Stack frames in Delphi

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CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 22 Feb 2014, 18:52

32-bit Delphi

Code:

push ebp
mov ebp,esp
sub esp,N*4
;...
mov ecx,[ebp] ; Previous EBP
;...
pop ebp
ret

64-bit Delphi

Code:

push rbp
sub rsp,N*8
mov rbp,rsp
;...
mov rcx,? ; Previous RBP
;...
lea rsp,[rbp+N*8]
pop rbp
ret

How to get pointer to previous RBP if don't know what N is equal?

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22 Feb 2014, 18:52

tthsqe

Joined: 20 May 2009
Posts: 767

tthsqe 22 Feb 2014, 23:54

Unclear what you are trying to do in these examples.
If you don't know N, how can you write sub rsp,N*8 and lea rsp,[rbp+N*8]? Clearly who/whatever wrote these two instructions would know N.

22 Feb 2014, 23:54

typedef

Joined: 25 Jul 2010
Posts: 2893
Location: 0x77760000

typedef 23 Feb 2014, 06:00

@CandyMan From what I can tell, you need to read this :

http://msdn.microsoft.com/en-us/library/7kcdt6fy.aspx

http://msdn.microsoft.com/en-us/library/9b372w95.aspx

http://msdn.microsoft.com/en-us/library/zthk2dkh.aspx

23 Feb 2014, 06:00

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 23 Feb 2014, 12:09

I would like to write exception call stack unit. In 32-bit mode there is no problem.

23 Feb 2014, 12:09

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 23 Feb 2014, 12:25

If Delphi always uses the same prolog code then you can use the function address and read the contents of the value of N from the encoding:

Code:

push rbp        ;db 0x55
sub rsp,3*8     ;db 0x48,0x83,0ec, db N*8       <--- byte values from -128 to +124

push rbp        ;db 0x55
sub rsp,30*8    ;db 0x48,0x81,0ec, dd N*8       <--- dword values from -2G to +2G

23 Feb 2014, 12:25

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 23 Feb 2014, 12:51

CandyMan,

That'll probably take some efforts to implement it right. Given this simple program, Delphi XE5 generates peculiar x86-64 code:

Code:

{$APPTYPE CONSOLE}
program HelloWorld;
  procedure Say(a0, a1, a2, a3: LongInt; const It: string);
    procedure SayIt(b0: LongInt);
      procedure ReallySayIt(c0: LongInt);
        procedure SayItAtOnceYouDummKopf(d0: LongInt); begin WriteLn(It); end;
      begin SayItAtOnceYouDummKopf(3); end;
    begin ReallySayIt(2); end;
  begin SayIt(1); end;
begin
  Say(0, 0, 0, 0, 'Hello, world!');
end.

Not to mention intermittent nops and xor r#,r# instead of shorter xor e#, e#, it does pass enclosing rbp as a hidden argument to the nested routines (__thiscall Wink

23 Feb 2014, 12:51

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