From c6d8f7de7042a47f267b6df3d76fc94ce164bc39 Mon Sep 17 00:00:00 2001
From: Pierre Schweitzer <pierre@reactos.org>
Date: Wed, 9 Mar 2011 10:33:13 +0000
Subject: [PATCH] [NTOSKRNL] Implemented FstubFixupEfiPartition(): Purpose is
 to let ReactOS handle realistic partitions length in case of an EFI/GPT
 protective MBR. Indeed, when formatting a disk to GPT, you add a protective
 MBR that contains a fake partition entry, with type 0xEE having the following
 property: its size is set to maximum allocatable size in MBR. In that case,
 if disk is small, you may go beyond disk size. This is why a fix to partition
 length may be needed when re-reading partition entry. This is the way ReactOS
 creates protective MBR. You may find some more information here:
 http://msdn.microsoft.com/en-us/windows/hardware/gg463525

Fixed xHalIoReadPartitionTable():
- Allocate a buffer that has the proper size (instead of allocating a buffer which is too big). Especially since this leads to partial init only some lines after.
- Remove redundant & useless affectation.
- Check/fix 0xEE partition length in case of an EFI/GPT protective MBR (see upper point).

svn path=/trunk/; revision=51002
---
 reactos/ntoskrnl/fstub/disksup.c | 33 ++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/reactos/ntoskrnl/fstub/disksup.c b/reactos/ntoskrnl/fstub/disksup.c
index ce184bcdced..7c4f651f8ff 100644
--- a/reactos/ntoskrnl/fstub/disksup.c
+++ b/reactos/ntoskrnl/fstub/disksup.c
@@ -24,6 +24,8 @@ const WCHAR DiskMountString[] = L"\\DosDevices\\%C:";
 
 #define PARTITION_MAGIC    0xaa55
 
+#define EFI_PMBR_OSTYPE_EFI 0xEE
+
 #include <pshpack1.h>
 
 typedef struct _REG_DISK_MOUNT_INFO
@@ -1358,6 +1360,24 @@ xHalExamineMBR(IN PDEVICE_OBJECT DeviceObject,
     }
 }
 
+VOID
+NTAPI
+FstubFixupEfiPartition(IN PPARTITION_DESCRIPTOR PartitionDescriptor,
+                       IN ULONGLONG MaxOffset)
+{
+    ULONG PartitionLength;
+    PAGED_CODE();
+
+    /* Compute partition length (according to MBR entry) */
+    PartitionLength = PartitionDescriptor->StartingSectorLsb0 + PartitionDescriptor->PartitionLengthLsb0;
+    /* In case the partition length goes beyond disk size... */
+    if (PartitionLength > MaxOffset)
+    {
+        /* Resize partition to its maximum real length */
+        PartitionDescriptor->PartitionLengthLsb0 = MaxOffset - PartitionDescriptor->StartingSectorLsb0;
+    }
+}
+
 NTSTATUS
 FASTCALL
 xHalIoReadPartitionTable(IN PDEVICE_OBJECT DeviceObject,
@@ -1425,7 +1445,7 @@ xHalIoReadPartitionTable(IN PDEVICE_OBJECT DeviceObject,
             MaxOffset, MaxSector);
 
     /* Allocate our buffer */
-    Buffer = ExAllocatePoolWithTag(NonPagedPool, PAGE_SIZE, TAG_FILE_SYSTEM);
+    Buffer = ExAllocatePoolWithTag(NonPagedPool, InputSize, TAG_FILE_SYSTEM);
     if (!Buffer)
     {
         /* Fail, free the input buffer */
@@ -1503,9 +1523,6 @@ xHalIoReadPartitionTable(IN PDEVICE_OBJECT DeviceObject,
         PartitionDescriptor = (PPARTITION_DESCRIPTOR)
                                &(((PUSHORT)Buffer)[PARTITION_TABLE_OFFSET]);
 
-        /* Get the partition type */
-        PartitionType = PartitionDescriptor->PartitionType;
-
         /* Start looping partitions */
         j++;
         DPRINT("FSTUB: Partition Table %d:\n", j);
@@ -1524,6 +1541,14 @@ xHalIoReadPartitionTable(IN PDEVICE_OBJECT DeviceObject,
                     GET_STARTING_SECTOR(PartitionDescriptor),
                     GET_PARTITION_LENGTH(PartitionDescriptor));
 
+            /* Check whether we're facing a protective MBR */
+            if (PartitionType == EFI_PMBR_OSTYPE_EFI)
+            {
+                /* Partition length might be bigger than disk size */
+                FstubFixupEfiPartition(PartitionDescriptor,
+                                       MaxOffset);
+            }
+
             /* Make sure that the partition is valid, unless it's the first */
             if (!(HalpIsValidPartitionEntry(PartitionDescriptor,
                                             MaxOffset,
-- 
2.17.1