From 56f3d2696985c7824cae6befa254ed51547322fc Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Mon, 10 Jul 2023 14:54:55 +0200
Subject: [PATCH] kernel+libluna: Fix the CRC32 algorithm and use it to verify
 the GPT header

---
 kernel/src/fs/GPT.cpp | 2 --
 libluna/src/CRC32.cpp | 4 +---
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/src/fs/GPT.cpp b/kernel/src/fs/GPT.cpp
index 713be6dd..9a5c1d78 100644
--- a/kernel/src/fs/GPT.cpp
+++ b/kernel/src/fs/GPT.cpp
@@ -29,7 +29,6 @@ namespace GPT
         check(header.reserved == 0);
         check(header.this_lba == 1);
 
-#if 0
         const u32 chksum = checksum_gpt(header);
 
         if (chksum != header.checksum)
@@ -37,7 +36,6 @@ namespace GPT
             kwarnln("gpt: Header checksum does not match, %#.8x != %#.8x!", chksum, header.checksum);
             return false;
         }
-#endif
 
         u64 partition_table_start = header.partition_table_lba * GPT_SECTOR_SIZE;
 
diff --git a/libluna/src/CRC32.cpp b/libluna/src/CRC32.cpp
index 31965739..d23ff684 100644
--- a/libluna/src/CRC32.cpp
+++ b/libluna/src/CRC32.cpp
@@ -35,15 +35,13 @@ static const u32 crc_table[] = {
 
 namespace CRC32
 {
-    // FIXME: This shouldn't return 0xffffffff when there are 4 zeros in a row somewhere in the data, right? That's what
-    // happens to the GPT header. (other CRC32 implementations don't seem to have this problem)
     u32 checksum(const u8* data, usize size)
     {
         u32 crc = 0xffffffffu;
 
         for (usize i = 0; i < size; i++)
         {
-            const u32 index = (crc & data[i]) & 0xff;
+            const u32 index = (crc & 0xff) ^ data[i];
             crc = (crc >> 8) ^ (crc_table[index]);
         }