerData(code);                        const  u1** phandler=( const  u1**)&handler_data;                        uint8_t * tail=codeitem_end(phandler);                        code_item_len = ( int )(tail-item);                    } else {                        code_item_len = 16+code->insnsSize*2;                    }                      ALOGI( "GOT IT method code changed" );                      fwrite (item,1,code_item_len,fp1);                    fflush (fp1);                    total_pointer+=code_item_len;                    while  (total_pointer&3) {                        fwrite (&padding,1,1,fp1);                        fflush (fp1);                        total_pointer++;                    }                }            }        }          if  (pData->virtualMethods) {            for  (uint32_t i=0; i<pData->header.virtualMethodsSize; i++) {                Method *method = &(clazz->virtualMethods[i]);                uint32_t ac = (method->accessFlags) & mask;                  ALOGI( "GOT IT virtual method name %s.%s" ,descriptor,method->name);                  if  (!method->insns||ac&ACC_NATIVE) {                    if  (pData->virtualMethods[i].codeOff) {                        need_extra =  true ;                        pData->virtualMethods[i].accessFlags=ac;                        pData->virtualMethods[i].codeOff=0;                    }                    continue ;                }                  u4 codeitem_off = u4(( const  u1 *)method->insns - 16 - pDexFile->baseAddr);                  if  (ac != pData->virtualMethods[i].accessFlags)                {                    ALOGI( "GOT IT method ac" );                    need_extra= true ;                    pData->virtualMethods[i].accessFlags=ac;                }                  if  (codeitem_off!=pData->virtualMethods[i].codeOff&&((codeitem_off>=start&&codeitem_off<=end)||codeitem_off==0)) {                    ALOGI( "GOT IT method code" );                    need_extra= true ;                    pData->virtualMethods[i].codeOff=codeitem_off;                }                  if  ((codeitem_off<start || codeitem_off>end)&&codeitem_off!=0) {                    need_extra= true ;                    pData->virtualMethods[i].codeOff = total_pointer;                    DexCode *code = (DexCode*)(( const  u1*)method->insns-16);                    uint8_t *item=(uint8_t *) code;                    int  code_item_len = 0;                    if  (code->triesSize) {                        const  u1 *handler_data = dexGetCatchHandlerData(code);                        const  u1** phandler=( const  u1**)&handler_data;                        uint8_t * tail=codeitem_end(phandler);                        code_item_len = ( int )(tail-item);                    } else {                        code_item_len = 16+code->insnsSize*2;                    }                      ALOGI( "GOT IT method code changed" );                      fwrite (item,1,code_item_len,fp1);                    fflush (fp1);                    total_pointer+=code_item_len;                    while  (total_pointer&3) {                        fwrite (&padding,1,1,fp1);                        fflush (fp1);                        total_pointer++;                    }                }            }        }   classdef:         DexClassDef temp=*pClassDef;         uint8_t *p = (uint8_t *)&temp;           if  (need_extra) {             ALOGI( "GOT IT classdata before" );             int  class_data_len = 0;             uint8_t *out = EncodeClassData(pData,class_data_len);             if  (!out) {                 continue ;             }             temp.classDataOff = total_pointer;             fwrite (out,1,class_data_len,fp1);             fflush (fp1);             total_pointer+=class_data_len;             while  (total_pointer&3) {                 fwrite (&padding,1,1,fp1);                 fflush (fp1);                 total_pointer++;             }             free (out);             ALOGI( "GOT IT classdata written" );         } else {             if  (pData) {                 free (pData);             }         }           if  (pass) {             temp.classDataOff=0;             temp.annotationsOff=0;         }           ALOGI( "GOT IT classdef" );         fwrite (p,  sizeof (DexClassDef), 1, fp);         fflush (fp);    }      fclose (fp1);    fclose (fp);      //目前已经准备好了part1,classdef,data和extra 4部分文件    strcpy (path,dumppath);    strcat (path, "whole.dex" );  //组合4部分，并写入whole.dex    fp =  fopen (path, "wb+" );    rewind (fp);      int  fd=-1;    int  r=-1;    int  len=0;      char  *addr=NULL;    struct  stat st;      strcpy (path,dumppath);    strcat (path, "part1" );      fd=open(path,O_RDONLY,0666);    if  (fd==-1) {        return  NULL;    }      r=fstat(fd,&st);      if (r==-1){          close(fd);          return  NULL;    }      len=st.st_size;    addr=( char *)mmap(NULL,len,PROT_READ,MAP_PRIVATE,fd,0);    fwrite (addr,1,len,fp);    fflush (fp);    munmap(addr,len);    close(fd);      strcpy (path,dumppath);    strcat (path, "classdef" );      fd=open(path,O_RDONLY,0666);    if  (fd==-1) {        return  NULL;    }      r=fstat(fd,&st);      if (r==-1){          close(fd);          return  NULL;    }      len=st.st_size;    addr=( char *)mmap(NULL,len,PROT_READ,MAP_PRIVATE,fd,0);    fwrite (addr,1,len,fp);    fflush (fp);    munmap(addr,len);    close(fd);      strcpy (path,dumppath);    strcat (path, "data" );      fd=open(path,O_RDONLY,0666);    if  (fd==-1) {        return  NULL;    }      r=fstat(fd,&st);      if (r==-1){          close(fd);          return  NULL;    }      len=st.st_size;    addr=( char *)mmap(NULL,len,PROT_READ,MAP_PRIVATE,fd,0);    fwrite (addr,1,len,fp);    fflush (fp);    munmap(addr,len);    close(fd);      while  (inc>0) {        fwrite (&padding,1,1,fp);        fflush (fp);        inc--;    }      strcpy (path,dumppath);    strcat (path, "extra" );      fd=open(path,O_RDONLY,0666);    if  (fd==-1) {        return  NULL;    }      r=fstat(fd,&st);      if (r==-1){          close(fd);          return  NULL;    }      len=st.st_size;    addr=( char *)mmap(NULL,len,PROT_READ,MAP_PRIVATE,fd,0);    fwrite (addr,1,len,fp);    fflush (fp);    munmap(addr,len);    close(fd);      fclose (fp);    delete  path;      time =dvmGetRelativeTimeMsec();    ALOGI( "GOT IT end: %d ms" , time );      return  NULL; } //------------------------added end----------------------//