[pschweitzer] 51002: [NTOSKRNL] Implemented FstubFixupEfiPartition(): Purpose is to let ReactOS handle realistic partitions length in case of an EFI/GPT protective MBR. Indeed, when formatting a di...

Author: pschweitzer
Date: Wed Mar  9 10:33:13 2011
New Revision: 51002

URL: http://svn.reactos.org/svn/reactos?rev=51002&view=rev
Log:
[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).

Modified:
    trunk/reactos/ntoskrnl/fstub/disksup.c

Modified: trunk/reactos/ntoskrnl/fstub/disksup.c
URL:
http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/fstub/disksup.c?r…
==============================================================================
--- trunk/reactos/ntoskrnl/fstub/disksup.c [iso-8859-1] (original)
+++ trunk/reactos/ntoskrnl/fstub/disksup.c [iso-8859-1] Wed Mar  9 10:33:13 2011
@@ -23,6 +23,8 @@
 #define AUTO_DRIVE         MAXULONG
 
 #define PARTITION_MAGIC    0xaa55
+
+#define EFI_PMBR_OSTYPE_EFI 0xEE
 
 #include <pshpack1.h>
 
@@ -1355,6 +1357,24 @@
                 ASSERT(PartitionDescriptor->PartitionType == 0x55);
             }
         }
+    }
+}
+
+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;
     }
 }
 
@@ -1425,7 +1445,7 @@
             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 @@
         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);
@@ -1523,6 +1540,14 @@
             DPRINT("\tOffset %#08lx for %#08lx Sectors\n",
                     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,