[PE Format] Getting offset insaid a file

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marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

How can I get offset inside a file ?

Code:

format pe gui 4.0
entry  start
include  'win32ax.inc'
section 'data' data readable writeable
        buffer        TCHAR    20   dup 0

section 'code' code readable executable
start:
             cinvoke          wsprintf, buffer, '%x', start
             invoke            MessageBox, 0, buffer, NULL, MB_OK
             invoke           ExitProcess, 0

In this way i getting absolutely address in memory but i need to get offset of start label in file.
Sorry for my English.

22 Nov 2011, 21:36

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler

Your loaded exe or some other?

23 Nov 2011, 00:07

typedef

Joined: 25 Jul 2010
Posts: 2908
Location: 0x77760000

typedef

Code:

mov eax,[400000h]

eax = IMAGE_DOS_HEADER

or  GetModuleHandle(0) == 
      'PE'
      IMAGE_FILE_HEADER

Traverse through that and find the entry point/start address of your code

Last edited by typedef on 23 Nov 2011, 13:28; edited 1 time in total

23 Nov 2011, 10:13

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

@mindcooler yes im loaded exe.

@typedef it is value of e_ip field im right ?

23 Nov 2011, 10:56

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler

e_lfanew=60 is the ofset to the PE image. BaseOfCode is 44 bytes into PE structure, inside the optional header.

23 Nov 2011, 11:15

DOS386

Joined: 08 Dec 2006
Posts: 1898

DOS386

Quote:

In this way i getting absolutely address in memory but i need to get offset of start label in file.

You must look at both the section table and the directories to localize stuff inside PE. And you must carefully check every single value for validity: is the address inside any section ? is the section completely inside the file ?

23 Nov 2011, 13:54

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

So what i do wrong in this code :

Code:

format pe gui 4.0
entry  start
include 'win32ax.inc'
section   '.idata' import data readable
library kernel32,'kernel32',user32,'user32'
include 'api\kernel32.inc'
include 'api\user32.inc'
section '.data' data readable writeable

        textbuffer              TCHAR   30 dup 0

section '.text' code readable executable

start:
        mov        ebx, 400000h                         ; EBX = IMAGE_DOS_HEADER
        add        ebx, IMAGE_DOS_HEADER.e_lfanew       ; [EBX] = is the offset to the PE image
                                                        ; in this case = 80h

        mov        eax, [ebx]
        add        eax, 400000h                         ; EAX = IMAGE_NT_HEADERS32
        add        eax, IMAGE_NT_HEADERS32.OptionalHeader; EAX = IMAGE_OPTIONAL_HEADER32
        add        eax, IMAGE_OPTIONAL_HEADER32.AddressOfEntryPoint ; EAX = RVA (EntryPoint) = 3000h in this case
        add        eax, 400000h                         ; EAX = VA (EntryPoint)

        cinvoke    wsprintf, textbuffer, '%x', dword [eax]  ; NOW IS CRASH
        stdcall    msg, textbuffer
        invoke     ExitProcess, 0



proc msg stdcall, message
     invoke       MessageBox, 0, [message], '#PROGRAM INFO',0
     ret
endp

03 Dec 2011, 23:14

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler

You're adding $400000 twice to address of entrypoint address.

Code:

        mov        ebx, 400000h                         ; EBX = IMAGE_DOS_HEADER 
        add        ebx, 60      ; [EBX] = is the offset to the PE image
                                                        ; in this case = 80h 

        mov        eax, [ebx] 
        add        eax, 400000h                         ; EAX = IMAGE_NT_HEADERS32 
        add        eax, 44
        mov        eax,[eax]
        add        eax, 400000h                         ; EAX = VA (EntryPoint)

        cinvoke    wsprintf, textbuffer, '%x', eax  ; NOW IS CRASH

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Last edited by mindcooler on 23 Dec 2011, 01:11; edited 1 time in total

04 Dec 2011, 03:24

typedef

Joined: 25 Jul 2010
Posts: 2908
Location: 0x77760000

typedef

here's a self hexing C code I wrote a while ago maybe you can look and pick something up from it

Code:




#define BASE  0x400000 // base address of image
#define ENTRY 0x4000A8 // offset to entry point (BASE + (int*)(0x400000))
#define PEHDR 0x400080 // address of pe header
#define SIZE  0x40009C // size of code
#define CBASE 0x4000AC // BaseOfCode

#include <stdio.h>

#define CODEBASE(base) \
__asm     mov     eax,    [CBASE] \
__asm     add     eax,    BASE \
__asm        mov base,       eax

#define ENTRYPOINT(pointer) \
__asm      mov     eax,     [ENTRY] \
__asm    add eax,         BASE   \
__asm     mov pointer, eax                \


#define CODESIZE(size) \
__asm        mov eax,        [SIZE] \
__asm      mov size,       eax

int main(int argc, char *argv[])
{

   int size;

       char  * temp;

   char * dump;

    int EntryPoint;
     
    ENTRYPOINT(EntryPoint);

 CODESIZE(size);

 CODEBASE(dump);

     printf("size: %i\n",size);
               printf("Entry: 0x%P\n\n\nDumping code from Base of code: 0x400100\n\n",EntryPoint);

              for(int i =0; i < size; i++)
             {
              printf("%P: ",dump);

              temp = dump;

            for(int x = 0; x < 16; x++)
              {
                      printf("%02X ",(unsigned char)temp[x]);
           }

          printf("\n");
            dump+=16;
           getchar();
          }

  
   return 0;
}

04 Dec 2011, 04:14

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

Ok, thanks i can understand it. I have just one more question:
How VA address converted to RAW ? On this same example
We have VA (EntryPoint):

Code:

section '.text' code readable executable

start:

        mov        ebx, 400000h                         ; EBX = IMAGE_DOS_HEADER
        add        ebx, IMAGE_DOS_HEADER.e_lfanew       ; [EBX] = is the offset to the PE image                                                        ; in this case = 80h
        mov        eax, [ebx]
        add        eax, 400000h                         ; EAX = VA (IMAGE_NT_HEADERS32)


        add        eax, 44
        mov        eax, [eax]
        add        eax, 400000h                         ; EAX = VA (EntryPoint)

        cinvoke    wsprintf, textbuffer, '%x', eax
        stdcall    msg, textbuffer
        invoke     ExitProcess, 0

I know that it is described on MSDN but my english is terrible ... most easy to understand for me is on the example

Last edited by marcinzabrze12 on 05 Dec 2011, 04:05; edited 1 time in total

04 Dec 2011, 19:28

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz

VA = RVA + ImageBase
RVA = VA - ImageBase
...

04 Dec 2011, 20:22

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

sorry i think about RAW not RVA

05 Dec 2011, 04:04

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz

Try this:
http://www.woodmann.com/forum/archive/index.php/t-1798.html

05 Dec 2011, 07:30

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

thanks overflowz i have everything now.

05 Dec 2011, 17:59

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