Write code that can be runs in any memory address?

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ivan_tux

Joined: 23 Jun 2012
Posts: 27
Location: Indonesia

ivan_tux 14 Jun 2016, 11:36

Hi all..
I've been wrote a executable injector and the tested injected code can running perfectly by now.
I place code and data in one section. These part will be loaded to memory, depends on the exe configuration, so the code must can be run in any addresses of memory. But I have a problem when accessing data.

data1 db 1
data2 db 2
entry:
mov eax, [data1] ;???

Can I access data1 relative from instruction "mov eax, [data1]"? Or is there a way to access data in such problem?
Thanks before..

14 Jun 2016, 11:36

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20447
Location: In your JS exploiting you and your system

revolution 14 Jun 2016, 12:07

In 32-bit code there are no EIP relative memory instructions. So you have to load a GP register with the current EIP and use that to access memory:

Code:

data1 db 1
call my_eip
my_eip:
pop ebx  ;get current EIP
mov al,[ebx+data1-my_eip]

But this won't work if the offset from data1 to my_eip is not fixed. In that case you would need to relocate in some way.

14 Jun 2016, 12:07

DOS386

Joined: 08 Dec 2006
Posts: 1905

DOS386 06 Jul 2016, 09:41

> so the code must can be run in any addresses of memory

Bisa Smile

PIC (position independent code) http://board.flatassembler.net/topic.php?t=11170

_________________
Bug Nr.: 12345

Title: Hello World program compiles to 100 KB !!!

Status: Closed: NOT a Bug

06 Jul 2016, 09:41

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