Inject Your Code to a Portable Executable File[www.codeguru.com]
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| Ashkbiz Danehkar (view profile) March 2, 2006 |
Environment: VC++ .NET 8.0, Windows (Win9x, WinME, NT4, Win2K, WinXP, Win2003, Vista)
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
This sample is useful for the whole of this article.
Table 1: Portable Executable file format structure
| MS-DOS information |
IMAGE_DOS_ HEADER |
DOS EXE Signature | 00000000 ASCII "MZ" 00000002 DW 0090 00000004 DW 0003 00000006 DW 0000 00000008 DW 0004 0000000A DW 0000 0000000C DW FFFF 0000000E DW 0000 00000010 DW 00B8 00000012 DW 0000 00000014 DW 0000 00000016 DW 0000 00000018 DW 0040 0000001A DW 0000 0000001C DB 00 b& b& 0000003B DB 00 0000003C DD 000000F0 |
| DOS_PartPag | |||
| DOS_PageCnt | |||
| DOS_ReloCnt | |||
| DOS_HdrSize | |||
| DOS_MinMem | |||
| DOS_MaxMem | |||
| DOS_ReloSS | |||
| DOS_ExeSP | |||
| DOS_ChkSum | |||
| DOS_ExeIPP | |||
| DOS_ReloCS | |||
| DOS_TablOff | |||
| DOS_Overlay | |||
| b& Reserved words b& |
|||
| Offset to PE signature | |||
| MS-DOS Stub Program |
00000040 ..B:..B4.C !B8/LC !This program canno 00000060 t be run in DOS mode. ...$....... |
||
| Windows NT information IMAGE_ |
Signature | PE signature (PE) | 000000F0 ASCII "PE" |
| IMAGE_ FILE_HEADER |
Machine | 000000F4 DW 014C 000000F6 DW 0003 000000F8 DD 3B7D8410 000000FC DD 00000000 00000100 DD 00000000 00000104 DW 00E0 00000106 DW 010F |
|
| NumberOfSections | |||
| TimeDateStamp | |||
| PointerToSymbolTable | |||
| NumberOfSymbols | |||
| SizeOfOptionalHeader | |||
| Characteristics | |||
| IMAGE_ OPTIONAL_ HEADER32 |
MagicNumber | 00000108 DW 010B 0000010A DB 07 0000010B DB 00 0000010C DD 00012800 00000110 DD 00009C00 00000114 DD 00000000 00000118 DD 00012475 0000011C DD 00001000 00000120 DD 00014000 00000124 DD 01000000 00000128 DD 00001000 0000012C DD 00000200 00000130 DW 0005 00000132 DW 0001 00000134 DW 0005 00000136 DW 0001 00000138 DW 0004 0000013A DW 0000 0000013C DD 00000000 00000140 DD 0001F000 00000144 DD 00000400 00000148 DD 0001D7FC 0000014C DW 0002 0000014E DW 8000 00000150 DD 00040000 00000154 DD 00001000 00000158 DD 00100000 0000015C DD 00001000 00000160 DD 00000000 00000164 DD 00000010 |
|
| MajorLinkerVersion | |||
| MinorLinkerVersion | |||
| SizeOfCode | |||
| SizeOfInitializedData | |||
| SizeOfUninitializedData | |||
| AddressOfEntryPoint | |||
| BaseOfCode | |||
| BaseOfData | |||
| ImageBase | |||
| SectionAlignment | |||
| FileAlignment | |||
| MajorOSVersion | |||
| MinorOSVersion | |||
| MajorImageVersion | |||
| MinorImageVersion | |||
| MajorSubsystemVersion | |||
| MinorSubsystemVersion | |||
| Reserved | |||
| SizeOfImage | |||
| SizeOfHeaders | |||
| CheckSum | |||
| Subsystem | |||
| DLLCharacteristics | |||
| SizeOfStackReserve | |||
| SizeOfStackCommit | |||
| SizeOfHeapReserve | |||
| SizeOfHeapCommit | |||
| LoaderFlags | |||
| NumberOfRvaAndSizes | |||
| IMAGE_ DATA_DIRECTORY[16] |
Export Table | ||
| Import Table | |||
| Resource Table | |||
| Exception Table | |||
| Certificate File | |||
| Relocation Table | |||
| Debug Data | |||
| Architecture Data | |||
| Global Ptr | |||
| TLS Table | |||
| Load Config Table | |||
| Bound Import Table | |||
| Import Address Table | |||
| Delay Import Descriptor | |||
| COM+ Runtime Header | |||
| Reserved | |||
| Sections information |
IMAGE_ SECTION_ HEADER[0] |
Name[8] | 000001E8 ASCII".text"
000001F0 DD 000126B0
000001F4 DD 00001000
000001F8 DD 00012800
000001FC DD 00000400
00000200 DD 00000000
00000204 DD 00000000
00000208 DW 0000
0000020A DW 0000
0000020C DD 60000020
CODE|EXECUTE|READ |
| VirtualSize | |||
| VirtualAddress | |||
| SizeOfRawData | |||
| PointerToRawData | |||
| PointerToRelocations | |||
| PointerToLineNumbers | |||
| NumberOfRelocations | |||
| NumberOfLineNumbers | |||
| Characteristics | |||
| b& b& b& IMAGE_ SECTION_ HEADER[n] |
00000210 ASCII".data"; SECTION
00000218 DD 0000101C ; VirtualSize = 0x101C
0000021C DD 00014000 ; VirtualAddress = 0x14000
00000220 DD 00000A00 ; SizeOfRawData = 0xA00
00000224 DD 00012C00 ; PointerToRawData = 0x12C00
00000228 DD 00000000 ; PointerToRelocations = 0x0
0000022C DD 00000000 ; PointerToLineNumbers = 0x0
00000230 DW 0000 ; NumberOfRelocations = 0x0
00000232 DW 0000 ; NumberOfLineNumbers = 0x0
00000234 DD C0000040 ; Characteristics =
INITIALIZED_DATA|READ|WRITE
00000238 ASCII".rsrc"; SECTION
00000240 DD 00008960 ; VirtualSize = 0x8960
00000244 DD 00016000 ; VirtualAddress = 0x16000
00000248 DD 00008A00 ; SizeOfRawData = 0x8A00
0000024C DD 00013600 ; PointerToRawData = 0x13600
00000250 DD 00000000 ; PointerToRelocations = 0x0
00000254 DD 00000000 ; PointerToLineNumbers = 0x0
00000258 DW 0000 ; NumberOfRelocations = 0x0
0000025A DW 0000 ; NumberOfLineNumbers = 0x0
0000025C DD 40000040 ; Characteristics =
INITIALIZED_DATA|READ
|
||
| SECTION[0] | 00000400 EA 22 DD 77 D7 23 DD 77 C*"C.wC.#C.w 00000408 9A 18 DD 77 00 00 00 00 E!.C.w.... 00000410 2E 1E C7 77 83 1D C7 77 ..C.wF..C.w 00000418 FF 1E C7 77 00 00 00 00 C?.C.w.... 00000420 93 9F E7 77 D8 05 E8 77 b.E8C'wC..C(w 00000428 FD A5 E7 77 AD A9 E9 77 C=B%C'w­B)C)w 00000430 A3 36 E7 77 03 38 E7 77 B#6C'w.8C'w 00000438 41 E3 E6 77 60 8D E7 77 AC#C&w`B C'w 00000440 E6 1B E6 77 2B 2A E7 77 C&.C&w+*C'w 00000448 7A 17 E6 77 79 C8 E6 77 z.C&wyC.C&w 00000450 14 1B E7 77 C1 30 E7 77 ..C'wC.0C'w b& |
||
| b& b& b& SECTION[n] |
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->NumberOfSections
OptionalHeader->AddressOfEntryPoint
OptionalHeader->ImageBase
OptionalHeader->SectionAlignment
OptionalHeader->FileAlignment
OptionalHeader->SizeOfImage
OptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]
->VirtualAddress
OptionalHeader->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
| ".text" | Code Section |
| "CODE" | Code Section of file linked by Borland Delphi or Borland Pascal |
| ".data" | Data Section |
| "DATA" | Data Section of file linked by Borland Delphi or Borland Pascal |
| ".rdata" | Section for Constant Data |
| ".idata" | Import Table |
| ".edata" | Export Table |
| ".tls" | TLS Table |
| ".reloc" | Relocation Information |
| ".rsrc" | Resource Information |
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
| EAX=00000000EBX=7FFDD000 ECX=0007FFB0 EDX=7C90EB94 ESI=FFFFFFFF EDI=7C919738 EBP=0007FFF0 ESP=0007FFC4 EIP=010119E0 o d i s z a p c CS=0008 DS=0023 SS=0010 ES=0023 FS=0030 GS=0000 SS:0007FFC4=87C816D4F |
| 0023:01013000 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................ 0023:01013010 01 00 00 00 20 00 00 00-0A 00 00 00 0A 00 00 00 ................ 0023:01013020 20 00 00 00 00 00 00 00-53 63 69 43 61 6C 63 00 ........SciCalc. 0023:01013030 00 00 00 00 00 00 00 00-62 61 63 6B 67 72 6F 75 ........backgrou 0023:01013040 6E 64 00 00 00 00 00 00-2E 00 00 00 00 00 00 00 nd.............. |
| 0010:0007FFC4 4F 6D 81 7C 38 07 91 7C-FF FF FF FF 00 90 FD 7F Om |8 b.| . 0010:0007FFD4 ED A6 54 80 C8 FF 07 00-E8 B4 F5 81 FF FF FF FF T . 0010:0007FFE4 F3 99 83 7C 58 6D 81 7C-00 00 00 00 00 00 00 00 Xm |........ 0010:0007FFF4 00 00 00 00 E0 19 01 01-00 00 00 00 00 00 00 00 .... .... |
| 010119E0 PUSH EBP 010119E1 MOV EBP,ESP 010119E3 PUSH -1 010119E5 PUSH 01001570 010119EA PUSH 01011D60 010119EF MOV EAX,DWORD PTR FS:[0] 010119F5 PUSH EAX 010119F6 MOV DWORD PTR FS:[0],ESP 010119FD ADD ESP,-68 01011A00 PUSH EBX 01011A01 PUSH ESI 01011A02 PUSH EDI 01011A03 MOV DWORD PTR SS:[EBP-18],ESP 01011A06 MOV DWORD PTR SS:[EBP-4],0 |
| :_ |
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
(Full Size Image)
3.1.3 Which parts are important in a debugger interface?
I have introduced two debuggers without talking about how you can employ them, and also which parts you should pay attention to. Regarding using debuggers, I refer you to their instructions in help documents. However, I want to explain briefly the important parts of a debugger; of course, I am talking about low-level debuggers, or in other words, machine-language debuggers of the x86 CPU families.
All of low-level debuggers consist of the following subdivisions:
- Registers viewer.
EAX ECX EDX EBX ESP EBP ESI EDI EIP o d t s z a p c
- Disassembler or Code viewer.
010119E0 PUSH EBP 010119E1 MOV EBP,ESP 010119E3 PUSH -1 010119E5 PUSH 01001570 010119EA PUSH 01011D60 010119EF MOV EAX,DWORD PTR FS:[0] 010119F5 PUSH EAX 010119F6 MOV DWORD PTR FS:[0],ESP 010119FD ADD ESP,-68 01011A00 PUSH EBX 01011A01 PUSH ESI 01011A02 PUSH EDI 01011A03 MOV DWORD PTR SS:[EBP-18],ESP 01011A06 MOV DWORD PTR SS:[EBP-4],0
- Memory watcher.
0023:01013000 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................ 0023:01013010 01 00 00 00 20 00 00 00-0A 00 00 00 0A 00 00 00 ................ 0023:01013020 20 00 00 00 00 00 00 00-53 63 69 43 61 6C 63 00 ........SciCalc. 0023:01013030 00 00 00 00 00 00 00 00-62 61 63 6B 67 72 6F 75 ........backgrou 0023:01013040 6E 64 00 00 00 00 00 00-2E 00 00 00 00 00 00 00 nd.............. - Stack viewer.
0010:0007FFC4 4F 6D 81 7C 38 07 91 7C-FF FF FF FF 00 90 FD 7F Om |8 b.| . 0010:0007FFD4 ED A6 54 80 C8 FF 07 00-E8 B4 F5 81 FF FF FF FF T . 0010:0007FFE4 F3 99 83 7C 58 6D 81 7C-00 00 00 00 00 00 00 00 Xm |........ 0010:0007FFF4 00 00 00 00 E0 19 01 01-00 00 00 00 00 00 00 00 .... .... - Command line, command buttons, or shortcut keys to follow the debugging process.
Command SoftICE OllyDbg Run F5 F9 Step Into F11 F7 Step Over F10 F8 Set Break Point F8 F2
You can compare Figures 1 and 2 to distinguish the difference between SoftICE and OllyDbg. When you want to trace a PE file, you should mostly consider these five subdivisions. Furthermore, every debugger comprises of some other useful parts; you should discover them by yourself.
3.2 Disassembler
You can consider OllyDbg and SoftICE to be excellent disassemblers, but I also want to introduce another disassembler tool that is famous in the reverse engineering world.
3.2.1 Proview disassembler
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
00000000 00000002 00000004 00000006 00000008 0000000A 0000000C 0000000E 00000010 00000012 00000014 00000016 00000018 0000001A 0000001C 0000001D 0000001E 0000001F 00000020 00000021 00000022 00000023 00000024 00000025 00000026 00000027 00000028 00000029 0000002A 0000002B 0000002C 0000002D 0000002E 0000002F 00000030 00000031 00000032 00000033 00000034 00000035 00000036 00000037 00000038 00000039 0000003A 0000003B 0000003C |
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 |
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 df hjg: inc eax df: 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_1 Main_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_1 Main_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_1 Main_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
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 EBP 00401001: MOV EBP,ESP 00401003: PUSH -1 00401005: PUSH 00407160 ; __try { ; the structured exception handler (SEH) installation 0040100A: PUSH _except_handler3 0040100F: MOV EAX,DWORD PTR FS:[0] 00401015: PUSH EAX 00401016: MOV DWORD PTR FS:[0],ESP 0040101D: SUB ESP,8 00401020: PUSH EBX 00401021: PUSH ESI 00401022: PUSH EDI 00401023: MOV DWORD PTR SS:[EBP-18],ESP ; __try { 00401026: XOR ESI,ESI 00401028: MOV DWORD PTR SS:[EBP-4],ESI 0040102B: MOV DWORD PTR SS:[EBP-4],1 00401032: PUSH OFFSET "1: Raise an Exception" 00401037: CALL printf 0040103C: ADD ESP,4 ; the raise a exception, INT 3 exception ; RAISE_AN_EXCEPTION() 0040103F: INT3 00401040: INT3 00401041: INT3 00401042: INT3 ; } __finally { 00401043: MOV DWORD PTR SS:[EBP-4],ESI 00401046: CALL 0040104D 0040104B: JMP 00401080 0040104D: PUSH OFFSET "2: In Finally" 00401052: CALL printf 00401057: ADD ESP,4 0040105A: RETN ; } ; } ; __except( 0040105B: JMP 00401080 0040105D: PUSH OFFSET "3: In Filter" 00401062: CALL printf 00401067: ADD ESP,4 0040106A: MOV EAX,1 ; EXCEPTION_EXECUTE_HANDLER = 1 0040106F: RETN ; , EXCEPTION_EXECUTE_HANDLER ) ; { ; the exception handler funtion 00401070: MOV ESP,DWORD PTR SS:[EBP-18] 00401073: PUSH OFFSET "4: In Exception Handler" 00401078: CALL printf 0040107D: ADD ESP,4 ; } 00401080: MOV DWORD PTR SS:[EBP-4],-1 0040108C: XOR EAX,EAX ; restore previous SEH 0040108E: MOV ECX,DWORD PTR SS:[EBP-10] 00401091: MOV DWORD PTR FS:[0],ECX 00401098: POP EDI 00401099: POP ESI 0040109A: POP EBX 0040109B: MOV ESP,EBP 0040109D: POP EBP 0040109E: RETNMake a Win32 console project, and link and run the preceding C++ code, to perceive the result:
| 1: Raise an Exception 3: In Filter 2: In Finally 4: In Exception Handler _ |
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 EAX PUSH 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
| DWORD PTR FS:[00h] | ExceptionList |
| DWORD PTR FS:[04h] | StackBase |
| DWORD PTR FS:[08h] | StackLimit |
| DWORD PTR FS:[0Ch] | SubSystemTib |
| DWORD PTR FS:[10h] | FiberData / Version |
| DWORD PTR FS:[14h] | ArbitraryUserPointer |
| DWORD PTR FS:[18h] | Self |
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, ContextRecord MOV EDI, dwOEP ; EAX <- dwOEP MOV DWORD PTR DS:[EAX+0B8h], EDI ; pContext.Eip <- EAX
Win32 Thread Context structure
#define MAXIMUM_SUPPORTED_EXTENSION 512 typedef 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;
Table 4: CONTEXT
| Context Flags | 0x00000000 | ContextFlags | |
| Context Debug Registers |
0x00000004 | Dr0 | |
| 0x00000008 | Dr1 | ||
| 0x0000000C | Dr2 | ||
| 0x00000010 | Dr3 | ||
| 0x00000014 | Dr6 | ||
| 0x00000018 | Dr7 | ||
| Context Floating Point |
0x0000001C | FloatSave | StatusWord |
| 0x00000020 | StatusWord | ||
| 0x00000024 | TagWord | ||
| 0x00000028 | ErrorOffset | ||
| 0x0000002C | ErrorSelector | ||
| 0x00000030 | DataOffset | ||
| 0x00000034 | DataSelector | ||
| 0x00000038 ... 0x00000087 |
RegisterArea [0x50] | ||
| 0x00000088 | Cr0NpxState | ||
| Context Segments | 0x0000008C | SegGs | |
| 0x00000090 | SegFs | ||
| 0x00000094 | SegEs | ||
| 0x00000098 | SegDs | ||
| Context Integer | 0x0000009C | Edi | |
| 0x000000A0 | Esi | ||
| 0x000000A4 | Ebx | ||
| 0x000000A8 | Edx | ||
| 0x000000AC | Ecx | ||
| 0x000000B0 | Eax | ||
| Context Control | 0x000000B4 | Ebp | |
| 0x000000B8 | Eip | ||
| 0x000000BC | SegCs | ||
| 0x000000C0 | EFlags | ||
| 0x000000C4 | Esp | ||
| 0x000000C8 | SegSs | ||
| Context Extended Registers | 0x000000CC |
ExtendedRegisters[0x200] | |
By the following code, you have accomplished the main purpose of coming to OEP by the structured exception handler:
__stdcall void DynLoader() { _asm { //---------------------------------- DWORD_TYPE(DYN_LOADER_START_MAGIC) //---------------------------------- Main_0: PUSHAD // Save the registers context in stack CALL Main_1 Main_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) //---------------------------------- } }
6 Build an Import Table and Reconstruct the Original Import Table
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 signature typedef HGLOBAL (*importFunction_GlobalAlloc)(UINT, SIZE_T); ... importFunction_GlobalAlloc __GlobalAlloc; // Load DLL file HINSTANCE 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
IMAGE_IMPORT_
DESCRIPTOR[0]OriginalFirstThunk TimeDateStamp ForwarderChain Name_RVA ------> "kernel32.dll",0 FirstThunk_RVA ------> proc_1_name_RVA ------> 0,0,"LoadLibraryA",0 proc_2_name_RVA ------> 0,0,"GetProcAddress",0 proc_3_name_RVA ------> 0,0,"GetModuleHandleA",0 ... IMAGE_IMPORT_
DESCRIPTOR[1]... IMAGE_IMPORT_
DESCRIPTOR[n]Table 6: The Import Table in virtual memory
IMAGE_IMPORT_DESCRIPTOR[0] OriginalFirstThunk TimeDateStamp ForwarderChain Name_RVA ------> "kernel32.dll",0 FirstThunk_RVA ------> proc_1_VA proc_2_VA proc_3_VA ... IMAGE_IMPORT_DESCRIPTOR[1] ... IMAGE_IMPORT_DESCRIPTOR[n] 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 ; OriginalFirstThunk 0101F004: 00000000 ; TimeDateStamp 0101F008: 00000000 ; ForwarderChain 0101F00C: 0001F034 ; Name; ImageBase + 0001F034 -> 0101F034 -> "Kernel32.dll",0 0101F010: 0001F028 ; FirstThunk; ImageBase + 0001F028 -> 0101F028 0101F014: 00000000 0101F018: 00000000 0101F01C: 00000000 0101F020: 00000000 0101F024: 00000000 0101F028: 0001F041 ; ImageBase + 0001F041 -> 0101F041 -> 0,0,"LoadLibraryA",0 0101F02C: 0001F050 ; ImageBase + 0001F050 -> 0101F050 -> 0,0,"GetProcAddress",0 0101F030: 00000000 0101F034: '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 0000After running...
0101F000: 00000000 ; OriginalFirstThunk 0101F004: 00000000 ; TimeDateStamp 0101F008: 00000000 ; ForwarderChain 0101F00C: 0001F034 ; Name; ImageBase + 0001F034 -> 0101F034 -> "Kernel32.dll",0 0101F010: 0001F028 ; FirstThunk; ImageBase + 0001F028 -> 0101F028 0101F014: 00000000 0101F018: 00000000 0101F01C: 00000000 0101F020: 00000000 0101F024: 00000000 0101F028: 7C801D77 ; -> Kernel32.LoadLibrary() 0101F02C: 7C80AC28 ; -> Kernel32.GetProcAddress() 0101F030: 00000000 0101F034: '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 0000I 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 address ImportTableMaker->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 edi mov eax,offset _p_LoadLibrary call [ebp+eax] //LoadLibrary(lpLibFileName); //------------------- mov esi,eax // esi -> hModule lea edi, @"GetModuleHandleA" //------------------- push edi push esi mov eax,offset _p_GetProcAddress call [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 30403028 008E1010 : 30683054 308C3080 30AC309C 30D830CC 008E1020 : 30E030DC 30E830E4 30F030EC 310030F4 008E1030 : 3120310D 315F3150 31A431A0 31C031A8 008E1040 : 31D031CC 31F431EC 31FC31F8 32043200 008E1050 : 320C3208 32143210 324C322C 32583254 008E1060 : 3260325C 32683264 3270326C 32B03274
It relocates the data in the subsequent virtual addresses:
0x1000 + 0x0000 = 0x1000 0x1000 + 0x0016 = 0x1016 0x1000 + 0x0028 = 0x1028 0x1000 + 0x0040 = 0x1040 0x1000 + 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;
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. 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.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_ICONINFORMATION lea eax,[ebp+_p_szCaption] push eax lea eax,[ebp+_p_szText] push eax push NULL call _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!
MessageBox() from user32.dll.
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.
| Virtual_Address = Image_Base + Relative_Virtual_Address |
DWORD OEP_RVA = image_nt_headers-> OptionalHeader.AddressOfEntryPoint ; // OEP_RVA = 0x00012475 DWORD OEP_VA = image_nt_headers-> OptionalHeader.ImageBase + OEP_RVA ; // OEP_VA = 0x01000000 + 0x00012475 = 0x01012475
PE Maker: Step 1
Download pemaker1.zip and test1.zip from the files at the end of this article.
DynLoader(), in loader.cpp, is reserved for the data of the new section—in other words, the Loader.
DynLoader Step 1
__stdcall void DynLoader() { _asm { //---------------------------------- DWORD_TYPE(DYN_LOADER_START_MAGIC) //---------------------------------- MOV EAX,01012475h // << Original OEP JMP EAX //---------------------------------- DWORD_TYPE(DYN_LOADER_END_MAGIC) //---------------------------------- } }
Unfortunately, this source can only be applied for the sample test file. You should complete it by saving the value of the original OEP in the new section, and use it to reach the real OEP. I have accomplished it in Step 2 (Section 5).
4.1 Retrieve and Rebuild PE file
I have made a simple class library to recover PE information and to use it in a new PE file.
CPELibrary Class Step 1
//---------------------------------------------------------------- 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); //----------------------------------------- };
In Table 1, the usage of image_dos_header, pDosStub, image_nt_headers, image_section_header [MAX_SECTION_NUM], and image_section[MAX_SECTION_NUM] is clear. You use OpenFile() and SaveFile() to retrieve and rebuild a PE file. Furthermore, AddNewSection() is employed to create the new section, the important step.