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-rw-r--r--FatPkg/EnhancedFatDxe/Fat.h16
-rw-r--r--FatPkg/EnhancedFatDxe/FatFileSystem.h2
-rw-r--r--FatPkg/EnhancedFatDxe/FileSpace.c1
-rw-r--r--FatPkg/EnhancedFatDxe/Init.c62
-rw-r--r--FatPkg/FatPei/FatLiteAccess.c69
-rw-r--r--FatPkg/FatPei/FatLiteFmt.h7
6 files changed, 147 insertions, 10 deletions
diff --git a/FatPkg/EnhancedFatDxe/Fat.h b/FatPkg/EnhancedFatDxe/Fat.h
index fb6699061e..525393dbd4 100644
--- a/FatPkg/EnhancedFatDxe/Fat.h
+++ b/FatPkg/EnhancedFatDxe/Fat.h
@@ -975,6 +975,22 @@ FatComputeFreeInfo (
IN FAT_VOLUME *Volume
);
+/**
+
+ Get the FAT entry value of the volume, which is identified with the Index.
+
+ @param Volume - FAT file system volume.
+ @param Index - The index of the FAT entry of the volume.
+
+ @return The value of the FAT entry.
+
+**/
+UINTN
+FatGetFatEntry (
+ IN FAT_VOLUME *Volume,
+ IN UINTN Index
+ );
+
//
// Init.c
//
diff --git a/FatPkg/EnhancedFatDxe/FatFileSystem.h b/FatPkg/EnhancedFatDxe/FatFileSystem.h
index 60b9c56b71..3bad7fceea 100644
--- a/FatPkg/EnhancedFatDxe/FatFileSystem.h
+++ b/FatPkg/EnhancedFatDxe/FatFileSystem.h
@@ -35,6 +35,8 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
#define FAT_CLUSTER_SPECIAL_FAT32 0x0FFFFFF7
#define FAT_CLUSTER_MASK_FAT12 0xFFF
#define FAT_CLUSTER_UNMASK_FAT12 0xF000
+#define FAT_CLUSTER_MASK_FAT16 0xFFFF
+#define FAT_CLUSTER_UNMASK_FAT16 0xF0000
#define FAT_CLUSTER_MASK_FAT32 0x0FFFFFFF
#define FAT_CLUSTER_UNMASK_FAT32 0xF0000000
#define FAT_POS_FAT12(a) ((a) * 3 / 2)
diff --git a/FatPkg/EnhancedFatDxe/FileSpace.c b/FatPkg/EnhancedFatDxe/FileSpace.c
index 909d4980d2..6852c3ea00 100644
--- a/FatPkg/EnhancedFatDxe/FileSpace.c
+++ b/FatPkg/EnhancedFatDxe/FileSpace.c
@@ -80,7 +80,6 @@ FatLoadFatEntry (
@return The value of the FAT entry.
**/
-STATIC
UINTN
FatGetFatEntry (
IN FAT_VOLUME *Volume,
diff --git a/FatPkg/EnhancedFatDxe/Init.c b/FatPkg/EnhancedFatDxe/Init.c
index 9c51ed5b7b..f020cf703d 100644
--- a/FatPkg/EnhancedFatDxe/Init.c
+++ b/FatPkg/EnhancedFatDxe/Init.c
@@ -96,14 +96,6 @@ FatAllocateVolume (
}
//
- // Initialize cache
- //
- Status = FatInitializeDiskCache (Volume);
- if (EFI_ERROR (Status)) {
- goto Done;
- }
-
- //
// Install our protocol interfaces on the device's handle
//
Status = gBS->InstallMultipleProtocolInterfaces (
@@ -237,6 +229,7 @@ FatOpenDevice (
UINTN SectorsPerFat;
UINT8 SectorsPerClusterAlignment;
UINT8 BlockAlignment;
+ UINTN ReservedFatEntry;
//
// Read the FAT_BOOT_SECTOR BPB info
@@ -423,7 +416,58 @@ FatOpenDevice (
// We are now defining FAT Type
//
Volume->FatType = FatType;
- ASSERT (FatType != FatUndefined);
+
+ //
+ // Initialize cache before we use the helper functions that hit the cache
+ //
+ Status = FatInitializeDiskCache (Volume);
+ if (EFI_ERROR (Status)) {
+ return Status;
+ }
+
+ //
+ // Check the reserved FAT entries to ensure they contain valid values
+ //
+ ReservedFatEntry = FatGetFatEntry (Volume, 0);
+ if (Volume->FatEntryBuffer == MAX_UINT32) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ // Reserved FAT entry 0 should contain the BPB_MEDIA byte value in the low 8 bits with all other bits set to 1
+ switch (FatType) {
+ case Fat12:
+ if ((ReservedFatEntry & FAT_CLUSTER_MASK_FAT12) != ((UINTN)FatBs.FatBsb.Media | 0xF00)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ break;
+
+ case Fat16:
+ if ((ReservedFatEntry & FAT_CLUSTER_MASK_FAT16) != ((UINTN)FatBs.FatBsb.Media | 0xFF00)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ break;
+
+ case Fat32:
+ // the upper 4 bits of a FAT32 entry are reserved, so are unchecked here
+ if ((ReservedFatEntry & FAT_CLUSTER_MASK_FAT32) != ((UINTN)FatBs.FatBsb.Media | 0x0FFFFF00)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ break;
+
+ default:
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ // Reserved FAT entry 1 should contain the end of chain mark. On FAT16 and FAT32, the high 2 bits may be used as
+ // dirty and hardware error bits, so are ignored in this check, but FatGetFatEntry already ignores them to unify the
+ // logic across FAT types
+ ReservedFatEntry = FatGetFatEntry (Volume, 1);
+ if ((Volume->FatEntryBuffer == MAX_UINT32) || !FAT_END_OF_FAT_CHAIN (ReservedFatEntry)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
return EFI_SUCCESS;
}
diff --git a/FatPkg/FatPei/FatLiteAccess.c b/FatPkg/FatPei/FatLiteAccess.c
index 10df4516b2..46a7563ab6 100644
--- a/FatPkg/FatPei/FatLiteAccess.c
+++ b/FatPkg/FatPei/FatLiteAccess.c
@@ -43,6 +43,7 @@ FatGetBpbInfo (
UINT64 FatLba;
UINT64 RootLba;
UINT64 FirstClusterLba;
+ UINT32 ReservedFatEntries[2];
//
// Read in the BPB
@@ -167,6 +168,74 @@ FatGetBpbInfo (
Volume->FatType = Volume->MaxCluster < 4085 ? Fat12 : Fat16;
}
+ //
+ // Read reserved FAT entries which are the first two entries from FatPos
+ //
+ Status = FatReadDisk (
+ PrivateData,
+ Volume->BlockDeviceNo,
+ Volume->FatPos,
+ (Volume->FatType == Fat32) ? sizeof (UINT32) * 2 : sizeof (UINT16) * 2,
+ ReservedFatEntries
+ );
+ if (EFI_ERROR (Status)) {
+ return Status;
+ }
+
+ //
+ // Reserved FAT entry 0 should contain the BPB_MEDIA byte value in the low 8 bits with all other bits set to 1
+ // Reserved FAT entry 1 should contain the end of chain mark. On FAT16 and FAT32, the high 2 bits may be used as
+ // dirty and hardware error bits, so are ignored in this check
+ //
+ switch (Volume->FatType) {
+ case Fat12:
+ // we read two entries and in FAT12, each entry is 12 bits, so we need to shift the first entry by 20 bits to
+ // only read it and not the second entry and beyond
+ if (((ReservedFatEntries[0] >> 20) & FAT_CLUSTER_MASK_FAT12) != ((UINTN)Bpb.Media | 0xF00)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ // the second entry starts 12 bits in and is 12 bits in length, so we shift by 8 bits to remove the start of the
+ // third entry and then mask to only read the second entry
+ if (!FAT_CLUSTER_END_OF_CHAIN (ReservedFatEntries[0] >> 8)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ break;
+
+ case Fat16:
+ // in FAT16, each entry is 16 bits, so the first entry is the upper 16 bits of ReservedFatEntries[0]
+ if (((ReservedFatEntries[0] >> 16) & FAT_CLUSTER_MASK_FAT16) != ((UINTN)Bpb.Media | 0xFF00)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ // the second entry is simply the lower 16 bits of ReservedFatEntries[0], however, we must ignore the upper two
+ // bits. For the purposes of checking if the EOC mark exists, we treat those two bits as 1
+ if (!FAT_CLUSTER_END_OF_CHAIN ((ReservedFatEntries[0] & 0x3FFF) | 0xC000)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ break;
+
+ case Fat32:
+ // the upper 4 bits of a FAT32 entry are reserved, so are unchecked here
+ // FAT32 has 32 bit entries, so the first entry is ReservedFatEntries[0]
+ if ((ReservedFatEntries[0] & FAT_CLUSTER_MASK_FAT32) != ((UINTN)Bpb.Media | 0x0FFFFF00)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ // the second entry is simply ReservedFatEntries[1], but we must ignore the upper two bits. For the purposes of
+ // checking if the EOC mark exists, we treat those two bits as 1
+ if (!FAT_CLUSTER_END_OF_CHAIN ((ReservedFatEntries[1] & 0x3FFFFFFF) | 0xC0000000)) {
+ return EFI_VOLUME_CORRUPTED;
+ }
+
+ break;
+
+ default:
+ return EFI_VOLUME_CORRUPTED;
+ }
+
return EFI_SUCCESS;
}
diff --git a/FatPkg/FatPei/FatLiteFmt.h b/FatPkg/FatPei/FatLiteFmt.h
index fef70fe1de..b179b5f95f 100644
--- a/FatPkg/FatPei/FatLiteFmt.h
+++ b/FatPkg/FatPei/FatLiteFmt.h
@@ -27,6 +27,13 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
#define FAT_CLUSTER_BAD (FAT_CLUSTER_SPECIAL)
#define FAT_CLUSTER_LAST (-1)
+#define FAT_CLUSTER_MASK_FAT12 0xFFF
+#define FAT_CLUSTER_UNMASK_FAT12 0xF000
+#define FAT_CLUSTER_MASK_FAT16 0xFFFF
+#define FAT_CLUSTER_UNMASK_FAT16 0xF0000
+#define FAT_CLUSTER_MASK_FAT32 0x0FFFFFFF
+#define FAT_CLUSTER_UNMASK_FAT32 0xF0000000
+
#define DELETE_ENTRY_MARK 0xE5
#define EMPTY_ENTRY_MARK 0x00
generated by cgit (git 2.34.1) at 2025-02-23 06:48:50 +0000