Get PEB64 without using P/Invoke

gistfile1.txt

using System;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text;

namespace ConsoleApp1
{
	unsafe class Program
	{
		static void Main(string[] args)
		{
			var methodHandle = typeof(Program).GetMethod(nameof(GetPebPtr), BindingFlags.Static | BindingFlags.NonPublic).MethodHandle;
			RuntimeHelpers.PrepareMethod(methodHandle);
			var methodPointer = methodHandle.GetFunctionPointer().ToPointer();
			var patchStub = stackalloc byte[]
			{
				0x48, 0x31, 0xC0,													// xor rax,rax
				0x65, 0x48, 0xA1, 0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,	// mov rax, gs:[60h]
				0xC3																// ret
			};
			var jitJmpToPreStubOffset = *(int*)((byte*)methodPointer + 1);
			var patchAddress = (byte*)methodPointer + 5 /*jmp offset counted starting from next instruction, so skip jmp 5-bytes sequence*/  + jitJmpToPreStubOffset;
			Unsafe.CopyBlock(patchAddress, patchStub, 15); // copy patch stub bytes to the begining of method's pre-stub (there must be enough space for that in case of using as method body "throw new NotImplementedException()")
			var pPeb = GetPebPtr();
			var peb = *(PEB*)pPeb;
			var pPebEntry = (LDR_DATA_TABLE_ENTRY*)peb.Ldr->InMemoryOrderModuleList.Flink;
			var pebEntry = *pPebEntry;
			var pHeadEntry = pPebEntry;
			while (true)
			{
				pPebEntry = (LDR_DATA_TABLE_ENTRY*)pebEntry.InMemoryOrderLinks.Flink; //pebEntry.InMemoryOrderLinks.Flink.ReinterpretAs<LDR_DATA_TABLE_ENTRY>();
				pebEntry = *pPebEntry;
				if (pPebEntry != pHeadEntry && pebEntry.DllBase != IntPtr.Zero)
				{
					var dllName = Encoding.Unicode.GetString((byte*)pebEntry.BaseDllName.Buffer, pebEntry.BaseDllName.Length);
					var dllImageBase = pebEntry.DllBase;
					var dllPath = Encoding.Unicode.GetString((byte*)pebEntry.FullDllName.Buffer, pebEntry.FullDllName.Length);
					continue;
				}
				break;
			}

			Console.ReadKey();
		}

		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)]
		private static IntPtr GetPebPtr()
		{
			throw new NotImplementedException();
		}
	}

	unsafe struct LIST_ENTRY
	{
		public byte* Flink;
		public byte* Blink;
	}

	struct PEB_LDR_DATA
	{
		private byte Reserved1a;
		private byte Reserved1b;
		private byte Reserved1c;
		private byte Reserved1d;
		private byte Reserved1e;
		private byte Reserved1f;
		private byte Reserved1g;
		private byte Reserved1h;
		private IntPtr Reserved2a;
		private IntPtr Reserved2b;
		private IntPtr Reserved2c;
		public LIST_ENTRY InMemoryOrderModuleList;
	}

	unsafe struct PEB
	{
		private byte Reserved1a;
		private byte Reserved1b;
		private byte BeingDebugged;
		private byte Reserved2a;
		private byte Reserved2b;
		private IntPtr Reserved3a;
		private IntPtr Reserved3b;
		public PEB_LDR_DATA* Ldr;
	}

	unsafe struct UNICODE_STRING
	{
		public ushort Length;
		public ushort MaximumLength;
		public char* Buffer;
	}

	struct LDR_DATA_TABLE_ENTRY
	{
		public LIST_ENTRY InMemoryOrderLinks;
		public LIST_ENTRY InInitializationOrderList;
		public IntPtr DllBase;
		public IntPtr EntryPoint;
		private IntPtr Reserved3;
		public UNICODE_STRING FullDllName;
		public UNICODE_STRING BaseDllName;
	}
}