Descriptor check.

efi-board-id.cs

@@ -1,41 +1,58 @@
-// David R, 22.02.2023
-// C# code to pull a Mac board-id from compatible EFIROM dumps.
+// ROMHelper.cs - David R - 22.02.2023
+// CSharp.NET code to pull a Mac board-id from compatible EFIROM dumps.
 
 using System;
 using System.IO;
+using System.Text;
 
 namespace MacTools.EFI
 {
  class ROMHelper
  {
- const int BID_OFFSET = 0x1060; // Offset in PDR region, actual board-id is at 0x1064h (BID_OFFSET + BID_POS).
- const int BID_DATA_LEN = 0x12; // Length of the data we want.
- const int BID_POS = 0x4; // Position of board-id.
- const int BID_LEN = 0x8; // Length of board-id (8 bytes).
+ const int BID_DATA_OFFSET = 0x1060; // Offset in PDR region, actual board-id is at 0x1064h (BID_OFFSET + BID_POS).
+ const int BID_DATA_LEN = 0x12;  // Lenth of the data we want.
+ const int BID_POS = 0x4;  // Position of board-id.
+ const int BID_LEN = 0x8;  // Length of board-id (8 bytes).
 
- public static string getBoardIdFromEfiROM(string filePath)
+ private static readonly byte[] hexDescriptor = { 0x5A, 0xA5, 0xF0, 0x0F }; // Descriptor signature
+ private static readonly byte[] hexBoardId = { 0x7C, 0x00, 0x00, 0x19 }; // board-id signature
+
+ public static string strGetBoardIdFromEfiROM(string filePath)
  {
  try
  {
  using (FileStream fileStream = new FileStream(filePath, FileMode.Open))
  {
- using (BinaryReader binaryReader = new BinaryReader(fileStream))
+ using (BinaryReader binaryReader = new BinaryReader(fileStream, Encoding.Unicode))
  {
- string strBcBytes = string.Empty;
- byte[] bIdBytes = new byte[BID_DATA_LEN];
- binaryReader.BaseStream.Position = BID_OFFSET; // Seek to marker offset.
- bIdBytes = binaryReader.ReadBytes(BID_DATA_LEN); // Read 12 bytes (Marker + Board ID in hex).
+ byte[] bytesDescriptor = new byte[0x4];
+ byte[] bytesBoardId = new byte[BID_DATA_LEN];
+
+ binaryReader.BaseStream.Position = 0x10;
+ bytesDescriptor = binaryReader.ReadBytes(0x4);
 
- // Looking for 7C000019h in the first 4 bytes skipping 0x00
- if (bIdBytes[0] == 0x7C && bIdBytes[3] == 0x19)
+ // Compare magic bytes to expected bytes
+ if (bytesDescriptor[0] == hexDescriptor[0] && bytesDescriptor[1] == hexDescriptor[1] &&
+ bytesDescriptor[2] == hexDescriptor[2] && bytesDescriptor[3] == hexDescriptor[3])
  {
- // Found bytes, return the board-id.
- strBcBytes = BitConverter.ToString(bIdBytes, BID_POS, BID_LEN).Replace("-", ""); // Spit out board-id hexadecimal
- return string.Concat("Mac-", strBcBytes); // Return final string
+ binaryReader.BaseStream.Position = BID_DATA_OFFSET;
+ bytesBoardId = binaryReader.ReadBytes(BID_DATA_LEN);
+
+ // Looking for 7C000019h in the first 4 bytes skipping 0x00.
+ if (bytesBoardId[0] == hexBoardId[0] && bytesBoardId[3] == hexBoardId[3])
+ {
+ // Found bytes, return the board-id.
+ string strBcBytes = BitConverter.ToString(bytesBoardId, BID_POS, BID_LEN).Replace("-", ""); // Spit out board-id hexadecimal.
+ return string.Concat("Mac-", strBcBytes); // Return final string
+ }
+ else
+ {
+ return "Expected bytes not found at 0x1060h."; // Expected bytes not found.
+ }
  }
  else
  {
- return "Marker not found at 0x1060h.";
+ return "No descriptor, not a valid binary?"; // Descriptor not found.
  }
  }
  }
@@ -46,4 +63,4 @@ public static string getBoardIdFromEfiROM(string filePath)
  }
  }
  }
-}
+}