[PARTMGR] Detect and flag partitionless ("super-floppy") disks (#6926)

CORE-15575

Detect whether the disk is a "super-floppy", which is the name given
to partitionless disk having no MBR, with the unique partition volume
starting at sector offset zero and spanning the whole disk.
The name comes from the fact that at the partitioning level, the disk
"looks like" a large-capacity floppy disk.

This is typically how external removable (USB, ...) drives are
partitioned by default by Windows.

https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-and-gpt-faq?view=windows-11#superfloppy

The kernel-mode functions IoReadPartitionTable() / IoWritePartitionTable()
report the drive layout of a "super-floppy" disk as follows:
an MBR-style disk containing only one single partition starting at the
beginning of the disk (StartingOffset == 0) without hidden sectors, and
its type being FAT16 non-bootable.
The disk NTFT signature is set to 0x00000001.

----

Additional bug fixes to make the feature work reliably:

- Make PartMgrGetDriveLayout() also update the FDO DiskData's
  PartitionStyle and Signature/GPT DiskId for consistency (code moved
  from PartMgrRefreshDiskData()).

- In FdoIoctlDiskSetDriveLayout[Ex](), if the disk is "super-floppy",
  but the user wants to create more than one partition, fail the call.
  (In the Ex call, fail also if the partition style changes.)

drivers/storage/partmgr/partmgr.c

@@ -114,6 +114,84 @@ PartMgrConvertLayoutToExtended(
     return layoutEx;
 }
 
+/**
+ * @brief
+ * Detects whether a disk is a "super-floppy", i.e. an unpartitioned
+ * disk with only a valid VBR, as reported by IoReadPartitionTable()
+ * and IoWritePartitionTable():
+ * only one single partition starting at offset zero and spanning the
+ * whole disk, without hidden sectors, whose type is FAT16 non-bootable.
+ *
+ * Accessing \Device\HarddiskN\Partition0 or Partition1 on such disks
+ * returns the same data.
+ *
+ * @note
+ * - Requires partitioning lock held.
+ * - Uses the cached disk partition layout.
+ **/
+static
+CODE_SEG("PAGE")
+BOOLEAN
+PartMgrIsDiskSuperFloppy(
+    _In_ PFDO_EXTENSION FdoExtension)
+{
+    PPARTITION_INFORMATION_EX PartitionInfo;
+
+    PAGED_CODE();
+
+    ASSERT(FdoExtension->LayoutValid && FdoExtension->LayoutCache);
+
+    /* We must be MBR and have only one partition */
+    ASSERT(FdoExtension->DiskData.PartitionStyle == FdoExtension->LayoutCache->PartitionStyle);
+    if (FdoExtension->DiskData.PartitionStyle != PARTITION_STYLE_MBR)
+        return FALSE;
+    if (FdoExtension->LayoutCache->PartitionCount != 1)
+        return FALSE;
+
+    /* Get the single partition entry */
+    PartitionInfo = FdoExtension->LayoutCache->PartitionEntry;
+    ASSERT(FdoExtension->DiskData.PartitionStyle == PartitionInfo->PartitionStyle);
+
+    /* The single partition must start at the beginning of the disk */
+    if (!(PartitionInfo->StartingOffset.QuadPart == 0 &&
+          PartitionInfo->Mbr.HiddenSectors == 0))
+    {
+        return FALSE;
+    }
+
+    /* The disk signature is usually set to 1; warn in case it's not */
+    ASSERT(FdoExtension->DiskData.Mbr.Signature == FdoExtension->LayoutCache->Mbr.Signature);
+    if (FdoExtension->DiskData.Mbr.Signature != 1)
+    {
+        WARN("Super-Floppy disk %lu signature %08x != 1!\n",
+             FdoExtension->DiskData.DeviceNumber, FdoExtension->DiskData.Mbr.Signature);
+    }
+
+    /* The partition must be recognized and report as FAT16 non-bootable */
+    if ((PartitionInfo->Mbr.RecognizedPartition != TRUE) ||
+        (PartitionInfo->Mbr.PartitionType != PARTITION_FAT_16) ||
+        (PartitionInfo->Mbr.BootIndicator != FALSE))
+    {
+        WARN("Super-Floppy disk %lu does not return default settings!\n"
+             "    RecognizedPartition = %s, expected TRUE\n"
+             "    PartitionType = 0x%02x, expected 0x04 (PARTITION_FAT_16)\n"
+             "    BootIndicator = %s, expected FALSE\n",
+             FdoExtension->DiskData.DeviceNumber,
+             PartitionInfo->Mbr.RecognizedPartition ? "TRUE" : "FALSE",
+             PartitionInfo->Mbr.PartitionType,
+             PartitionInfo->Mbr.BootIndicator ? "TRUE" : "FALSE");
+    }
+
+    /* The partition and disk sizes should agree */
+    if (PartitionInfo->PartitionLength.QuadPart != FdoExtension->DiskData.DiskSize)
+    {
+        WARN("PartitionLength = %I64u is different from DiskSize = %I64u\n",
+             PartitionInfo->PartitionLength.QuadPart, FdoExtension->DiskData.DiskSize);
+    }
+
+    return TRUE;
+}
+
 static
 CODE_SEG("PAGE")
 VOID
@@ -304,7 +382,7 @@ PartMgrUpdatePartitionDevices(
         }
         else
         {
-            // insert in the beginning
+            // insert at the beginning
             partExt->ListEntry.Next = FdoExtension->PartitionList.Next;
             FdoExtension->PartitionList.Next = &partExt->ListEntry;
         }
@@ -315,7 +393,15 @@ PartMgrUpdatePartitionDevices(
     FdoExtension->EnumeratedPartitionsTotal = totalPartitions;
 }
 
-// requires partitioning lock held
+/**
+ * @brief
+ * Retrieves the disk partition layout from the given disk FDO.
+ *
+ * If the disk layout cache is valid, just return it; otherwise,
+ * read the partition table layout from disk and update the cache.
+ *
+ * @note    Requires partitioning lock held.
+ **/
 static
 CODE_SEG("PAGE")
 NTSTATUS
@@ -333,22 +419,29 @@ PartMgrGetDriveLayout(
 
     PDRIVE_LAYOUT_INFORMATION_EX layoutEx = NULL;
     NTSTATUS status = IoReadPartitionTableEx(FdoExtension->LowerDevice, &layoutEx);
-
     if (!NT_SUCCESS(status))
-    {
         return status;
-    }
 
     if (FdoExtension->LayoutCache)
-    {
         ExFreePool(FdoExtension->LayoutCache);
-    }
 
     FdoExtension->LayoutCache = layoutEx;
     FdoExtension->LayoutValid = TRUE;
 
-    *DriveLayout = layoutEx;
+    FdoExtension->DiskData.PartitionStyle = layoutEx->PartitionStyle;
+    if (FdoExtension->DiskData.PartitionStyle == PARTITION_STYLE_MBR)
+    {
+        FdoExtension->DiskData.Mbr.Signature = layoutEx->Mbr.Signature;
+        // FdoExtension->DiskData.Mbr.Checksum = geometryEx.Partition.Mbr.CheckSum;
+    }
+    else
+    {
+        FdoExtension->DiskData.Gpt.DiskId = layoutEx->Gpt.DiskId;
+    }
 
+    FdoExtension->IsSuperFloppy = PartMgrIsDiskSuperFloppy(FdoExtension);
+
+    *DriveLayout = layoutEx;
     return status;
 }
 
@@ -493,7 +586,6 @@ FdoIoctlDiskGetDriveLayout(
 
     PDRIVE_LAYOUT_INFORMATION_EX layoutEx;
     NTSTATUS status = PartMgrGetDriveLayout(FdoExtension, &layoutEx);
-
     if (!NT_SUCCESS(status))
     {
         PartMgrReleaseLayoutLock(FdoExtension);
@@ -603,6 +695,14 @@ FdoIoctlDiskSetDriveLayout(
 
     PartMgrAcquireLayoutLock(FdoExtension);
 
+    // If the current disk is super-floppy but the user changes
+    // the number of partitions to > 1, fail the call.
+    if (FdoExtension->IsSuperFloppy && (layoutEx->PartitionCount > 1))
+    {
+        PartMgrReleaseLayoutLock(FdoExtension);
+        return STATUS_INVALID_DEVICE_REQUEST;
+    }
+
     // this in fact updates the bus relations
     PartMgrUpdatePartitionDevices(FdoExtension, layoutEx);
 
@@ -625,6 +725,8 @@ FdoIoctlDiskSetDriveLayout(
 
             part->PartitionNumber = layoutEx->PartitionEntry[i].PartitionNumber;
         }
+
+        FdoExtension->IsSuperFloppy = PartMgrIsDiskSuperFloppy(FdoExtension);
     }
     else
     {
@@ -690,6 +792,16 @@ FdoIoctlDiskSetDriveLayoutEx(
 
     PartMgrAcquireLayoutLock(FdoExtension);
 
+    // If the current disk is super-floppy but the user changes either
+    // the disk type or the number of partitions to > 1, fail the call.
+    if (FdoExtension->IsSuperFloppy &&
+        ((layoutEx->PartitionStyle != PARTITION_STYLE_MBR) ||
+         (layoutEx->PartitionCount > 1)))
+    {
+        PartMgrReleaseLayoutLock(FdoExtension);
+        return STATUS_INVALID_DEVICE_REQUEST;
+    }
+
     // if partition count is 0, it's the same as IOCTL_DISK_CREATE_DISK
     if (layoutEx->PartitionCount == 0)
     {
@@ -734,6 +846,8 @@ FdoIoctlDiskSetDriveLayoutEx(
         }
         FdoExtension->LayoutCache = layoutEx;
         FdoExtension->LayoutValid = TRUE;
+
+        FdoExtension->IsSuperFloppy = PartMgrIsDiskSuperFloppy(FdoExtension);
     }
     else
     {
@@ -879,7 +993,13 @@ FdoHandleStartDevice(
     return status;
 }
 
-// requires partitioning lock held
+/**
+ * @brief
+ * Refreshes all the cached disk FDO data.
+ * The geometry of the disk and its partition layout cache is updated.
+ *
+ * @note    Requires partitioning lock held.
+ **/
 static
 CODE_SEG("PAGE")
 NTSTATUS
@@ -900,9 +1020,7 @@ PartMgrRefreshDiskData(
                                        sizeof(geometryEx),
                                        FALSE);
     if (!NT_SUCCESS(status))
-    {
         return status;
-    }
 
     FdoExtension->DiskData.DiskSize = geometryEx.DiskSize.QuadPart;
     FdoExtension->DiskData.BytesPerSector = geometryEx.Geometry.BytesPerSector;
@@ -911,20 +1029,7 @@ PartMgrRefreshDiskData(
     PDRIVE_LAYOUT_INFORMATION_EX layoutEx = NULL;
     status = PartMgrGetDriveLayout(FdoExtension, &layoutEx);
     if (!NT_SUCCESS(status))
-    {
         return status;
-    }
-
-    FdoExtension->DiskData.PartitionStyle = layoutEx->PartitionStyle;
-    if (FdoExtension->DiskData.PartitionStyle == PARTITION_STYLE_MBR)
-    {
-        FdoExtension->DiskData.Mbr.Signature = layoutEx->Mbr.Signature;
-        // FdoExtension->DiskData.Mbr.Checksum = geometryEx.Partition.Mbr.CheckSum;
-    }
-    else
-    {
-        FdoExtension->DiskData.Gpt.DiskId = layoutEx->Gpt.DiskId;
-    }
 
     return STATUS_SUCCESS;
 }
@@ -957,8 +1062,8 @@ FdoHandleDeviceRelations(
 
         INFO("Partition style %u\n", FdoExtension->DiskData.PartitionStyle);
 
-        // PartMgrAcquireLayoutLock calls PartMgrGetDriveLayout inside
+        // PartMgrRefreshDiskData() calls PartMgrGetDriveLayout() inside
-        // so we're sure here that it returns only cached layout
+        // so we're sure here that it returns only the cached layout.
         PDRIVE_LAYOUT_INFORMATION_EX layoutEx;
         PartMgrGetDriveLayout(FdoExtension, &layoutEx);
 

drivers/storage/partmgr/partmgr.h

@@ -44,7 +44,7 @@ typedef struct _FDO_EXTENSION
 
     SINGLE_LIST_ENTRY PartitionList;
     UINT32 EnumeratedPartitionsTotal;
-    UNICODE_STRING DiskInterfaceName;
+    BOOLEAN IsSuperFloppy;
 
     struct {
         UINT64 DiskSize;
@@ -60,6 +60,7 @@ typedef struct _FDO_EXTENSION
             } Gpt;
         };
     } DiskData;
+    UNICODE_STRING DiskInterfaceName;
 } FDO_EXTENSION, *PFDO_EXTENSION;
 
 typedef struct _PARTITION_EXTENSION