NOP'ing address in MW3

[exploder2013]

Hello. I am trying to get unlimited ammo in MW3. I've found address in ollydbg and all I need to do is NOP it. But for some kind of reason game always crashes when I try to NOP it.

Address itself in OllyDbg is on the image I attached.

Code from injected DLL:

 

#include <windows.h>

void NOP(int Addr, int bytes)
{
	memset( (PVOID)Addr, 0x90, bytes);
}

void Start()
{

	while( !GetAsyncKeyState( VK_INSERT ))
	{
		if( GetAsyncKeyState( VK_F1 ) )
		{
			NOP( 0x4D6832, 4 );
		} else if( GetAsyncKeyState( VK_F2 ) )
		{
			
		}
	}
	
}

INT APIENTRY DllMain(HMODULE hDLL, DWORD Reason, LPVOID Reserved) {

	switch(Reason) {
	case DLL_PROCESS_ATTACH:
		CreateThread( NULL, NULL, (LPTHREAD_START_ROUTINE)Start, hDLL, NULL, NULL);
		break;
	}

	return TRUE;
}

Could someone explain me what I'm doing wrong?

Thanks.

[_PuRe.LucK*]

When does it crash? When you NOP it in olly or in C++ or both?

[exploder2013]

It works fine when I NOP it in Olly, but when I inject DLL and press the hot-key, it immediately crashes.

[abuckau907]

@exploder2013

So you're modifying the code section? Code sections are usually marked EXECUTE_READ , not EXECUTE_READ_WRITE. I think (?).
Does memset() call VirtualProtect() for you? You could call GetLastError() and see if it's something along the lines of "Access Denied" - if so, it's because the mem region is marked read_only. Call VirtualProtect() and set it to EXEC_READ_WRITE (don't forget the EXEC, or it'll crash if the cpu tries to run it as code). Optionall set it back to EXEC_READ when done. Maybe.

First you should figure out exactly which part (admittedly it's not a lot of code) is causing the problem. You say the dll injects correctly, and it only crashes when you press the hot-key? Sounds like the key code is working, and it's failing at the call to NOP(). ? I don't think you're using GetAsyncKeyState() quite correctly (?), but I'm not sure - apparently it's working : ) Since you already have the code checking for the "F2" key, add a call to MessageBox() -- just for testing purposes. If the messagebox displays correctly, then you know 100% the problem is your NOP function.

[exploder2013]

The memory address that I tried to modify was protected. VirtualProtect did the job and now it's working. Thanks.