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Function return value and code cave

 
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catshy
How do I cheat?
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Joined: 01 Feb 2019
Posts: 9
PostPosted: Wed Jul 29, 2020 4:34 am    Post subject: Function return value and code cave Reply with quote
Hello,

I have question about code cave via CE.

If I have function and I know address of this function, for example:

Code:

function func(int arg)
{
  return arg+1;
}

MessageBox(  func(10)  );



And now:

1. How to get func() return value before this function send it to MessageBox

2. How to change return value before func() send it to MB - like swip.

Thanks!
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Csimbi
I post too much
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Joined: 14 Jul 2007
Posts: 3327
PostPosted: Wed Jul 29, 2020 9:44 am    Post subject: Reply with quote
1.
allocate a memory for a var.
register the var.
Then store the val into the var before the return.

2.
change it before the return
it is there somewhere in the stack, at esp or esp+04.
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catshy
How do I cheat?
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Joined: 01 Feb 2019
Posts: 9
PostPosted: Wed Jul 29, 2020 1:14 pm    Post subject: Reply with quote
@Csimbi, thanks for answer!

Could u show me example code for point 1. ?
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Csimbi
I post too much
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Joined: 14 Jul 2007
Posts: 3327
PostPosted: Thu Jul 30, 2020 4:27 am    Post subject: Reply with quote
I usually allocate a single block, some peeps use globalalloc for each var.
Each have their own benefits.
Code:
[enable]
alloc(newmem,4096)

label (var)
registersymbol(var)

newmem:
var:
dd 0

[disable]
unregistersymbol(var)

dealloc(newmem)
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