Using NtRaiseHardError to display a MessageBox

MessageBox.cs

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace Undocumented.Windows
{
    public static unsafe class MessageBox
    {
        // http://undocumented.ntinternals.net/index.html?page=UserMode%2FUndocumented%20Functions%2FError%2FNtRaiseHardError.html
        private static readonly delegate* unmanaged[Stdcall]<uint, uint, uint, uint*, uint, uint*, uint> _ntRaiseHardError;

        static MessageBox()
        {
            var ntdll = NativeLibrary.Load("ntdll.dll");

            _ntRaiseHardError =
                (delegate* unmanaged[Stdcall]<uint, uint, uint, uint*, uint, uint*, uint>)
                NativeLibrary.GetExport(ntdll, "NtRaiseHardError");
        }

        public static int Show(string text, string caption, uint type)
        {
            // used when: MessageBoxW(null, text, caption, MB_DEFAULT_DESKTOP_ONLY | MB_SERVICE_NOTIFICATION)
            // more advanced message boxes can be created with NtUserCreateWindow
            if (caption == null)
            {
                // https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-messagebox
                // The dialog box title. If this parameter is NULL, the default title is Error.
                caption = "Error";
            }

            if (text == null)
            {
                // no text
                // handle gracefully
                text = string.Empty;
            }

            fixed (char* textPointer = text)
            {
                fixed (char* captionPointer = caption)
                {
                    var textBuffer = new UnicodeString
                    {
                        Buffer = textPointer,
                        Length = (ushort)(text.Length * sizeof(char)),
                        MaximumLength = (ushort)(text.Length * sizeof(char))
                    };

                    var captionBuffer = new UnicodeString
                    {
                        Buffer = captionPointer,
                        Length = (ushort)(caption.Length * sizeof(char)),
                        MaximumLength = (ushort)(caption.Length * sizeof(char))
                    };

                    // the 4th (index 3) parameter can optionally be message box timeout value
                    var parameters = stackalloc nint[]
                    {
                        (nint)(&textBuffer),
                        (nint)(&captionBuffer),
                        (nint)type
                    };

                    Unsafe.SkipInit(out uint response);

                    var status = _ntRaiseHardError(
                        0x50000018u, // NtStatus -> STATUS_SERVICE_NOTIFICATION (0x40000018u) | HARDERROR_OVERRIDE_ERRORMODE (0x10000000u)
                        3u, // length of parameters array
                        3u, // always 3
                        (uint*)parameters,
                        default, // turns out to be OptionOk for default which is 0 i believe.
                        &response);

                    if (status != 0)
                    {
                        // error
                        // https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-messagebox
                        // msdn: If the function fails, the return value is zero. To get extended error information, call GetLastError.
                        // SetLastError with RtlNtStatusToDosError

                        return 0;
                    }

                    return (int)response;
                }
            }
        }

        internal struct UnicodeString
        {
            public ushort Length;
            public ushort MaximumLength;
            public char* Buffer;
        }
    }
}