How to access the stack below 4k?

Index > Windows > How to access the stack below 4k?

Author

Thread

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz 21 Aug 2012, 10:59

Hi, is there any way to increase stack size ?
For example, AFAIK stack is MAX 4KB for current process. How can I increase it like I could have more than 4KB (1MB for example.)
If you don't understand what I mean, here's code and sorry for English.

Code:

push ebp
mov ebp,esp
sub esp,10000h
mov dword[esp],1 <-- crash.

Thanks.

21 Aug 2012, 10:59

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 21 Aug 2012, 11:41

Can we asusme you are coding for Windows? It looks as though you are. So based upon that assumption, you will have to play nicely with the stack guard mechanism used in Windows. You have to "touch" the stack somewhere in each page boundary to trigger the guard bit and allocate a new page from the reserved pool. And depending upon your assembly setting your reserved stack size can be as large as the memory system allows:

Code:

format pe ...
stack ??? ;put you stack size here if you want more or less than the default size

;...

;now touch the stack

mov al,byte[esp-4096*1] ;or rsp for 64-bit
mov al,byte[esp-4096*2]
mov al,byte[esp-4096*3]
mov al,byte[esp-4096*4]
mov al,byte[esp-4096*5]
mov al,byte[esp-4096*6]
;etc.

I'll leave it up to you to code whatever loops and things that suit your actual code

21 Aug 2012, 11:41

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz 21 Aug 2012, 12:05

Hi, thanks for reply but I tried it and program still crashes.. used really huge value for stack, look example:

Code:

stack 1000000h
...
push ebp,
mov ebp,esp
sub esp,10000h
mov dword[esp],1 ;<-- still crashes..

and yes, I'm working in Windows environment.

21 Aug 2012, 12:05

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 21 Aug 2012, 12:07

You have to touch the stack as in my example code above. You can't simply go straight to the lowest stack address, it will always crash as you found out.

21 Aug 2012, 12:07

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz 21 Aug 2012, 12:13

hmm, thanks revolution! still, one last question.
I'm using file directive in local variables and that's the reason of crashing program. Isn't there other way to define it there ? I'm just playing with stack and trying to understand it more deeper.

21 Aug 2012, 12:13

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 21 Aug 2012, 12:20

Overflowz wrote:

I'm using file directive in local variables ...

Sorry, I only support sane uses of the assembler.

21 Aug 2012, 12:20

AsmGuru62

Joined: 28 Jan 2004
Posts: 1625
Location: Toronto, Canada

AsmGuru62 21 Aug 2012, 13:37

stack directive has TWO parameters:

Code:

stack 100000h,100000h

The above will produce 1Mb stack without guard pages.

21 Aug 2012, 13:37

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz 22 Aug 2012, 13:17

Thanks AsmGuru62! That's what I was looking for.

22 Aug 2012, 13:17

bzdashek

Joined: 15 Feb 2012
Posts: 147
Location: Tolstokvashino, Russia

bzdashek 23 Aug 2012, 15:07

revolution wrote:

Overflowz wrote:
I'm using file directive in local variables ...
Sorry, I only support sane uses of the assembler.

Your profile's location states otherwise. Very Happy

23 Aug 2012, 15:07

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum