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[超长篇] Inject Your Code to a Portable Executable File

转至: http://www.codeguru.com/cpp/w-p/system/misc/article.php/c11393

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Windows NT 3.51 (I mean, Win3.1, Win95, Win98 were not perfect OSs). The MS-DOS data causes that your executable file to have the performance inside MS-DOS and the MS-DOS Stub program lets it display: "This program can not be run in MS-DOS mode" or "This program can be run only in Windows mode", or some things like these comments when you try to run a Windows EXE file inside MS-DOS 6.0, where there is no footstep of Windows. Thus, this data is reserved for the code to indicate these comments in the MS-DOS operating system. The most interesting part of the MS-DOS data is "MZ"! Can you believe, it refers to the name of "Mark Zbikowski", one of the first Microsoft programmers?

0 Preface

You might demand to comprehend the ways a virus program injects its procedure into the interior of a portable executable file and corrupts it, or you are interested in implementing a packer or a protector to encrypt the data of your portable executable (PE) file. This article is committed to represent a brief discussion to realize the performance that is accomplished by EXE tools or some kinds of mal-ware.

You can employ this article’s source code to create your custom EXE builder. It could be used to make an EXE protector in the right way, or with the wrong intention, to spread a virus. However, my purpose of writing this article has been the first application, so I will not be responsible for the immoral usage of these methods.

1 Prerequisites

There are no specific mandatory prerequisites to follow the topics in this article. If you are familiar with a debugger and also the portable file format, I suggest you to drop to Sections 2 and 3; the whole of these sections has been made for people who don’t have any knowledge regarding the EXE file format or debuggers.

2 Portable Executable File Format

The Portable Executable file format was defined to provide the best way for the Windows Operating System to execute code and also to store the essential data that is needed to run a program—for example constant data, variable data, import library links, and resource data. It consists of MS-DOS file information, Windows NT file information, Section Headers, and Section images, as shown in Table 1.

2.1 The MS-DOS data

These data let you remember the first days of developing the Windows Operating System. You were at the beginning of a way to achieve a complete Operating System such as

To me, only the offset of the PE signature in the MS-DOS data is important, so I can use it to find the position of the Windows NT data. I just recommend that you take a look at Table 1, and then observe the structure of IMAGE_DOS_HEADER in the <winnt.h> header in the <Microsoft Visual Studio .net path>\VC7\PlatformSDK\include\ folder or the <Microsoft Visual Studio 6.0 path>\VC98\include\ folder. I do not know why the Microsoft team has forgotten to provide some comment about this structure in the MSDN library!

typedef struct _IMAGE_DOS_HEADER { // DOS .EXE header "MZ"    WORD   e_magic;                // Magic number    WORD   e_cblp;                 // Bytes on last page of file    WORD   e_cp;                   // Pages in file    WORD   e_crlc;                 // Relocations    WORD   e_cparhdr;              // Size of header in                                   // paragraphs    WORD   e_minalloc;             // Minimum extra paragraphs                                   // needed    WORD   e_maxalloc;             // Maximum extra paragraphs                                   // needed    WORD   e_ss;                   // Initial (relative) SS                                   // value    WORD   e_sp;                   // Initial SP value    WORD   e_csum;                 // Checksum    WORD   e_ip;                   // Initial IP value    WORD   e_cs;                   // Initial (relative) CS                                   // value    WORD   e_lfarlc;               // File address of relocation                                   // table    WORD   e_ovno;                 // Overlay number    WORD   e_res[4];               // Reserved words    WORD   e_oemid;                // OEM identifier                                   // (for e_oeminfo)    WORD   e_oeminfo;              // OEM information;                                   // e_oemid specific    WORD   e_res2[10];             // Reserved words    LONG   e_lfanew;               // File address of the new                                   // exe header  } IMAGE_DOS_HEADER, *PIMAGE_DOS_HEADER;

e_lfanew is the offset that refers to the position of the Windows NT data. I have provided a program to obtain the header information from an EXE file and to display it to you. To use the program, just try:

PE Viewer

(Full Size Image)

(Full Size Image)

This sample is useful for the whole of this article.

Table 1: Portable Executable file format structure

00000000  ASCII "MZ"00000002  DW 009000000004  DW 000300000006  DW 000000000008  DW 00040000000A  DW 00000000000C  DW FFFF0000000E  DW 000000000010  DW 00B800000012  DW 000000000014  DW 000000000016  DW 000000000018  DW 00400000001A  DW 00000000001C  DB 00b&b&0000003B  DB 000000003C  DD 000000F0

00000040  ..B:..B4.C!B8\LC!This program canno00000060  t be run in DOS mode....$.......

000000F0  ASCII "PE"

000000F4  DW 014C000000F6  DW 0003000000F8  DD 3B7D8410000000FC  DD 0000000000000100  DD 0000000000000104  DW 00E000000106  DW 010F

00000108  DW 010B0000010A  DB 070000010B  DB 000000010C  DD 0001280000000110  DD 00009C0000000114  DD 0000000000000118  DD 000124750000011C  DD 0000100000000120  DD 0001400000000124  DD 0100000000000128  DD 000010000000012C  DD 0000020000000130  DW 000500000132  DW 000100000134  DW 000500000136  DW 000100000138  DW 00040000013A  DW 00000000013C  DD 0000000000000140  DD 0001F00000000144  DD 0000040000000148  DD 0001D7FC0000014C  DW 00020000014E  DW 800000000150  DD 0004000000000154  DD 0000100000000158  DD 001000000000015C  DD 0000100000000160  DD 0000000000000164  DD 00000010

000001E8  ASCII".text"000001F0  DD 000126B0000001F4  DD 00001000000001F8  DD 00012800000001FC  DD 0000040000000200  DD 0000000000000204  DD 0000000000000208  DW 00000000020A  DW 00000000020C  DD 60000020    CODE|EXECUTE|READ

00000210  ASCII".data"; SECTION00000218  DD 0000101C ; VirtualSize = 0x101C0000021C  DD 00014000 ; VirtualAddress = 0x1400000000220  DD 00000A00 ; SizeOfRawData = 0xA0000000224  DD 00012C00 ; PointerToRawData = 0x12C0000000228  DD 00000000 ; PointerToRelocations = 0x00000022C  DD 00000000 ; PointerToLineNumbers = 0x000000230  DW 0000     ; NumberOfRelocations = 0x000000232  DW 0000     ; NumberOfLineNumbers = 0x000000234  DD C0000040 ; Characteristics =                        INITIALIZED_DATA|READ|WRITE00000238  ASCII".rsrc"; SECTION00000240  DD 00008960 ; VirtualSize = 0x896000000244  DD 00016000 ; VirtualAddress = 0x1600000000248  DD 00008A00 ; SizeOfRawData = 0x8A000000024C  DD 00013600 ; PointerToRawData = 0x1360000000250  DD 00000000 ; PointerToRelocations = 0x000000254  DD 00000000 ; PointerToLineNumbers = 0x000000258  DW 0000     ; NumberOfRelocations = 0x00000025A  DW 0000     ; NumberOfLineNumbers = 0x00000025C  DD 40000040 ; Characteristics =                        INITIALIZED_DATA|READ

00000400  EA 22 DD 77 D7 23 DD 77  C*"C.wC.#C.w00000408  9A 18 DD 77 00 00 00 00  E!.C.w....00000410  2E 1E C7 77 83 1D C7 77  ..C.wF..C.w00000418  FF 1E C7 77 00 00 00 00  C?.C.w....00000420  93 9F E7 77 D8 05 E8 77  b.E8C'wC..C(w00000428  FD A5 E7 77 AD A9 E9 77  C=B%C'w­B)C)w00000430  A3 36 E7 77 03 38 E7 77  B#6C'w.8C'w00000438  41 E3 E6 77 60 8D E7 77  AC#C&w`BC'w00000440  E6 1B E6 77 2B 2A E7 77  C&.C&w+*C'w00000448  7A 17 E6 77 79 C8 E6 77  z.C&wyC.C&w00000450  14 1B E7 77 C1 30 E7 77  ..C'wC.0C'wb&

b&0001BF00  63 00 2E 00 63 00 68 00  c...c.h.0001BF08  6D 00 0A 00 43 00 61 00  m...C.a.0001BF10  6C 00 63 00 75 00 6C 00  l.c.u.l.0001BF18  61 00 74 00 6F 00 72 00  a.t.o.r.0001BF20  11 00 4E 00 6F 00 74 00  ..N.o.t.0001BF28  20 00 45 00 6E 00 6F 00   .E.n.o.0001BF30  75 00 67 00 68 00 20 00  u.g.h. .0001BF38  4D 00 65 00 6D 00 6F 00  M.e.m.o.0001BF40  72 00 79 00 00 00 00 00  r.y.....0001BF48  00 00 00 00 00 00 00 00  ........0001BF50  00 00 00 00 00 00 00 00  ........0001BF58  00 00 00 00 00 00 00 00  ........0001BF60  00 00 00 00 00 00 00 00  ........0001BF68  00 00 00 00 00 00 00 00  ........0001BF70  00 00 00 00 00 00 00 00  ........0001BF78  00 00 00 00 00 00 00 00  ........

2.2 The Windows NT data

As mentioned in the preceding section, e_lfanew storage in the MS-DOS data structure refers to the location of the Windows NT information. Hence, if you assume that the pMem pointer relates the start point of the memory space for a selected portable executable file, you can retrieve the MS-DOS header and also the Windows NT headers by the following lines, which you also can perceive in the PE viewer sample (pelib.cpp, PEStructure::OpenFileName()):

IMAGE_DOS_HEADER        image_dos_header;IMAGE_NT_HEADERS        image_nt_headers;PCHAR pMem;b&memcpy(&image_dos_header, pMem,       sizeof(IMAGE_DOS_HEADER));memcpy(&image_nt_headers,       pMem+image_dos_header.e_lfanew,       sizeof(IMAGE_NT_HEADERS));

IMAGE_NT_HEADERS structure definition. It makes it possible to grasp what the image NT header maintains to execute a code inside the Windows NT OS. Now, you are conversant with the Windows NT structure; it consists of the "PE" Signature, the File Header, and the Optional Header. Do not forget to take a glimpse at their comments in the MSDN Library and in Table 1.

It seems to be very simple, the retrieval of the headers information. I recommend inspecting the MSDN library regarding the

One the whole, I consider merely, in most circumstances, the following cells of the IMAGE_NT_HEADERS structure:

FileHeader->NumberOfSectionsOptionalHeader->AddressOfEntryPointOptionalHeader->ImageBaseOptionalHeader->SectionAlignmentOptionalHeader->FileAlignmentOptionalHeader->SizeOfImageOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]              ->VirtualAddressOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]              ->Size

You can observe the main purpose of these values clearly, and their role when the internal virtual memory space allocated for an EXE file by the Windows task manager if you pay attention to their explanations in MSDN library, so I am not going to repeat the MSDN annotations here.

I should make a brief comment regarding the PE data directories, or OptionalHeader-> DataDirectory[], because I think there are a few aspects of interest concerning them. When you come to survey the Optional header through the Windows NT information, you will find that there are 16 directories at the end of the Optional Header, where you can find the consecutive directories, including their Relative Virtual Address and Size. I just mention here the notes from <winnt.h> to clarify these information:

// Export Directory#define IMAGE_DIRECTORY_ENTRY_EXPORT          0// Import Directory#define IMAGE_DIRECTORY_ENTRY_IMPORT          1// Resource Directory#define IMAGE_DIRECTORY_ENTRY_RESOURCE        2// Exception Directory#define IMAGE_DIRECTORY_ENTRY_EXCEPTION       3// Security Directory#define IMAGE_DIRECTORY_ENTRY_SECURITY        4// Base Relocation Table#define IMAGE_DIRECTORY_ENTRY_BASERELOC       5// Debug Directory#define IMAGE_DIRECTORY_ENTRY_DEBUG           6// Architecture Specific Data#define IMAGE_DIRECTORY_ENTRY_ARCHITECTURE    7// RVA of GP#define IMAGE_DIRECTORY_ENTRY_GLOBALPTR       8// TLS Directory#define IMAGE_DIRECTORY_ENTRY_TLS             9// Load Configuration Directory#define IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG    10// Bound Import Directory in headers#define IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT   11// Import Address Table#define IMAGE_DIRECTORY_ENTRY_IAT            12// Delay Load Import Descriptors#define IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT   13// COM Runtime descriptor#define IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR 14

The last one (15) was reserved for use in the future; I have not yet seen any purpose for it, even in PE64.

For instance, if you want to perceive the relative virtual address (RVA) and the size of the resource data, it is enough to retrieve them by:

DWORD dwRVA  = image_nt_headers.OptionalHeader->   DataDirectory[IMAGE_DIRECTORY_ENTRY_RESOURCE]->VirtualAddress;DWORD dwSize = image_nt_headers.OptionalHeader->   DataDirectory[IMAGE_DIRECTORY_ENTRY_RESOURCE]->Size;

To comprehend more regarding the significance of data directories, I forward you to Section 3.4.3 of the Microsoft Portable Executable and the Common Object File Format Specification document by Microsoft, and furthermore Section 6 of this document, where you discern the various types of sections and their applications. You will see the section’s advantage subsequently.

2.3 The Section Headers and Sections

You currently observe how the portable executable files declare the location and the size of a section on a disk storage file and inside the virtual memory space allocated for the program with IMAGE_NT_HEADERS-> OptionalHeader->SizeOfImage by the Windows task manager, as well the characteristics to demonstrate the type of the section. To better understand the Section header as my previous declaration, I suggest having a brief look at the IMAGE_SECTION_HEADER structure definition in the MSDN library. For an EXE packer developer, VirtualSize, VirtualAddress, SizeOfRawData, PointerToRawData, and Characteristics cells have significant rules. When developing an EXE packer, you should be clever enough to play with them. There are somet hings to note when you modify them; you should take care to align the VirtualSize and VirtualAddress according to OptionalHeader->SectionAlignment, as well as SizeOfRawData and PointerToRawData in line with OptionalHeader->FileAlignment. Otherwise, you will corrupt your target EXE file and it will never run. Regarding Characteristics, I pay attention mostly to establish a section by IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_CNT_INITIALIZED_DATA, I prefer that my new section has the ability to initialize such data during the running process, such as import table; besides, I need it to be able to modify itself by the loader with my settings in the section characteristics to read- and writeable.

Moreover, you should pay attention to the section names; you can know the purpose of each section by its name. I will just forward you to Section 6 of the Microsoft Portable Executable and the Common Object File Format Specification documents. I believe it represents the totality of sections by their names; this is also included in Table 2.

Table 2: Section names

To comprehend the section headers and also the sections, you can run the sample PE viewer. With this PE viewer, you can realize only the application of the section headers in a file image, so to observe the main significance in the Virtual Memory, you should try to load a PE file by a debugger. The next section represents the main idea of using the virtual address and size in the virtual memory by using a debugger. The last note is about IMAGE_NT_HEADERS-> FileHeader->NumberOfSections, that provides a number of sections in a PE file. Do not forget to adjust it whenever you remove or add some sections to a PE file. I am talking about section injection!

3 Debugger, Disassembler and some Useful Tools

In this part, you will become familiar with the necessary and essential equipment to develop your PE tools.

3.1 Debuggers

The first essential prerequisite to become a PE tools developer is to have enough experience with bug tracer tools. Furthermore, you should know most of the assembly instructions. To me, the Intel documents are the best references. You can obtain them from the Intel site for IA-32, and on top of that IA-64; the future belongs to IA-64 CPUs, Windows XP 64-bit, and also PE64!

• IA-32 Intel Architecture Software Developer’s Manuals
• Intel Itanium Architecture Assembly Language Reference Guide
• The Intel Itanium Processor Developer Resource Guide

To trace a PE file, SoftICE by Compuware Corporation, I knew it also as named NuMega when I was at high school, is the best debugger in the world. It implements process tracing by using the kernel mode method debugging without applying Windows debugging application programming interface (API) functions. In addition, I will introduce one perfect debugger in user mode level. It utilizes the Windows debugging API to trace a PE file and also attaches itself to an active process. These API functions have been provided by Microsoft teams, inside the Windows Kernel32 library, to trace a specific process, by using Microsoft tools, or perhaps, to make your own debugger! Some of those API functions inlude:

• CreateThread()
• CreateProcess()
• OpenProcess()
• DebugActiveProcess()
• GetThreadContext()
• SetThreadContext()
• ContinueDebugEvent()
• DebugBreak()
• ReadProcessMemory()
• WriteProcessMemory()
• SuspendThread()
• ResumeThread()

3.1.1 SoftICE

It was in 1987; Frank Grossman and Jim Moskun decided to establish a company called NuMega Technologies in Nashua, NH, to develop some equipment to trace and test the reliability of Microsoft Windows software programs. Now, it is a part of Compuware Corporation and its product has participated to accelerate the reliability in Windows software, and additionally in Windows driver developments. Currently, everyone knows the Compuware DriverStudio that is used to establish an environment for implementing the elaboration of a kernel driver or a system file by aiding the Windows Driver Development Kit (DDK). It bypasses the involvement of DDK to implement a portable executable file of kernel level for a Windows system software developer. For us, only one instrument of DriverStudio is important, SoftICE; this debugger can be used to trace every portable executable file, a PE file for user mode level or a PE file for kernel mode level.

Figure 1: SoftICE Window

3.1.2 OllyDbg

It was about four years ago that I first saw this debugger by chance. For me, it was the best choice; I was not wealthy enough to purchase SoftICE, and at that time, SoftICE only had good functions for DOS, Windows 98, and Windows 2000. I found that this debugger supported all kinds of Windows versions. Therefore, I started to learn it very fast, and now it is my favorite debugger for the Windows OS. It is a debugger that can be used to trace all kinds of portable executable files except a Common Language Infrastructure (CLI) file format in user mode level, by using the Windows debugging API. Oleh Yuschuk, the author, is one of worthiest software developers I have seen in my life. He is a Ukrainian who now lives in Germany. I should mention here that his debugger is the best choice for hacker and cracker parties around the world! It is freeware! You can try it from the OllyDbg Homepage.

Figure 2: OllyDbg CPU Window

Proview or PVDasm is an admirable disassembler by the Reverse-Engineering-Community; it is still under development and bug fixing. You can find its disassmbler source engine and employ it to create your own disassembler.

3.2.2 W32Dasm

W32DASM can disassemble both 16- and 32-bit executable file formats. In addition to its disassembling ability, you can employ it to analyze import, export, and resource data directories data.

3.2.3 IDA Pro

All reverse-engineering experts know that IDA Pro can be used to investigate, not only x86 instructions, but that of various kinds of CPU types like AVR, PIC, and so forth. It can illustrate the assembly source of a portable executable file by using colored graphics and tables, and is very useful for any newbie in this area. Furthermore, it has the capability to trace an executable file inside the user mode level in the same way as OllyDbg.

3.3 Some Useful Tools

A good PE tools developer is conversant with the tools that save his time, so I recommend that you select some appropriate instruments to investigate the base information under a portable executable file.

3.3.1 LordPE

LordPE by y0da is still the first choice to retrieve PE file information with the possibility to modify them.

3.3.2 PEiD

PE iDentifier is valuable to identify the type of compilers, packers, and cryptors of PE files. As of now, it can detect more than 500 different signature types of PE files.

3.3.3 Resource Hacker

Resource Hacker can be employed to modify resource directory information; icon, menu, version info, string table, and so on.

3.3.4 WinHex

WinHex, it is clear what you can do with this tool.

3.3.5 CFF Explorer

Eventually, CFF Explorer by Ntoskrnl is what you want to have as a PE Utility tool in your arsenal; it supports PE32/64, PE rebuild included Common Language Infrastructure (CLI) file. In other words, the .NET file, a resource modifier, and much more facilities which can not be found in others. Just try to discover every unimaginable option by hand.

4 Add a New Section and Change the OEP

You are ready to do the first step of making your project. I have provided a library to add a new section and rebuild the portable executable file. Before starting, I wnat you to get familiar with the headers of a PE file, by using OllyDbg. You should first open a PE file; that pops up a menu, View->Executable file. Again, you get a popup menu: Special->PE header. You will observe a scene similar to Figure 3. Now, come to the Main Menu View->Memory, and try to distinguish the sections inside the Memory map window.

Figure 3

00000000000000020000000400000006000000080000000A0000000C0000000E00000010000000120000001400000016000000180000001A0000001C0000001D0000001E0000001F000000200000002100000022000000230000002400000025000000260000002700000028000000290000002A0000002B0000002C0000002D0000002E0000002F000000300000003100000032000000330000003400000035000000360000003700000038000000390000003A0000003B0000003C

 4D 5A 9000 0300 0000 0400 0000 FFFF 0000 B800 0000 0000 0000 4000 0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 F0000000

 ASCII "MZ" DW 0090 DW 0003 DW 0000 DW 0004 DW 0000 DW FFFF DW 0000 DW 00B8 DW 0000 DW 0000 DW 0000 DW 0040 DW 0000 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DB 00 DD 000000F0

 DOS EXE Signature DOS_PartPag = 90 (144.) DOS_PageCnt = 3 DOS_ReloCnt = 0 DOS_HdrSize = 4 DOS_MinMem = 0 DOS_MaxMem = FFFF (65535.) DOS_ReloSS = 0 DOS_ExeSP = B8 DOS_ChkSum = 0 DOS_ExeIP = 0 DOS_ReloCS = 0 DOS_TablOff = 40 DOS_Overlay = 0 Offset to PE signature

I want to explain how you can plainly change the Offset of Entry Point (OEP) in your sample file, CALC.EXE of Windows XP. First, by using a PE Tool, and also using your PE Viewer, you find OEP, 0x00012475, and Image Base, 0x01000000. This value of OEP is the Relative Virtual Address, so the Image Base value is used to convert it to the Virtual Address.

DWORD OEP_RVA = image_nt_headers->   OptionalHeader.AddressOfEntryPoint ;// OEP_RVA = 0x00012475DWORD OEP_VA = image_nt_headers->   OptionalHeader.ImageBase + OEP_RVA ;// OEP_VA = 0x01000000 + 0x00012475 = 0x01012475

__stdcall void DynLoader(){_asm{//----------------------------------    DWORD_TYPE(DYN_LOADER_START_MAGIC)//----------------------------------    MOV EAX,01012475h // << Original OEP    JMP EAX//----------------------------------    DWORD_TYPE(DYN_LOADER_END_MAGIC)//----------------------------------}}

//----------------------------------------------------------------class CPELibrary{private:    //-----------------------------------------    PCHAR                   pMem;    DWORD                   dwFileSize;    //-----------------------------------------protected:    //-----------------------------------------    PIMAGE_DOS_HEADER       image_dos_header;    PCHAR                   pDosStub;    DWORD                   dwDosStubSize, dwDosStubOffset;    PIMAGE_NT_HEADERS       image_nt_headers;    PIMAGE_SECTION_HEADER   image_section_header[MAX_SECTION_NUM];    PCHAR                   image_section[MAX_SECTION_NUM];    //-----------------------------------------protected:    //-----------------------------------------    DWORD PEAlign(DWORD dwTarNum,DWORD dwAlignTo);    void AlignmentSections();    //-----------------------------------------    DWORD Offset2RVA(DWORD dwRO);    DWORD RVA2Offset(DWORD dwRVA);    //-----------------------------------------    PIMAGE_SECTION_HEADER ImageRVA2Section(DWORD dwRVA);    PIMAGE_SECTION_HEADER ImageOffset2Section(DWORD dwRO);    //-----------------------------------------    DWORD ImageOffset2SectionNum(DWORD dwRVA);    PIMAGE_SECTION_HEADER AddNewSection(char* szName,DWORD dwSize);    //-----------------------------------------public:    //-----------------------------------------    CPELibrary();    ~CPELibrary();    //-----------------------------------------    void OpenFile(char* FileName);    void SaveFile(char* FileName);    //-----------------------------------------};

4.2 Create data for the new section

Full Size Image)

You can comprehend the difference between incremental link and no-incremental link by looking at the following picture:

To acquire the virtual address of DynLoader(), you obtain the virtual address of JMP pemaker.DynLoader in the incremental link, but by no-incremental link, the real virtual address is gained by the following code:

DWORD dwVA= (DWORD) DynLoader;

This setting is more critical in the incremental link when you try to find the beginning and ending of the Loader, DynLoader(), by CPECryptor::ReturnToBytePtr():

void* CPECryptor::ReturnToBytePtr(void* FuncName, DWORD findstr){    void* tmpd;    __asm   {        mov eax, FuncName        jmp dfhjg:    inc eaxdf:     mov ebx, [eax]        cmp ebx, findstr        jnz hjg        mov tmpd, eax    }    return tmpd;}

In pecrypt.cpp, I have represented another class, CPECryptor, to comprise the data of the new section. Nevertheless, the data of the new section is created by DynLoader() in loader.cpp, DynLoader Step 1. You use the CPECryptor class to enter this data in to the new section, and also some other stuff.

CPECryptor Class Step 1

//----------------------------------------------------------------class CPECryptor: public CPELibrary{private:    //----------------------------------------    PCHAR pNewSection;    //----------------------------------------    DWORD GetFunctionVA(void* FuncName);    void* ReturnToBytePtr(void* FuncName, DWORD findstr);    //----------------------------------------protected:    //----------------------------------------public:    //----------------------------------------    void CryptFile(int(__cdecl *callback) (unsigned int,                                           unsigned int));    //----------------------------------------};//----------------------------------------------------------------

4.3 Some notes regarding creating a new PE file

• Align the VirtualAddress and the VirtualSize of each section by SectionAlignment:

  image_section_header[i]->VirtualAddress=    PEAlign(image_section_header[i]->VirtualAddress,    image_nt_headers->OptionalHeader.SectionAlignment);image_section_header[i]->Misc.VirtualSize=    PEAlign(image_section_header[i]->Misc.VirtualSize,    image_nt_headers->OptionalHeader.SectionAlignment);

• Align the PointerToRawData and the SizeOfRawData of each section by FileAlignment:

  image_section_header[i]->PointerToRawData =    PEAlign(image_section_header[i]->PointerToRawData,            image_nt_headers->OptionalHeader.FileAlignment);image_section_header[i]->SizeOfRawData =    PEAlign(image_section_header[i]->SizeOfRawData,            image_nt_headers->OptionalHeader.FileAlignment);

• Correct the SizeofImage by the virtual size and the virtual address of the last section:

  image_nt_headers->OptionalHeader.SizeOfImage =   image_section_header[LastSection]->VirtualAddress +   image_section_header[LastSection]->Misc.VirtualSize;

• Set the Bound Import Directory header to zero because this directory is not very important to execute a PE file:

  image_nt_headers->   OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT].  VirtualAddress = 0;image_nt_headers->   OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_BOUND_                                IMPORT].Size = 0;

4.4 Some notes regarding linking this VC Project

• Set Linker->General->Enable Incremental Linking to No (/INCREMENTAL:NO).

  
  (

5 Store Important Data and Reach the Original OEP

Right now, we save the Original OEP and also the Image Base in order to reach to the virtual address of OEP. I have reserved a free space at the end of DynLoader() to store them, DynLoader Step 2.

PE Maker – Step 2

Download the pemaker2.zip source files from the end of the article.

DynLoader Step 2

__stdcall void DynLoader(){_asm{//------------------------------------    DWORD_TYPE(DYN_LOADER_START_MAGIC)//------------------------------------Main_0:    PUSHAD    // get base ebp    CALL Main_1Main_1:    POP EBP    SUB EBP,OFFSET Main_1    MOV EAX,DWORD PTR [EBP+_RO_dwImageBase]    ADD EAX,DWORD PTR [EBP+_RO_dwOrgEntryPoint]    PUSH EAX    RETN // >> JMP to Original OEP//----------------------------------    DWORD_TYPE(DYN_LOADER_START_DATA1)//----------------------------------//----------------------------------    DWORD_TYPE(DYN_LOADER_END_MAGIC)//----------------------------------}}_RO_dwImageBase:                DWORD_TYPE(0xCCCCCCCC)_RO_dwOrgEntryPoint:            DWORD_TYPE(0xCCCCCCCC)

The new function, CPECryptor::CopyData1(), will implement the copy of the Image Base value and the Offset of Entry Point value into 8 bytes of free space in the loader.

5.1 Restore the first register’s context

It is important to recover the Original Context of the thread. You have not yet done it in the DynLoader Step 2 source code. You can modify the source of DynLoader() to repossess the first Context.

__stdcall void DynLoader(){_asm{//------------------------------------    DWORD_TYPE(DYN_LOADER_START_MAGIC)//------------------------------------Main_0:    PUSHAD// Save the registers context in stack    CALL Main_1Main_1:    POP EBP// Get Base EBP    SUB EBP,OFFSET Main_1    MOV EAX,DWORD PTR [EBP+_RO_dwImageBase]    ADD EAX,DWORD PTR [EBP+_RO_dwOrgEntryPoint]    MOV DWORD PTR [ESP+1Ch],EAX // pStack.Eax <- EAX    POPAD // Restore the first registers context from stack    PUSH EAX    XOR  EAX, EAX    RETN // >> JMP to Original OEP//----------------------------------    DWORD_TYPE(DYN_LOADER_START_DATA1)//----------------------------------_RO_dwImageBase:                DWORD_TYPE(0xCCCCCCCC)_RO_dwOrgEntryPoint:            DWORD_TYPE(0xCCCCCCCC)//----------------------------------    DWORD_TYPE(DYN_LOADER_END_MAGIC)//----------------------------------}}

5.2 Restore the original stack

You also can recover the original stack by setting the value of the beginning stack + 0x34 to the Original OEP, but it is not very important. Nevertheless, in the following code, I have accomplished the loader code by a simple trick to reach the OEP in addition to redecorating the stack. You can observe the implementation by tracing using OllyDbg or SoftICE.

__stdcall void DynLoader(){_asm{//----------------------------------    DWORD_TYPE(DYN_LOADER_START_MAGIC)//----------------------------------Main_0:    PUSHAD    // Save the registers context in stack    CALL Main_1Main_1:    POP EBP    SUB EBP,OFFSET Main_1    MOV EAX,DWORD PTR [EBP+_RO_dwImageBase]    ADD EAX,DWORD PTR [EBP+_RO_dwOrgEntryPoint]    MOV DWORD PTR [ESP+54h],EAX    // pStack.Eip <- EAX    POPAD    // Restore the first registers context from stack    CALL _OEP_Jump    DWORD_TYPE(0xCCCCCCCC)_OEP_Jump:    PUSH EBP    MOV EBP,ESP    MOV EAX,DWORD PTR [ESP+3Ch]    // EAX <- pStack.Eip    MOV DWORD PTR [ESP+4h],EAX     // _OEP_Jump RETURN pointer <- EAX    XOR EAX,EAX    LEAVE    RETN//----------------------------------    DWORD_TYPE(DYN_LOADER_START_DATA1)//----------------------------------_RO_dwImageBase:                DWORD_TYPE(0xCCCCCCCC)_RO_dwOrgEntryPoint:            DWORD_TYPE(0xCCCCCCCC)//----------------------------------    DWORD_TYPE(DYN_LOADER_END_MAGIC)//----------------------------------}}

5.3 Approach OEP by structured exception handling

try-except statement in C++ clarifies the operation of structured exception handling. Besides the assembly code of this code, it elucidates the structured exception handler installation, the raise of an exception, and the exception handler function.

An exception is generated when a program falls into a fault code execution and an error happens, so in such a special condition, the program immediately jumps to a function called the exception handler from exception handler list of the Thread Information Block.

The next example of a

#include "stdafx.h"#include "windows.h"void RAISE_AN_EXCEPTION(){_asm{    INT 3    INT 3    INT 3    INT 3}}int _tmain(int argc, _TCHAR* argv[]){    __try    {        __try{            printf("1: Raise an Exception\n");            RAISE_AN_EXCEPTION();        }        __finally        {            printf("2: In Finally\n");        }    }    __except( printf("3: In Filter\n"), EXCEPTION_EXECUTE_HANDLER )    {        printf("4: In Exception Handler\n");    }    return 0;}

; main()00401000: PUSH EBP00401001: MOV EBP,ESP00401003: PUSH -100401005: PUSH 00407160; __try {; the structured exception handler (SEH) installation 0040100A: PUSH _except_handler30040100F: MOV EAX,DWORD PTR FS:[0]00401015: PUSH EAX00401016: MOV DWORD PTR FS:[0],ESP0040101D: SUB ESP,800401020: PUSH EBX00401021: PUSH ESI00401022: PUSH EDI00401023: MOV DWORD PTR SS:[EBP-18],ESP;     __try {00401026: XOR ESI,ESI00401028: MOV DWORD PTR SS:[EBP-4],ESI0040102B: MOV DWORD PTR SS:[EBP-4],100401032: PUSH OFFSET "1: Raise an Exception"00401037: CALL printf0040103C: ADD ESP,4; the raise a exception, INT 3 exception; RAISE_AN_EXCEPTION()0040103F: INT300401040: INT300401041: INT300401042: INT3;     } __finally {00401043: MOV DWORD PTR SS:[EBP-4],ESI00401046: CALL 0040104D0040104B: JMP 004010800040104D: PUSH OFFSET "2: In Finally"00401052: CALL printf00401057: ADD ESP,40040105A: RETN;     }; }; __except( 0040105B: JMP 004010800040105D: PUSH OFFSET "3: In Filter"00401062: CALL printf00401067: ADD ESP,40040106A: MOV EAX,1 ; EXCEPTION_EXECUTE_HANDLER = 10040106F: RETN;     , EXCEPTION_EXECUTE_HANDLER ); {; the exception handler funtion00401070: MOV ESP,DWORD PTR SS:[EBP-18]00401073: PUSH OFFSET "4: In Exception Handler"00401078: CALL printf0040107D: ADD ESP,4; }00401080: MOV DWORD PTR SS:[EBP-4],-10040108C: XOR EAX,EAX; restore previous SEH0040108E: MOV ECX,DWORD PTR SS:[EBP-10]00401091: MOV DWORD PTR FS:[0],ECX00401098: POP EDI00401099: POP ESI0040109A: POP EBX0040109B: MOV ESP,EBP0040109D: POP EBP0040109E: RETN

Make a Win32 console project, and link and run the preceding C++ code, to perceive the result:

This program runs the exception expression, printf("3: In Filter\n");, when an exception happens—in this example, the INT 3 exception. You can employ other kinds of exception too. In OllyDbg, Debugging options->Exceptions, you can see a short list of different types of exceptions.

5.3.1 Implement Exception Handler

You want to construct a structured exception handler to reach OEP. Now, I think you have distinguished the SEH installation, the exception raise, and the exception expression filter, by foregoing the assembly code. To establish your exception handler approach, you need to comprise the following codes:

• SEH installation:

  LEA EAX,[EBP+_except_handler1_OEP_Jump]PUSH EAXPUSH DWORD PTR FS:[0]MOV DWORD PTR FS:[0],ESP

• An Exception Raise:

  INT 3

• Exception handler expression filter:

  _except_handler1_OEP_Jump:   PUSH EBP   MOV EBP,ESP   ...   // EXCEPTION_CONTINUE_SEARCH = 0   MOV EAX, EXCEPTION_CONTINUE_SEARCH   LEAVE   RETN

So, you yearn to make the ensuing C++ code in assembly language to inaugurate your engine to approach the Offset of the Entry Point by SEH.

__try    // SEH installation{    __asm    {        INT 3    // An Exception Raise    }}__except( ..., EXCEPTION_CONTINUE_SEARCH ){}// Exception handler expression filter

In assembly code…

    ; ----------------------------------------------------    ; the structured exception handler (SEH) installation    ; __try {    LEA EAX,[EBP+_except_handler1_OEP_Jump]    PUSH EAX    PUSH DWORD PTR FS:[0]    MOV DWORD PTR FS:[0],ESP    ; ----------------------------------------------------    ; the raise a INT 3 exception    INT 3    INT 3    INT 3    INT 3    ; }    ; __except( ...     ; ----------------------------------------------------    ; exception handler expression filter_except_handler1_OEP_Jump:    PUSH EBP    MOV EBP,ESP    ...    MOV EAX, EXCEPTION_CONTINUE_SEARCH ; EXCEPTION_CONTINUE_SEARCH = 0    LEAVE    RETN    ; , EXCEPTION_CONTINUE_SEARCH ) { }

The exception value, __except(..., Value), determines how the exception is handled. It can have three values: 1, 0, -1. To understand them, refer to the try-except statement description in the MSDN library. You set it to EXCEPTION_CONTINUE_SEARCH (0), not to run the exception handler function; therefore, by this value, the exception is not recognized. It is simply ignored, and the thread continues its code execution.

How the SEH installation is implemented

As you perceived from the illustrated code, the SEH installation is done by the FS segment register. Microsoft Windows 32 bit uses the FS segment register as a pointer to the data block of the main thread. The first 0x1C bytes comprise the information of the Thread Information Block (TIB). Therefore, FS:[00h] refers to ExceptionList of the main thread, Table 3. In your code, you have pushed the pointer to _except_handler1_OEP_Jump in the stack and changed the value of ExceptionList, FS:[00h], to the beginning of the stack, ESP.

Thread Information Block (TIB)

typedef struct _NT_TIB32 {   DWORD ExceptionList;   DWORD StackBase;   DWORD StackLimit;   DWORD SubSystemTib;   union {      DWORD FiberData;      DWORD Version;   };   DWORD ArbitraryUserPointer;   DWORD Self;} NT_TIB32, *PNT_TIB32;

Table 3: FS segment register and Thread Information Block

5.3.2 Attain OEP by adjusting the Thread Context

In this part, you effectuate your performance by accomplishing the OEP approach. You change the Context of the thread and ignore every simple exception handling, and let the thread continue the execution, but in the original OEP!

When an exception happens, the context of the processor during the time of the exception is saved in the stack. Through

MOV EAX, ContextRecordMOV EDI, dwOEP                   ; EAX <- dwOEPMOV DWORD PTR DS:[EAX+0B8h], EDI ; pContext.Eip <- EAX

#define MAXIMUM_SUPPORTED_EXTENSION     512typedef struct _CONTEXT {    //-----------------------------------------    DWORD ContextFlags;    //-----------------------------------------    DWORD   Dr0;    DWORD   Dr1;    DWORD   Dr2;    DWORD   Dr3;    DWORD   Dr6;    DWORD   Dr7;    //-----------------------------------------    FLOATING_SAVE_AREA FloatSave;    //-----------------------------------------    DWORD   SegGs;    DWORD   SegFs;    DWORD   SegEs;    DWORD   SegDs;    //-----------------------------------------    DWORD   Edi;    DWORD   Esi;    DWORD   Ebx;    DWORD   Edx;    DWORD   Ecx;    DWORD   Eax;    //-----------------------------------------    DWORD   Ebp;    DWORD   Eip;    DWORD   SegCs;    DWORD   EFlags;    DWORD   Esp;    DWORD   SegSs;    //-----------------------------------------    BYTE    ExtendedRegisters[MAXIMUM_SUPPORTED_EXTENSION];    //----------------------------------------} CONTEXT,*LPCONTEXT;

__stdcall void DynLoader(){_asm{//----------------------------------    DWORD_TYPE(DYN_LOADER_START_MAGIC)//----------------------------------Main_0:    PUSHAD  // Save the registers context in stack    CALL Main_1Main_1:    POP EBP    SUB EBP,OFFSET Main_1 // Get Base EBP    MOV EAX,DWORD PTR [EBP+_RO_dwImageBase]    ADD EAX,DWORD PTR [EBP+_RO_dwOrgEntryPoint]    MOV DWORD PTR [ESP+10h],EAX    // pStack.Ebx <- EAX    LEA EAX,[EBP+_except_handler1_OEP_Jump]    MOV DWORD PTR [ESP+1Ch],EAX    // pStack.Eax <- EAX    POPAD  // Restore the first registers context from stack    //----------------------------------------------------    // the structured exception handler (SEH) installation    PUSH EAX    XOR  EAX, EAX    PUSH DWORD PTR FS:[0]       // NT_TIB32.ExceptionList    MOV DWORD PTR FS:[0],ESP    // NT_TIB32.ExceptionList <-ESP    //----------------------------------------------------    // the raise a INT 3 exception    DWORD_TYPE(0xCCCCCCCC)    //--------------------------------------------------------// -------- exception handler expression filter ----------_except_handler1_OEP_Jump:    PUSH EBP    MOV EBP,ESP    //------------------------------    MOV EAX,DWORD PTR SS:[EBP+010h]   // PCONTEXT: pContext <- EAX    //==============================    PUSH EDI    // restore original SEH    MOV EDI,DWORD PTR DS:[EAX+0C4h]    // pContext.Esp    PUSH DWORD PTR DS:[EDI]    POP DWORD PTR FS:[0]    ADD DWORD PTR DS:[EAX+0C4h],8    // pContext.Esp    //------------------------------    // set the Eip to the OEP    MOV EDI,DWORD PTR DS:[EAX+0A4h] // EAX <- pContext.Ebx    MOV DWORD PTR DS:[EAX+0B8h],EDI // pContext.Eip <- EAX    //------------------------------    POP EDI    //==============================    MOV EAX, EXCEPTION_CONTINUE_SEARCH    LEAVE    RETN//----------------------------------    DWORD_TYPE(DYN_LOADER_START_DATA1)//----------------------------------_RO_dwImageBase:                DWORD_TYPE(0xCCCCCCCC)_RO_dwOrgEntryPoint:            DWORD_TYPE(0xCCCCCCCC)//----------------------------------    DWORD_TYPE(DYN_LOADER_END_MAGIC)//----------------------------------}}

There are two ways to use the Windows dynamic link library (DLL) in Windows application programming:

• Using Windows libraries by additional dependencies: 
  

  
  (

  Full Size Image)

• Using Windows dynamic link libraries in run-time:

  // DLL function signaturetypedef HGLOBAL (*importFunction_GlobalAlloc)(UINT, SIZE_T);...importFunction_GlobalAlloc __GlobalAlloc;// Load DLL fileHINSTANCE hinstLib = LoadLibrary("Kernel32.dll");if (hinstLib == NULL){   // Error - unable to load DLL}// Get function pointer__GlobalAlloc =   (importFunction_GlobalAlloc)GetProcAddress(hinstLib,                                              "GlobalAlloc");if (addNumbers == NULL){    // Error - unable to find DLL function}FreeLibrary(hinstLib);

When you make a Windows application project, the linker includes at least kernel32.dll in the base dependencies of your project. Without LoadLibrary() and GetProcAddress() of Kernel32.dll, you cannot load a DLL at run time. The dependencies information is stored in the import table section. By using Dependency Walker, it is not so difficult to observe the DLL module and the functions that are imported into a PE file.

You attempt to establish your custom import table to conduct your project. Furthermore, you have to fix up the original import table at the end to run the real code of the program.

PE Maker: Step 3

Download the pemaker3.zip source files from the end of the article.

6.1 Construct the Client Import Table

I strongly advise that you to read Section 6.4 of the Microsoft Portable Executable and the Common Object File Format Specification document. This section contains the principal information to comprehend the import table performance. The import table data is accessible by a second data directory of the optional header from PE headers, so you can access it by using the following code:

DWORD dwVirtualAddress = image_nt_headers->   OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].      VirtualAddress;DWORD dwSize = image_nt_headers->   OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].      Size;

The VirtualAddress refers to structures by IMAGE_IMPORT_DESCRIPTOR. This structure contains the pointer to the imported DLL name and the relative virtual address of the first thunk.

typedef struct _IMAGE_IMPORT_DESCRIPTOR {    union {        DWORD   Characteristics;        DWORD   OriginalFirstThunk;    };    DWORD   TimeDateStamp;    DWORD   ForwarderChain;    DWORD   Name;         // the imported DLL name    DWORD   FirstThunk;   // the relative virtual address of the                          // first thunk} IMAGE_IMPORT_DESCRIPTOR, *PIMAGE_IMPORT_DESCRIPTOR;

When a program is running, the Windows Task Manager sets the thunks by the virtual address of the function. The virtual address is found by the name of the function. At first, the thunks hold the relative virtual address of the function name, as shown in Table 5; during execution, they are fixed up by the virtual address of the functions (see Table 6).

Table 5: The Import Table in a file image

Table 6: The Import Table in virtual memory

You want to make a simple import table to import LoadLibrary(), and GetProcAddress() from Kernel32.dll. You need these two essential API functions to cover other API functions in run-time. The following assembly code shows how easily you can reach your solution:

0101F000: 00000000 ; OriginalFirstThunk0101F004: 00000000 ; TimeDateStamp0101F008: 00000000 ; ForwarderChain0101F00C: 0001F034 ; Name;       ImageBase + 0001F034                                 -> 0101F034 -> "Kernel32.dll",00101F010: 0001F028 ; FirstThunk; ImageBase + 0001F028 -> 0101F0280101F014: 000000000101F018: 000000000101F01C: 000000000101F020: 000000000101F024: 000000000101F028: 0001F041 ; ImageBase + 0001F041 -> 0101F041                     -> 0,0,"LoadLibraryA",00101F02C: 0001F050 ; ImageBase + 0001F050 -> 0101F050                     -> 0,0,"GetProcAddress",00101F030: 000000000101F034: 'K' 'e' 'r' 'n' 'e' 'l' '3' '2' '.' 'd' 'l' 'l' 0001F041: 00 00 'L' 'o' 'a' 'd' 'L' 'i' 'b' 'r' 'a' 'r' 'y' 'A'0001F050: 00 00 'G' 'e' 't' 'P' 'r' 'o' 'c' 'A' 'd' 'd' 'r' 'e' 's'          's' 00 0000

After running…

0101F000: 00000000 ; OriginalFirstThunk0101F004: 00000000 ; TimeDateStamp0101F008: 00000000 ; ForwarderChain0101F00C: 0001F034 ; Name;       ImageBase + 0001F034                                 -> 0101F034 -> "Kernel32.dll",00101F010: 0001F028 ; FirstThunk; ImageBase + 0001F028 -> 0101F0280101F014: 000000000101F018: 000000000101F01C: 000000000101F020: 000000000101F024: 000000000101F028: 7C801D77 ; -> Kernel32.LoadLibrary()0101F02C: 7C80AC28 ; -> Kernel32.GetProcAddress()0101F030: 000000000101F034: 'K' 'e' 'r' 'n' 'e' 'l' '3' '2' '.' 'd' 'l' 'l' 0001F041: 00 00 'L' 'o' 'a' 'd' 'L' 'i' 'b' 'r' 'a' 'r' 'y' 'A'0001F050: 00 00 'G' 'e' 't' 'P' 'r' 'o' 'c' 'A' 'd' 'd' 'r' 'e' 's'          's' 00 0000

I have prepared a class library to make every import table by using a client string table. The CITMaker class library in itmaker.h; it will build an import table by sz_IT_EXE_strings and also the relative virtual address of the import table.

static const char *sz_IT_EXE_strings[]={    "Kernel32.dll",    "LoadLibraryA",    "GetProcAddress",    0,,    0,};

You subsequently employ this class library to establish an import table to support DLLs and OCXs, so this is a general library to present all possible import tables easily. The next step is clarified in the following code.

CITMaker *ImportTableMaker = new CITMaker( IMPORT_TABLE_EXE );...pimage_section_header=AddNewSection( ".xxx", dwNewSectionSize );// build import table by the current virtual addressImportTableMaker->Build( pimage_section_header->VirtualAddress );memcpy( pNewSection, ImportTableMaker->pMem,ImportTableMaker->dwSize );...memcpy( image_section[image_nt_headers->FileHeader.NumberOfSections-1],        pNewSection,        dwNewSectionSize );...image_nt_headers->OptionalHeader.  DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress  = pimage_section_header->VirtualAddress;image_nt_headers->OptionalHeader.  DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].Size  = ImportTableMaker->dwSize;...delete ImportTableMaker;

The import table is copied at the beginning of the new section, and the relevant data directory is adjusted to the relative virtual address of the new section and the size of the new import table.

6.2 Using other API functions at run time

At this time, you can load other DLLs and find the process address of other functions by using LoadLibrary() and GetProcAddress():

lea edi, @"Kernel32.dll"//-------------------push edimov eax,offset _p_LoadLibrarycall [ebp+eax] //LoadLibrary(lpLibFileName);//-------------------mov esi,eax    // esi -> hModulelea edi, @"GetModuleHandleA"//-------------------push edipush esimov eax,offset _p_GetProcAddresscall [ebp+eax] //GetModuleHandle=GetProcAddress(hModule, lpProcName);//--------------------

 LoadLibrary() and GetProcAddress() aid you in your effort to reach your intention.

I want to have a complete imported function table similar in performance done in a real EXE file. If you look inside a PE file, you will discover that an API call is done by an indirection jump through the virtual address of the API function:

JMP DWORD PTR [XXXXXXXX]

...0101F028: 7C801D77      ; Virtual Address of kernel32.LoadLibrary()...0101F120: JMP DWORD PTR [0101F028]...0101F230: CALL 0101F120 ;  JMP to kernel32.LoadLibrary...

It makes it easy to expand the other part of your project by this performance, so you construct two data tables: the first for API virtual addresses, and the second for the JMP [XXXXXXXX].

#define __jmp_api               byte_type(0xFF) byte_type(0x25)__asm{...//----------------------------------------------------------------_p_GetModuleHandle:             dword_type(0xCCCCCCCC)_p_VirtualProtect:              dword_type(0xCCCCCCCC)_p_GetModuleFileName:           dword_type(0xCCCCCCCC)_p_CreateFile:                  dword_type(0xCCCCCCCC)_p_GlobalAlloc:                 dword_type(0xCCCCCCCC)//----------------------------------------------------------------_jmp_GetModuleHandle:           __jmp_api   dword_type(0xCCCCCCCC)_jmp_VirtualProtect:            __jmp_api   dword_type(0xCCCCCCCC)_jmp_GetModuleFileName:         __jmp_api   dword_type(0xCCCCCCCC)_jmp_CreateFile:                __jmp_api   dword_type(0xCCCCCCCC)_jmp_GlobalAlloc:               __jmp_api   dword_type(0xCCCCCCCC)//----------------------------------------------------------------...}

In the succeeding code, you have concluded your ambition to install a custom internal import table! (You cannot call it import table.)

    ...    lea edi,[ebp+_p_szKernel32]    lea ebx,[ebp+_p_GetModuleHandle]    lea ecx,[ebp+_jmp_GetModuleHandle]    add ecx,02h_api_get_lib_address_loop:        push ecx        push edi        mov eax,offset _p_LoadLibrary        call [ebp+eax]    //LoadLibrary(lpLibFileName);        pop ecx        mov esi,eax       // esi -> hModule        push edi        call __strlen        add esp,04h        add edi,eax_api_get_proc_address_loop:            push ecx            push edi            push esi            mov eax,offset _p_GetProcAddress            //GetModuleHandle=GetProcAddress(hModule, lpProcName);            call [ebp+eax]            pop ecx            mov [ebx],eax            mov [ecx],ebx    // JMP DWORD PTR [XXXXXXXX]            add ebx,04h            add ecx,06h            push edi            call __strlen            add esp,04h            add edi,eax            mov al,byte ptr [edi]        test al,al        jnz _api_get_proc_address_loop        inc edi        mov al,byte ptr [edi]    test al,al    jnz _api_get_lib_address_loop    ...

6.3 Fix up the Original Import Table

To run the program again, you should fix up the thunks of the actual import table; otherwise, you have a corrupted target PE file. Your code must correct all of the thunks the same as Table 5 to Table 6. Once more,

    ...    mov ebx,[ebp+_p_dwImportVirtualAddress]    test ebx,ebx    jz _it_fixup_end    mov esi,[ebp+_p_dwImageBase]    add ebx,esi             // dwImageBase + dwImportVirtualAddress_it_fixup_get_lib_address_loop:        mov eax,[ebx+00Ch]  // image_import_descriptor.Name        test eax,eax        jz _it_fixup_end        mov ecx,[ebx+010h]  // image_import_descriptor.FirstThunk        add ecx,esi        mov [ebp+_p_dwThunk],ecx    // dwThunk        mov ecx,[ebx]       // image_import_descriptor.Characteristics        test ecx,ecx        jnz _it_fixup_table            mov ecx,[ebx+010h]_it_fixup_table:        add ecx,esi        mov [ebp+_p_dwHintName],ecx    // dwHintName        add eax,esi  // image_import_descriptor.Name + dwImageBase = ModuleName        push eax     // lpLibFileName        mov eax,offset _p_LoadLibrary        call [ebp+eax]               // LoadLibrary(lpLibFileName);        test eax,eax        jz _it_fixup_end        mov edi,eax_it_fixup_get_proc_address_loop:            mov ecx,[ebp+_p_dwHintName]    // dwHintName            mov edx,[ecx]            // image_thunk_data.Ordinal            test edx,edx            jz _it_fixup_next_module            test edx,080000000h      // .IF( import by ordinal )            jz _it_fixup_by_name                and edx,07FFFFFFFh    // get ordinal                jmp _it_fixup_get_addr_it_fixup_by_name:            add edx,esi  // image_thunk_data.Ordinal                         // + dwImageBase = OrdinalName            inc edx            inc edx                  // OrdinalName.Name_it_fixup_get_addr:            push edx //lpProcName            push edi                 // hModule            mov eax,offset _p_GetProcAddress            call [ebp+eax]    // GetProcAddress(hModule, lpProcName);            mov ecx,[ebp+_p_dwThunk]    // dwThunk            mov [ecx],eax  // correction the thunk            // dwThunk => next dwThunk            add dword ptr [ebp+_p_dwThunk], 004h            // dwHintName => next dwHintName            add dword ptr [ebp+_p_dwHintName],004h        jmp _it_fixup_get_proc_address_loop_it_fixup_next_module:        add ebx,014h      // sizeof(IMAGE_IMPORT_DESCRIPTOR)    jmp _it_fixup_get_lib_address_loop_it_fixup_end:    ...

7 Support DLL and OCX

Now, you intend to include the dynamic link library (DLL) and OLE-ActiveX Control in your PE builder project. Supporting them is very easy if you pay attention to the two-time arrival into the Offset of Entry Point, the relocation table implementation, and the client import table.
PE Maker: Step 4

 

 LoadLibrary(), or an OCX is registered by using LoadLibrary() and GetProcAddress() through calling DllRegisterServer(), the first of the OEP arrival is done.

 
hinstDLL = LoadLibrary( "test1.dll" );hinstOCX = LoadLibrary( "test1.ocx" );_DllRegisterServer = GetProcAddress( hinstOCX,                                     "DllRegisterServer" );_DllRegisterServer();    // ocx register

Download the pemaker4.zip source files from the end of the article.
7.1 Twice OEP approach
The Offset of Entry Point of a DLL file or an OCX file is touched by the main program atleast twice:

Constructor: When a DLL is loaded by 
Destructor: When the main program frees the library usage by FreeLibrary(), the second OEP arrival happens.
 
FreeLibrary( hinstDLL );FreeLibrary( hinstOCX );


To perform this, I have employed a trick that causes in the second time again, the instruction pointer (EIP) traveling towards the original OEP by the structured exception handler.
_main_0:    pushad    // save the registers context in stack    call _main_1_main_1:    pop ebp    sub ebp,offset _main_1    // get base ebp    //---------------- support dll, ocx  -----------------_support_dll_0:    jmp _support_dll_1        // nop; nop;    // << trick                              // in the second time OEP    jmp _support_dll_2_support_dll_1:    //----------------------------------------------------    ...    //---------------- support dll, ocx  1 ---------------    mov edi,[ebp+_p_dwImageBase]    add edi,[edi+03Ch]            // edi -> IMAGE_NT_HEADERS    mov ax,word ptr [edi+016h]    // edi -> image_nt_headers->                                  // FileHeader.Characteristics    test ax,IMAGE_FILE_DLL    jz _support_dll_2        mov ax, 9090h // << trick        mov word ptr [ebp+_support_dll_0],ax_support_dll_2:    //----------------------------------------------------    ...    into OEP by SEH ...
I hope you caught the trick in the preceding code, but this is not all of it. You have a problem in ImageBase, when the library has been loaded in different image bases by the main program. You should write some code to find the real image base and store it to use forward.
    mov eax,[esp+24h]    // the real imagebase    mov ebx,[esp+30h]    // oep    cmp eax,ebx    ja _no_dll_pe_file_0        cmp word ptr [eax],IMAGE_DOS_SIGNATURE        jne _no_dll_pe_file_0            mov [ebp+_p_dwImageBase],eax_no_dll_pe_file_0:
This code finds the real image base by investigating the stack information. By using the real image base and the formal image base, you should correct all memory calls inside the image program!! Don't be afraid; it will be done simply by the relocating the table information.
7.2 Implement relocation table
To understand the relocation table better, you can take a look at Section 6.6 of the Microsoft Portable Executable and Common Object File Format Specification document. The relocation table contains many packages to relocate the information related to the virtual address inside the virtual memory image. Each package is comprised of an 8-byte header to exhibit the base virtual address and the number of data, demonstrated by the IMAGE_BASE_RELOCATION data structure.
typedef struct _IMAGE_BASE_RELOCATION {   DWORD   VirtualAddress;   DWORD   SizeOfBlock;} IMAGE_BASE_RELOCATION, *PIMAGE_BASE_RELOCATION;
Table 7 - The Relocation Table




Block[1]
VirtualAddress


SizeOfBlock


type:4
offset:12
type:4
offset:12


type:4
offset:12
type:4
offset:12


type:4
offset:12
type:4
offset:12


...
...
...
...


type:4
offset:12
00
00


Block[2]
VirtualAddress


SizeOfBlock


type:4
offset:12
type:4
offset:12


type:4
offset:12
type:4
offset:12


type:4
offset:12
type:4
offset:12


...
...
...
...


type:4
offset:12
00
00


...

 
... 
 



Block[n]
VirtualAddress


SizeOfBlock


type:4
offset:12
type:4
offset:12


type:4
offset:12
type:4
offset:12


type:4
offset:12
type:4
offset:12


...
...
...
...


type:4
offset:12
00
00



Table 7 illustrates the main idea of the relocation table. Furthermore, you can upload a DLL or an OCX file in OllyDbg to observe the relocation table, the ".reloc" section through Memory map window. By the way, you find the position of the relocation table by using the following code in your project:
DWORD dwVirtualAddress = image_nt_headers->  OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_BASERELOC].  VirtualAddress;DWORD dwSize = image_nt_headers->  OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_BASERELOC].Size;
By OllyDbg, you have the same as the following for the ".reloc" section, by using the Long Hex viewer mode. In this example, the base virtual address is 0x1000 and the size of the block is 0x184.
008E1000 : 00001000  00000184  30163000  30403028008E1010 : 30683054  308C3080  30AC309C  30D830CC008E1020 : 30E030DC  30E830E4  30F030EC  310030F4008E1030 : 3120310D  315F3150  31A431A0  31C031A8008E1040 : 31D031CC  31F431EC  31FC31F8  32043200008E1050 : 320C3208  32143210  324C322C  32583254008E1060 : 3260325C  32683264  3270326C  32B03274
It relocates the data in the subsequent virtual addresses:
0x1000 + 0x0000 = 0x10000x1000 + 0x0016 = 0x10160x1000 + 0x0028 = 0x10280x1000 + 0x0040 = 0x10400x1000 + 0x0054 = 0x1054...
Each package performs the relocation by using consecutive 4 bytes form its internal information. The first byte refers to the type of relocation and the next three bytes are the offset that must be used with the base virtual address and the image base to correct the image information.




type
offset


03
00
00
00



What is the type?
The type can be one of the following values:

IMAGE_REL_BASED_ABSOLUTE (0): No effect 
IMAGE_REL_BASED_HIGH (1): Relocate by the high 16 bytes of the base virtual address and the offset 
IMAGE_REL_BASED_LOW (2): Relocate by the low 16 bytes of the base virtual address and the offset 
IMAGE_REL_BASED_HIGHLOW (3): Relocate by the base virtual address and the offset 

What is done in the relocation?
By relocation, some values inside the virtual memory are corrected according to the current image base by the ".reloc" section packages.




delta_ImageBase = current_ImageBase - image_nt_headers->OptionalHeader.ImageBase



mem[ current_ImageBase + 0x1000 ] =   mem[ current_ImageBase + 0x1000 ] + delta_ImageBase ;mem[ current_ImageBase + 0x1016 ] =   mem[ current_ImageBase + 0x1016 ] + delta_ImageBase ;mem[ current_ImageBase + 0x1028 ] =   mem[ current_ImageBase + 0x1028 ] + delta_ImageBase ;mem[ current_ImageBase + 0x1040 ] =   mem[ current_ImageBase + 0x1040 ] + delta_ImageBase ;mem[ current_ImageBase + 0x1054 ] =  mem[ current_ImageBase + 0x1054 ] + delta_ImageBase ;...
I have employed the following code from Morphine packer to implement the relocation.
    ..._reloc_fixup:    mov eax,[ebp+_p_dwImageBase]    mov edx,eax    mov ebx,eax    add ebx,[ebx+3Ch]    // edi -> IMAGE_NT_HEADERS    // edx ->image_nt_headers->OptionalHeader.ImageBase    mov ebx,[ebx+034h]    sub edx,ebx // edx -> reloc_correction    // delta_ImageBase    je _reloc_fixup_end    mov ebx,[ebp+_p_dwRelocationVirtualAddress]    test ebx,ebx    jz _reloc_fixup_end    add ebx,eax_reloc_fixup_block:    mov eax,[ebx+004h]          //ImageBaseRelocation.SizeOfBlock    test eax,eax    jz _reloc_fixup_end    lea ecx,[eax-008h]    shr ecx,001h    lea edi,[ebx+008h]_reloc_fixup_do_entry:        movzx eax,word ptr [edi]//Entry        push edx        mov edx,eax        shr eax,00Ch            //Type = Entry >> 12        mov esi,[ebp+_p_dwImageBase]//ImageBase        and dx,00FFFh        add esi,[ebx]        add esi,edx        pop edx_reloc_fixup_HIGH:              // IMAGE_REL_BASED_HIGH        dec eax        jnz _reloc_fixup_LOW            mov eax,edx            shr eax,010h        //HIWORD(Delta)            jmp _reloc_fixup_LOW_fixup_reloc_fixup_LOW:               // IMAGE_REL_BASED_LOW            dec eax        jnz _reloc_fixup_HIGHLOW        movzx eax,dx            //LOWORD(Delta)_reloc_fixup_LOW_fixup:            add word ptr [esi],ax// mem[x] = mem[x] + delta_ImageBase        jmp _reloc_fixup_next_entry_reloc_fixup_HIGHLOW:           // IMAGE_REL_BASED_HIGHLOW            dec eax        jnz _reloc_fixup_next_entry        add [esi],edx           // mem[x] = mem[x] + delta_ImageBase_reloc_fixup_next_entry:        inc edi        inc edi                 //Entry++        loop _reloc_fixup_do_entry_reloc_fixup_next_base:    add ebx,[ebx+004h]    jmp _reloc_fixup_block_reloc_fixup_end:    ...
7.3 Build a special import table
To support the OLE-ActiveX Control registration, you should present an appropriate import table to your target OCX and DLL file. Therefore, I have established an import table by the following string:
const char *sz_IT_OCX_strings[]={   "Kernel32.dll",   "LoadLibraryA",   "GetProcAddress",   "GetModuleHandleA",   0,   "User32.dll",   "GetKeyboardType",   "WindowFromPoint",   0,   "AdvApi32.dll",   "RegQueryValueExA",   "RegSetValueExA",   "StartServiceA",   0,   "Oleaut32.dll",   "SysFreeString",   "CreateErrorInfo",   "SafeArrayPtrOfIndex",   0,   "Gdi32.dll",   "UnrealizeObject",   0,   "Ole32.dll",   "CreateStreamOnHGlobal",   "IsEqualGUID",   0,   "ComCtl32.dll",   "ImageList_SetIconSize",   0,   0,};
Without these API functions, the library can not be loaded, and moreover the DllregisterServer() and DllUregisterServer() will not operate. In CPECryptor::CryptFile, I have distinguished between EXE files and DLL files in the initialization of the new import table object during creation:
if(( image_nt_headers->FileHeader.Characteristics             & IMAGE_FILE_DLL ) == IMAGE_FILE_DLL ){    ImportTableMaker = new CITMaker( IMPORT_TABLE_OCX );}else{    ImportTableMaker = new CITMaker( IMPORT_TABLE_EXE );}
 
8 Preserve the Thread Local Storage
By using Thread Local Storage (TLS), a program is able to execute a multithreaded process, This performance mostly is used by Borland linkers: Delphi and C++ Builder. When you pack a PE file, you should take care to keep the TLS clean; otherwise, your packer will not support Borland Delphi and C++ Builder linked EXE files. To comprehend TLS, I refer you to Section 6.7 of the Microsoft Portable Executable and Common Object File Format Specification document. You can observe the TLS structure by IMAGE_TLS_DIRECTORY32 in winnt.h.
typedef struct _IMAGE_TLS_DIRECTORY32 {   DWORD   StartAddressOfRawData;   DWORD   EndAddressOfRawData;   DWORD   AddressOfIndex;   DWORD   AddressOfCallBacks;   DWORD   SizeOfZeroFill;   DWORD   Characteristics;} IMAGE_TLS_DIRECTORY32, * PIMAGE_TLS_DIRECTORY32;
     MessageBox() from user32.dll.
To keep the TLS directory safe, I have copied it in a special place inside the loader:
..._tls_dwStartAddressOfRawData:   dword_type(0xCCCCCCCC)_tls_dwEndAddressOfRawData:     dword_type(0xCCCCCCCC)_tls_dwAddressOfIndex:          dword_type(0xCCCCCCCC)_tls_dwAddressOfCallBacks:      dword_type(0xCCCCCCCC)_tls_dwSizeOfZeroFill:          dword_type(0xCCCCCCCC)_tls_dwCharacteristics:         dword_type(0xCCCCCCCC)...
It is necessary to correct the TLS directory entry in the Optional Header:
if(image_nt_headers->   OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_TLS].   VirtualAddress!=0){   memcpy(&pDataTable->image_tls_directory,          image_tls_directory,          sizeof(IMAGE_TLS_DIRECTORY32));   dwOffset=DWORD(pData1)-DWORD(pNewSection);   dwOffset+=sizeof(t_DATA_1)-sizeof(IMAGE_TLS_DIRECTORY32);   image_nt_headers->      OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_TLS].      VirtualAddress=dwVirtualAddress + dwOffset;}
9 Inject Your Code
You are ready to place your code inside the new section. Your code is a "Hello World!" message by 
...push MB_OK | MB_ICONINFORMATIONlea eax,[ebp+_p_szCaption]push eaxlea eax,[ebp+_p_szText]push eaxpush NULLcall _jmp_MessageBox// MessageBox(NULL, szText, szCaption, MB_OK | MB_ICONINFORMATION) ;...
PE Maker: Step 5
Download the pemaker5.zip source files from the end of the article.

10 Conclusion
By reading this article, you have perceived how easily you can inject code to a portable executable file. You can complete the code by using the source of other packers, create a packer in the same way as Yoda's Protector, and make your packer undetectable by mixing up with Morphine source code. I hope that you have enjoyed this brief discussion of one part of the reverse engineering field. See you again in the next discussion!
 

EXCEPTION_POINTERS, you have access to the pointer of ContextRecord. The ContextRecord has the CONTEXT data structure, as seen in Table 4. This is the thread context during the exception time. When you ignore the exception by EXCEPTION_CONTINUE_SEARCH (0), the instruction pointer, as well as the context, will be set to ContextRecord to return to the previous condition. Therefore, if you change the Eip of the Win32 Thread Context to the Original Offset of Entry Point, it will come clearly into OEP.Full Size Image)