Read EFI Variable

EFIVariableRead.cs

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Text;

namespace ConsoleApp2
{
    internal class Program
    {
        // code must be ran as admin
        static void Main()
        {
            Type privilegeType;
            if (RuntimeInformation.FrameworkDescription.Contains("Framework"))
            {
                privilegeType = Type.GetType("System.Security.AccessControl.Privilege");
            }
            else
            {
                // on .NET Core, add the System.Security.AccessControl nuget package otherwise null will be returned
                privilegeType = Type.GetType("System.Security.AccessControl.Privilege, System.Security.AccessControl");
            }

            var privilege = Activator.CreateInstance(privilegeType, "SeSystemEnvironmentPrivilege");
            privilegeType.GetMethod("Enable").Invoke(privilege, null);

            var inputSize = 256;
            var ptr = Marshal.AllocHGlobal(inputSize);
            try
            {
                var outputSize = GetFirmwareEnvironmentVariable("PlatformLangCodes", "{8be4df61-93ca-11d2-aa0d-00e098032b8c}", ptr, inputSize);
                if (Marshal.GetLastWin32Error() != 0)
                    throw new Win32Exception(Marshal.GetLastWin32Error());

                Console.WriteLine(ToHexaDump(ptr, outputSize));
            }
            finally
            {
                Marshal.FreeHGlobal(ptr);
                privilegeType.GetMethod("Revert").Invoke(privilege, null);
            }
        }

        [DllImport("kernel32", CharSet = CharSet.Unicode, SetLastError = true)]
        private static extern int GetFirmwareEnvironmentVariable(string lpName, string lpGuid, IntPtr pBuffer, int nSize);

        public static string ToHexaDump(IntPtr ptr, int bufferSize, bool addHeader = true)
        {
            if (ptr == IntPtr.Zero)
                throw new ArgumentException(null, nameof(ptr));

            if (bufferSize < 0)
                throw new ArgumentOutOfRangeException(nameof(bufferSize));

            var sb = new StringBuilder();
            if (addHeader)
            {
                //             0         1         2         3         4         5         6         7
                //             01234567890123456789012345678901234567890123456789012345678901234567890123456789
                sb.AppendLine("Offset    00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F  0123456789ABCDEF");
                sb.AppendLine("--------  -----------------------------------------------  ----------------");
            }

            for (var i = 0; i < bufferSize; i += 16)
            {
                sb.AppendFormat("{0:X8}  ", i);

                int j;
                for (j = 0; (j < 16) && ((i + j) < bufferSize); j++)
                {
                    sb.AppendFormat("{0:X2} ", Marshal.ReadByte(ptr, i + j));
                }

                sb.Append(' ');
                if (j < 16)
                {
                    sb.Append(new string(' ', 3 * (16 - j)));
                }

                for (j = 0; j < 16 && (i + j) < bufferSize; j++)
                {
                    var b = Marshal.ReadByte(ptr, i + j);
                    if (b > 31 && b < 128)
                    {
                        sb.Append((char)b);
                    }
                    else
                    {
                        sb.Append('.');
                    }
                }
                sb.AppendLine();
            }
            return sb.ToString();
        }
    }
}