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----------------------//
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