Re: [PATCH v3 1/6] MdeModulePkg: Refine type cast for pointer subtraction

["Tian, Feng" <feng.tian@intel.com>]

Reviewed-by: Feng Tian <feng.tian@intel.com>

Thanks
Feng

-----Original Message-----
From: Wu, Hao A 
Sent: Saturday, February 25, 2017 12:05 PM
To: edk2-devel@lists.01.org
Cc: Wu, Hao A <hao.a.wu@intel.com>; Tian, Feng <feng.tian@intel.com>; Zeng, Star <star.zeng@intel.com>
Subject: [PATCH v3 1/6] MdeModulePkg: Refine type cast for pointer subtraction

For pointer subtraction, the result is of type "ptrdiff_t". According to the C11 standard (Committee Draft - April 12, 2011):

"When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. If the result is not representable in an object of that type, the behavior is undefined."

In our codes, there are cases that the pointer subtraction is not performed by pointers to elements of the same array object. This might lead to potential issues, since the behavior is undefined according to C11 standard.

Also, since the size of type "ptrdiff_t" is implementation-defined. Some static code checkers may warn that the pointer subtraction might underflow first and then being cast to a bigger size. For example:

UINT8  *Ptr1, *Ptr2;
UINTN  PtrDiff;
...
PtrDiff = (UINTN) (Ptr1 - Ptr2);

The commit will refine the pointer subtraction expressions by casting each pointer to UINTN first and then perform the subtraction:

PtrDiff = (UINTN) Ptr1 - (UINTN) Ptr2;

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciOptionRomSupport.c              |  4 ++--
 MdeModulePkg/Include/Library/NetLib.h                             |  6 +++---
 MdeModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c             |  4 ++--
 MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c         |  2 +-
 MdeModulePkg/Library/FileExplorerLib/FileExplorer.c               |  4 ++--
 MdeModulePkg/Library/PiDxeS3BootScriptLib/BootScriptSave.c        |  4 ++--
 MdeModulePkg/Library/UefiBootManagerLib/BmLoadOption.c            |  4 ++--
 MdeModulePkg/Universal/DebugPortDxe/DebugPort.c                   |  4 ++--
 MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c |  4 ++--
 MdeModulePkg/Universal/HiiDatabaseDxe/Image.c                     |  4 ++--
 MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c             | 10 +++++-----
 11 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciOptionRomSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciOptionRomSupport.c
index 2bc4f8c..d2ad94e 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciOptionRomSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciOptionRomSupport.c
@@ -1,7 +1,7 @@
 /** @file
   PCI Rom supporting funtions implementation for PCI Bus module.
 
-Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, 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 @@ -776,7 +776,7 @@ ProcessOpRomImage (
 NextImage:
     RomBarOffset += ImageSize;
 
-  } while (((Indicator & 0x80) == 0x00) && ((UINTN) (RomBarOffset - (UINT8 *) RomBar) < PciDevice->RomSize));
+  } while (((Indicator & 0x80) == 0x00) && (((UINTN) RomBarOffset - 
+ (UINTN) RomBar) < PciDevice->RomSize));
 
   return RetStatus;
 }
diff --git a/MdeModulePkg/Include/Library/NetLib.h b/MdeModulePkg/Include/Library/NetLib.h
index 09ead09..3b8ff1a 100644
--- a/MdeModulePkg/Include/Library/NetLib.h
+++ b/MdeModulePkg/Include/Library/NetLib.h
@@ -2,7 +2,7 @@
   This library is only intended to be used by UEFI network stack modules.
   It provides basic functions for the UEFI network stack.
 
-Copyright (c) 2005 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2005 - 2017, 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<BR> @@ -1610,10 +1610,10 @@ typedef struct {
   (sizeof (NET_BUF) + ((BlockOpNum) - 1) * sizeof (NET_BLOCK_OP))
 
 #define NET_HEADSPACE(BlockOp)  \
-  (UINTN)((BlockOp)->Head - (BlockOp)->BlockHead)
+  ((UINTN)((BlockOp)->Head) - (UINTN)((BlockOp)->BlockHead))
 
 #define NET_TAILSPACE(BlockOp)  \
-  (UINTN)((BlockOp)->BlockTail - (BlockOp)->Tail)
+  ((UINTN)((BlockOp)->BlockTail) - (UINTN)((BlockOp)->Tail))
 
 /**
   Allocate a single block NET_BUF. Upon allocation, all the diff --git a/MdeModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c b/MdeModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c
index 71e05bd..d7abcc8 100644
--- a/MdeModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c
+++ b/MdeModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c
@@ -10,7 +10,7 @@
   ValidateFmpCapsule(), DisplayCapsuleImage(), ConvertBmpToGopBlt() will
   receive untrusted input and do basic validation.
 
-  Copyright (c) 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2016 - 2017, 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 @@ -547,7 +547,7 @@ ConvertBmpToGopBlt (
 
     }
 
-    ImageIndex = (UINTN) (Image - ImageHeader);
+    ImageIndex = (UINTN) Image - (UINTN) ImageHeader;
     if ((ImageIndex % 4) != 0) {
       //
       // Bmp Image starts each row on a 32-bit boundary!
diff --git a/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c b/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c
index 589d4db..d9aeb92 100644
--- a/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c
+++ b/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c
@@ -226,7 +226,7 @@ DxePrintLibPrint2ProtocolVaListToBaseList (
     //
     // If BASE_LIST is larger than Size, then return FALSE
     //
-    if ((UINTN)((UINT8 *)BaseListMarker - (UINT8 *)BaseListStart) > Size) {
+    if (((UINTN)BaseListMarker - (UINTN)BaseListStart) > Size) {
       DEBUG ((DEBUG_ERROR, "The input variable argument list is too long. Please consider breaking into multiple print calls.\n"));
       return FALSE;
     }
diff --git a/MdeModulePkg/Library/FileExplorerLib/FileExplorer.c b/MdeModulePkg/Library/FileExplorerLib/FileExplorer.c
index 5eedad7..9182751 100644
--- a/MdeModulePkg/Library/FileExplorerLib/FileExplorer.c
+++ b/MdeModulePkg/Library/FileExplorerLib/FileExplorer.c
@@ -728,7 +728,7 @@ LibAppendFileName (
       // that overlap.
       //
       StrCpyS (TmpStr, MaxLen, Ptr + 3);
-      StrCpyS (LastSlash, MaxLen - (UINTN) (LastSlash - Str), TmpStr);
+      StrCpyS (LastSlash, MaxLen - ((UINTN) LastSlash - (UINTN) Str) / 
+ sizeof (CHAR16), TmpStr);
       Ptr = LastSlash;
     } else if (*Ptr == '\\' && *(Ptr + 1) == '.' && *(Ptr + 2) == '\\') {
       //
@@ -740,7 +740,7 @@ LibAppendFileName (
       // that overlap.
       //
       StrCpyS (TmpStr, MaxLen, Ptr + 2);
-      StrCpyS (Ptr, MaxLen - (UINTN) (Ptr - Str), TmpStr);
+      StrCpyS (Ptr, MaxLen - ((UINTN) Ptr - (UINTN) Str) / sizeof 
+ (CHAR16), TmpStr);
       Ptr = LastSlash;
     } else if (*Ptr == '\\') {
       LastSlash = Ptr;
diff --git a/MdeModulePkg/Library/PiDxeS3BootScriptLib/BootScriptSave.c b/MdeModulePkg/Library/PiDxeS3BootScriptLib/BootScriptSave.c
index 5698c91..1f8aaf4 100644
--- a/MdeModulePkg/Library/PiDxeS3BootScriptLib/BootScriptSave.c
+++ b/MdeModulePkg/Library/PiDxeS3BootScriptLib/BootScriptSave.c
@@ -1,7 +1,7 @@
 /** @file
   Save the S3 data to S3 boot script.
 
-  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 2017, Intel Corporation. All rights 
+ reserved.<BR>
 
   This program and the accompanying materials
   are licensed and made available under the terms and conditions @@ -2025,7 +2025,7 @@ S3BootScriptCalculateInsertAddress (
    // calculate the Position offset
    //
    if (Position != NULL) {
-     PositionOffset = (UINTN) ((UINT8 *)Position - S3TableBase);
+     PositionOffset = (UINTN)Position - (UINTN)S3TableBase;
 
      //
      // If the BeforeOrAfter is FALSE, that means to insert the node right after the node.
diff --git a/MdeModulePkg/Library/UefiBootManagerLib/BmLoadOption.c b/MdeModulePkg/Library/UefiBootManagerLib/BmLoadOption.c
index 6f705bd..116cf28 100644
--- a/MdeModulePkg/Library/UefiBootManagerLib/BmLoadOption.c
+++ b/MdeModulePkg/Library/UefiBootManagerLib/BmLoadOption.c
@@ -1,7 +1,7 @@
 /** @file
   Load option library functions which relate with creating and processing load options.
 
-Copyright (c) 2011 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2011 - 2017, Intel Corporation. All rights reserved.<BR>
 (C) Copyright 2015-2016 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 @@ -912,7 +912,7 @@ EfiBootManagerVariableToLoadOptionEx (
   FilePath = (EFI_DEVICE_PATH_PROTOCOL *) VariablePtr;
   VariablePtr += FilePathSize;
 
-  OptionalDataSize = (UINT32) (VariableSize - (UINTN) (VariablePtr - Variable));
+  OptionalDataSize = (UINT32) (VariableSize - ((UINTN) VariablePtr - 
+ (UINTN) Variable));
   if (OptionalDataSize == 0) {
     OptionalData = NULL;
   } else {
diff --git a/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c b/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c
index 298b6b2..dcb623c 100644
--- a/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c
+++ b/MdeModulePkg/Universal/DebugPortDxe/DebugPort.c
@@ -4,7 +4,7 @@
   ALL CODE IN THE SERIALIO STACK MUST BE RE-ENTRANT AND CALLABLE FROM
   INTERRUPT CONTEXT
 
-Copyright (c) 2006 - 2014, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, 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 @@ -569,7 +569,7 @@ DebugPortRead (
     LocalBufferSize = *BufferSize - (BufferPtr - (UINT8 *) Buffer);
   } while (LocalBufferSize != 0 && Timeout > 0);
 
-  *BufferSize = (UINTN) (BufferPtr - (UINT8 *) Buffer);
+  *BufferSize = (UINTN) BufferPtr - (UINTN) Buffer;
 
   return Status;
 }
diff --git a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c
index 2e3e8c7..49e747b 100644
--- a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c
+++ b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWrite.c
@@ -3,7 +3,7 @@
   These are the common Fault Tolerant Write (FTW) functions that are shared 
   by DXE FTW driver and SMM FTW driver.
 
-Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, 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        
@@ -373,7 +373,7 @@ FtwWrite (
   //
   // If Record is out of the range of Header, return access denied.
   //
-  if (((UINTN)((UINT8 *) Record - (UINT8 *) Header)) > FTW_WRITE_TOTAL_SIZE (Header->NumberOfWrites - 1, Header->PrivateDataSize)) {
+  if (((UINTN) Record - (UINTN) Header) > FTW_WRITE_TOTAL_SIZE 
+ (Header->NumberOfWrites - 1, Header->PrivateDataSize)) {
     return EFI_ACCESS_DENIED;
   }
 
diff --git a/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c b/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c
index 1668828..e2fa16e 100644
--- a/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c
+++ b/MdeModulePkg/Universal/HiiDatabaseDxe/Image.c
@@ -2,7 +2,7 @@
 Implementation for EFI_HII_IMAGE_PROTOCOL.
 
 
-Copyright (c) 2007 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2007 - 2017, 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 @@ -1124,7 +1124,7 @@ HiiSetImage (
     return EFI_OUT_OF_RESOURCES;
   }
 
-  Part1Size = (UINT32) (UINTN) ((UINT8 *) CurrentImageBlock - (UINT8 *) ImagePackage->ImageBlock);
+  Part1Size = (UINT32) ((UINTN) CurrentImageBlock - (UINTN) 
+ ImagePackage->ImageBlock);
   Part2Size = ImagePackage->ImageBlockSize - Part1Size - OldBlockSize;
   CopyMem (ImageBlocks, ImagePackage->ImageBlock, Part1Size);
 
diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
index f5b6a5f..b0c7434 100644
--- a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
+++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
@@ -16,7 +16,7 @@
   VariableServiceSetVariable() should also check authenticate data to avoid buffer overflow,
   integer overflow. It should also check attribute to avoid authentication bypass.
 
-Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
 (C) Copyright 2015 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 @@ -1170,7 +1170,7 @@ Reclaim (
   // Install the new variable if it is not NULL.
   //
   if (NewVariable != NULL) {
-    if ((UINTN) (CurrPtr - ValidBuffer) + NewVariableSize > VariableStoreHeader->Size) {
+    if (((UINTN) CurrPtr - (UINTN) ValidBuffer) + NewVariableSize > 
+ VariableStoreHeader->Size) {
       //
       // No enough space to store the new variable.
       //
@@ -1211,8 +1211,8 @@ Reclaim (
     // If volatile variable store, just copy valid buffer.
     //
     SetMem ((UINT8 *) (UINTN) VariableBase, VariableStoreHeader->Size, 0xff);
-    CopyMem ((UINT8 *) (UINTN) VariableBase, ValidBuffer, (UINTN) (CurrPtr - ValidBuffer));
-    *LastVariableOffset = (UINTN) (CurrPtr - ValidBuffer);
+    CopyMem ((UINT8 *) (UINTN) VariableBase, ValidBuffer, (UINTN) CurrPtr - (UINTN) ValidBuffer);
+    *LastVariableOffset = (UINTN) CurrPtr - (UINTN) ValidBuffer;
     Status  = EFI_SUCCESS;
   } else {
     //
@@ -1223,7 +1223,7 @@ Reclaim (
               (VARIABLE_STORE_HEADER *) ValidBuffer
               );
     if (!EFI_ERROR (Status)) {
-      *LastVariableOffset = (UINTN) (CurrPtr - ValidBuffer);
+      *LastVariableOffset = (UINTN) CurrPtr - (UINTN) ValidBuffer;
       mVariableModuleGlobal->HwErrVariableTotalSize = HwErrVariableTotalSize;
       mVariableModuleGlobal->CommonVariableTotalSize = CommonVariableTotalSize;
       mVariableModuleGlobal->CommonUserVariableTotalSize = CommonUserVariableTotalSize;
--
1.9.5.msysgit.0