how to push a string address to stack with assembly, machine code
- by Yigit
Hi all,
I am changing minesweeper.exe in order to have an understanding of how code injection works. Simply, I want the minesweeper to show a message box before starting. So, I find a "cave" in the executable and then define the string to show in messagebox and call the messagebox. Additionally of course, I have to change the value at module entry point of the executable and first direct it to my additional code, then continue its own code.
So at the cave what I do;
"hello starbuck",0
push 0 //arg4 of MessageBoxW function
push the address of my string //arg3, must be title
push the address of my string //arg2, must be the message
push 0 //arg1
call MessageBoxW
...
Now since the memory addresses of codes in the executable change everytime it is loaded in the memory, for calling the MessageBoxW function, I give the offset of the address where MessageBoxW is defined in Import Address Table. For instance, if MessageBoxW is defined at address1 in the IAT and the instruction just after call MessageBoxW is at address2
instead of writing call MessageBoxW, I write call address2 - address1.
So my question is, how do I do it for pushing the string's address to the stack?
For example, if I do these changes via ollydbg, I give the immediate address of "hello starbuck" for pushing and it works. But after reloading the executable or starting it outside of ollydbg, it naturally fails, since the immediate addresses change.
Thanks in advance,
Yigit.
