[PATCH v3 2/2] MdeModulePkg/RamDiskDxe: Restrict on RAM disk size (CVE-2018-12180)

[Hao Wu <hao.a.wu@intel.com>]

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1134

Originally, the block size of created Ram disks is hard-coded to 512
bytes. However, if the total size of the Ram disk is not a multiple of 512
bytes, there will be potential memory access issues when dealing with the
last block of the Ram disk.

This commit will adjust the block size of the Ram disks to ensure that the
total size is a multiple of the block size.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
---
 MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskImpl.h     |  6 +++---
 MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskBlockIo.c  | 20 ++++++++++++++------
 MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskProtocol.c |  5 +++--
 3 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskImpl.h b/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskImpl.h
index 08a8ca94c9..72f2bfe179 100644
--- a/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskImpl.h
+++ b/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskImpl.h
@@ -1,7 +1,7 @@
 /** @file
   The header file of RamDiskDxe driver.
 
-  Copyright (c) 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2016 - 2019, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
   which accompanies this distribution.  The full text of the license may be found at
@@ -49,9 +49,9 @@
 ///
 
 //
-// Block size for RAM disk
+// Default block size for RAM disk
 //
-#define RAM_DISK_BLOCK_SIZE 512
+#define RAM_DISK_DEFAULT_BLOCK_SIZE 512
 
 //
 // Iterate through the double linked list. NOT delete safe
diff --git a/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskBlockIo.c b/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskBlockIo.c
index 4f74b5ef15..8926ad7d2f 100644
--- a/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskBlockIo.c
+++ b/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskBlockIo.c
@@ -1,7 +1,7 @@
 /** @file
   Produce EFI_BLOCK_IO_PROTOCOL on a RAM disk device.
 
-  Copyright (c) 2016 - 2018, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2016 - 2019, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
   which accompanies this distribution.  The full text of the license may be found at
@@ -54,6 +54,7 @@ RamDiskInitBlockIo (
   EFI_BLOCK_IO_PROTOCOL           *BlockIo;
   EFI_BLOCK_IO2_PROTOCOL          *BlockIo2;
   EFI_BLOCK_IO_MEDIA              *Media;
+  UINT32                          Remainder;
 
   BlockIo  = &PrivateData->BlockIo;
   BlockIo2 = &PrivateData->BlockIo2;
@@ -69,11 +70,18 @@ RamDiskInitBlockIo (
   Media->LogicalPartition = FALSE;
   Media->ReadOnly         = FALSE;
   Media->WriteCaching     = FALSE;
-  Media->BlockSize        = RAM_DISK_BLOCK_SIZE;
-  Media->LastBlock        = DivU64x32 (
-                              PrivateData->Size + RAM_DISK_BLOCK_SIZE - 1,
-                              RAM_DISK_BLOCK_SIZE
-                              ) - 1;
+
+  for (Media->BlockSize = RAM_DISK_DEFAULT_BLOCK_SIZE;
+       Media->BlockSize >= 1;
+       Media->BlockSize = Media->BlockSize >> 1) {
+    Media->LastBlock = DivU64x32Remainder (PrivateData->Size, Media->BlockSize, &Remainder) - 1;
+    if (Remainder == 0) {
+      break;
+    }
+  }
+  ASSERT (Media->BlockSize != 0);
+
+  return;
 }
 
 
diff --git a/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskProtocol.c b/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskProtocol.c
index 6784e2b2f1..e8250d5c1b 100644
--- a/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskProtocol.c
+++ b/MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskProtocol.c
@@ -1,7 +1,7 @@
 /** @file
   The realization of EFI_RAM_DISK_PROTOCOL.
 
-  Copyright (c) 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2016 - 2019, Intel Corporation. All rights reserved.<BR>
   (C) Copyright 2016 Hewlett Packard Enterprise Development LP<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
@@ -613,7 +613,8 @@ RamDiskRegister (
   //
   // Add check to prevent data read across the memory boundary
   //
-  if (RamDiskBase + RamDiskSize > ((UINTN) -1) - RAM_DISK_BLOCK_SIZE + 1) {
+  if ((RamDiskSize > MAX_UINTN) ||
+      (RamDiskBase > MAX_UINTN - RamDiskSize + 1)) {
     return EFI_INVALID_PARAMETER;
   }
 
-- 
2.12.0.windows.1