API Hook funktioniert nicht global

[Neutral General]

Ja doch.. Oder nicht?!

DLL:

Delphi-Quellcode:

library HookDLL;

uses
  Windows,
  SysUtils,
  Classes,
  HookUtils in 'HookUtils.pas';

{$R *.res}

var
  FHook: HHOOK = 0;
  FHooked: Boolean = false;

function NewIsClipboardFormatAvailable(AFormat: Cardinal): BOOL; stdcall;
begin
  Result := true;
end;

function HookIsClipboardFormatAvailable: Boolean;
var func: Pointer;
    hProc: THandle;
    jmp: TJump;
    bw: Cardinal;
begin
  func := GetProcPtr('user32.dll','IsClipboardFormatAvailable');

  hProc := GetCurrentProcess;
  try
    jmp := Jump(@NewIsClipboardFormatAvailable);
    WriteProcessMemory(hProc,func,@jmp,SizeOf(TJump),bw);
    Result := bw = SizeOf(TJump);
  finally
    CloseHandle(hProc);
  end;
end;

function HookProc(code: Integer; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
begin
  if FHook <> 0 then
  begin
    if code < HC_ACTION then
      Result :=  CallNextHookEx(FHook,code,wParam,lParam)
    else
    begin
      if (not FHooked) and (code >= HC_ACTION) then
      begin
        FHooked := true;
        HookIsClipboardFormatAvailable;
      end;
      Result := CallNextHookEx(FHook,code,wParam,lParam);
    end;
  end
  else
    Result := 0;
end;

procedure InstallHook; stdcall;
begin
  FHook := SetWindowsHookEx(WH_GETMESSAGE,HookProc,hInstance,0);
end;

procedure UnInstallHook; stdcall;
begin
  if FHook <> 0 then
    UnhookWindowsHookEx(FHook);
end;

exports
  InstallHook,
  UnInstallHook,
  HookProc;

begin

end.

HookUtils:

Delphi-Quellcode:

unit HookUtils;

interface

uses
  Windows;

type
  TJump = packed record
    Push: Byte;
    Dest: Pointer;
    Retn: Byte;
    Nops: Array[0..3] of Byte;
  end;

  function Jump(ADest: Pointer): TJump;
  function GetProcPtr(ADll: String; AProc: String): Pointer;

implementation

function Jump(ADest: Pointer): TJump;
begin
  Result.Push := $68;
  Result.Dest := ADest;
  Result.Retn := $C3;
  FillChar(Result.Nops[0],SizeOf(Result.Nops),$90);
end;

function GetProcPtr(ADll: String; AProc: String): Pointer;
var hLib: HModule;
begin
  hLib := LoadLibrary(PChar(ADll));
  if hLib <> 0 then
  begin
    try
      Result := GetProcAddress(hLib,PChar(AProc));
    finally
      FreeLibrary(hLib);
    end;
  end
  else
    Result := nil;
end;

end.

Oder hab ich da tatsächlich grundlegend etwas nicht verstanden?!
Jetzt bin ich verwirrt.