Win64 Global Hook Problem

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TimK

Joined: 14 Feb 2010
Posts: 20

TimK

Why this code crashes Windows?:

Code:

format PE64 GUI 5.0 DLL

...

proc MessageHookProc nCode:DWORD,wParam:QWORD,lParam:QWORD

  invoke  CallNextHookEx, [MessageHook],ecx,rdx,r8

  ret
endp

...

;invoke SetWindowsHookEx, WH_CALLWNDPROC,MessageHookProc,[HInstance],0
;MessageHook dq 0

But this works?:

Code:

proc MessageHookProc nCode:DWORD,wParam:QWORD,lParam:QWORD

  mov [nCode],ecx
  mov [wParam],rdx
  mov [lParam],r8

  invoke  CallNextHookEx, [MessageHook],[nCode],[wParam],[lParam]

  ret
endp

18 Feb 2010, 03:02

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17943
Location: In your JS exploiting you and your system

revolution

Check out the fastcall standard and then compare that to the registers you have used. Now look at the invoke macro code and see what code is generated.

The fastcall macro works forward through the parameters so you can't put them in that order because the values are overwritten before they are used. It is a 'gotcha' in the macros.

If you look at the generated code you should see this:

Code:

;    fastcall function,[value],rcx,rdx,r8
        sub     rsp,0x20
    mov     rcx,[value]
 mov     rdx,rcx
     mov     r8,rdx
      mov     r9,r8
       call    [function]

18 Feb 2010, 05:35

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17943
Location: In your JS exploiting you and your system

revolution

NOTE: this particular problem can be solved by working backwards through the parameters. But it would still not be a general solution. Best would be if the macros gave an error when a register is used as source data after being overwritten.

18 Feb 2010, 05:47

TimK

Joined: 14 Feb 2010
Posts: 20

TimK

That is, temporary storage is required anyway, even without invoke... Thanks!

18 Feb 2010, 06:04

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17943
Location: In your JS exploiting you and your system

revolution

TimK wrote:

That is, temporary storage is required anyway, even without invoke...

No, you can do it without temporary storage.

Code:

;   fastcall function,[value],rcx,rdx,r8
        sub     rsp,0x20
    mov     r9,r8
       mov     r8,rdx
      mov     rdx,rcx
     mov     rcx,[value]
 call    [function]

But the current macro won't do that for you. You have to do it manually.

18 Feb 2010, 06:11

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