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IntelFrameworkModulePkg/IdeBusDxe: Fix undefined behavior in signed left shift 

In function AtapiReadCapacity(), the following expression:
IdeDev->BlkIo.Media->LastBlock = (Data.LastLba3 << 24) |
  (Data.LastLba2 << 16) |
  (Data.LastLba1 << 8) |
  Data.LastLba0;

(There is also a similar case in this function.)

will involve undefined behavior in signed left shift operations.

Since Data.LastLbaX is of type UINT8, and
IdeDev->BlkIo.Media->LastBlock is of type UINT64. Therefore,
Data.LastLbaX will be promoted to int (32 bits, signed) first,
and then perform the left shift operation.

According to the C11 spec, Section 6.5.7:
4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated
  bits are filled with zeros. If E1 has an unsigned type, the value
  of the result is E1 * 2^E2 , reduced modulo one more than the
  maximum value representable in the result type. If E1 has a signed
  type and nonnegative value, and E1 * 2^E2 is representable in the
  result type, then that is the resulting value; otherwise, the
  behavior is undefined.

So if bit 7 of Data.LastLba3 is 1, (Data.LastLba3 << 24) will be out of
the range within int type. The undefined behavior of the signed left shift
will lead to a potential of setting the high 32 bits of
IdeDev->BlkIo.Media->LastBlock to 1 during the cast from type int to type
UINT64.

This commit will add an explicit UINT32 type cast for Data.LastLba3 to
resolve this issue.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
This commit is contained in:
Hao Wu 2017-04-12 08:43:10 +08:00
parent a2617ed627
commit f90c4fff00
1 changed files with 3 additions and 3 deletions
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6
IntelFrameworkModulePkg/Bus/Pci/IdeBusDxe/Atapi.c
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@ -1,7 +1,7 @@
/** @file
This file contains all helper functions on the ATAPI command
Copyright (c) 2006 - 2010, 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
@ -1053,7 +1053,7 @@ AtapiReadCapacity (
if (!EFI_ERROR (Status) && *SResult == SenseNoSenseKey) {
if (IdeDev->Type == IdeCdRom) {
IdeDev->BlkIo.Media->LastBlock = (Data.LastLba3 << 24) |
IdeDev->BlkIo.Media->LastBlock = ((UINT32) Data.LastLba3 << 24) |
(Data.LastLba2 << 16) |
(Data.LastLba1 << 8) |
Data.LastLba0;
@ -1076,7 +1076,7 @@ AtapiReadCapacity (
IdeDev->BlkIo.Media->LastBlock = 0;
} else {
IdeDev->BlkIo.Media->LastBlock = (FormatData.LastLba3 << 24) |
IdeDev->BlkIo.Media->LastBlock = ((UINT32) FormatData.LastLba3 << 24) |
(FormatData.LastLba2 << 16) |
(FormatData.LastLba1 << 8) |
FormatData.LastLba0;