[Source]Simulate GetWindowsDirectory

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krackwar

Joined: 24 May 2008
Posts: 13
Location: Chile

krackwar 06 Sep 2008, 21:41

Code:

;This source simulate the api GetWindowsDirectory
;Autor:Krackwar 
include 'win32ax.inc'

  .data
  ruta db 0
.code
start:

      buscap:
                inc ebp
                cmp word[ebp],':'
                jne buscap
                sub ebp,2
               unir:
               invoke lstrcat ,ruta,ebp
               add  ebp,2
               cmp word[ebp],'\'
                JE ver
                JNe unir
     mostrar:
      invoke MessageBox,0,ruta,0,0
       push 0
       call[ExitProcess]
       ver:
mov ecx,100h  ;supuesto tamaño de la cadena
mov al,'\'        ;caracter separador
mov edi,ruta
repne scasb    ;compara hasta que se cumpla la condicion
 jne unir
 JE mostrar
       jmp unir
      .end start

06 Sep 2008, 21:41

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 07 Sep 2008, 15:05

krackwar,

Doesn't include 'win32ax.inc' contradicts the cmp word[bp],':'?

Hint: A vs. W. It's always good to try to compile example and run it. Wink

07 Sep 2008, 15:05

krackwar

Joined: 24 May 2008
Posts: 13
Location: Chile

krackwar 08 Sep 2008, 02:40

baldr wrote:

krackwar,

Doesn't include 'win32ax.inc' contradicts the cmp word[bp],':'?

Hint: A vs. W. It's always good to try to compile example and run it.

The code is run....

08 Sep 2008, 02:40

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4623
Location: Argentina

LocoDelAssembly 08 Sep 2008, 03:02

WinXP SP3 without source modification

Code:

---------------------------
Error
---------------------------
C:\WINDOWS
---------------------------
Aceptar   
---------------------------

With baldr suggestion:

Code:

---------------------------
Error
---------------------------
C:\WINDOWS\WinSxs\:\WINDOWS\WinSxs\
---------------------------
Aceptar   
---------------------------

I suppose it works* because lstrcatA is copying char by char and krackwar's algorithm stops at the second slash so this algorithm has some kind of Unicode to ASCII built-in functionality. (If someone can verify my "claims" please do it since I have spent too few time on OllyDgb with this snippet so it is just a guess).

*works in the sense that it shows "C:\WINDOWS" but I'm not assuring that this snippet will always provide the correct path.

08 Sep 2008, 03:02

f0dder

Joined: 19 Feb 2004
Posts: 3174
Location: Denmark

f0dder 08 Sep 2008, 17:01

Code that depends on initial register value on program startup? Yay, that's never going to break.

08 Sep 2008, 17:01

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 27 Sep 2008, 20:03

krackwar wrote:

baldr wrote:
krackwar,

Doesn't include 'win32ax.inc' contradicts the cmp word[bp],':'?

Hint: A vs. W. It's always good to try to compile example and run it.
The code is run....

I do know that it runs. I'm talking about somewhat convoluted way you've done the simple strchr*2/strcpy routine… That jne/je pairs are just marvels! Wink

Don't take it as an offense, though.

There are more to find in userspace, as Windows™ extensively uses it for dirty tricks. Do you want to believe that this will not change at [their] will?

f0dder,

His code depends on previous function's (BaseProcessStart to be exact) stack frame base pointer, that's OK for some time. BP in DOS is as predictable as EBP in Windows™…

_________________
"Don't belong. Never join. Think for yourself. Peace." – Victor Stone.

27 Sep 2008, 20:03

r22

Joined: 27 Dec 2004
Posts: 805

r22 28 Sep 2008, 07:56

Entertaining little hack.

On the same level as GetCurrentProcess always returning -1 and GetCurrentThread always returning -2 (Making the actual api calls dubious).

Take it for whats it's worth, an interesting hacky snippet.

28 Sep 2008, 07:56

f0dder

Joined: 19 Feb 2004
Posts: 3174
Location: Denmark

f0dder 28 Sep 2008, 13:49

r22 wrote:

Entertaining little hack.

On the same level as GetCurrentProcess always returning -1 and GetCurrentThread always returning -2 (Making the actual api calls dubious).

...Until the days they start looking up the values via [FS:xx] instead Razz

(I find it weird that MSDN does mention the value -1, but still say that's how they're currently handled... one shouldn't really be documentation implementation details. MSDN also does say "it is best to call GetCurrentProcess instead of hard-coding this constant value").

r22 wrote:

Take it for whats it's worth, an interesting hacky snippet.

Yeah... cute, but definitely not something you should use outside 4k intros/whatever Smile

_________________
carpe noctem

28 Sep 2008, 13:49

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