Re: [PATCH v2 6/6] MdeModulePkg/AtaAtapiPassThru: Fix possible out of range left shift

["Zeng, Star" <star.zeng@intel.com>]

I prefer to have the code consistent between this patch with [PATCH v2 5/6] MdeModulePkg/Crc32: Fix possible out of range left shift.

Both to use (UINT32) typecast or 1U.

Liming, Do you have any comment?


Thanks,
Star
-----Original Message-----
From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Hao Wu
Sent: Thursday, September 21, 2017 2:46 PM
To: edk2-devel@lists.01.org
Cc: Wu, Hao A <hao.a.wu@intel.com>; Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
Subject: [edk2] [PATCH v2 6/6] MdeModulePkg/AtaAtapiPassThru: Fix possible out of range left shift

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=699

Within function AhciModeInitialization(), left shift operations of 'BIT0'
in the following statements:
"if ((PortImplementBitMap & (BIT0 << Port)) != 0) {"

will incur possible out of range left shift when Port is 31, since
"1 << 31" is possible to exceed the range of type 'int' (signed).

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.

This commit explicitly cast 'BIT0' with UINT32 to resolve this issue.

Cc: Steven Shi <steven.shi@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
---
 MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AhciMode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AhciMode.c b/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AhciMode.c
index b954de8101..e6de5d65bc 100644
--- a/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AhciMode.c
+++ b/MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AhciMode.c
@@ -1,7 +1,7 @@
 /** @file
   The file for AHCI mode of ATA host controller.
 
-  Copyright (c) 2010 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2010 - 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 @@ -2314,7 +2314,7 @@ AhciModeInitialization (
   }
 
   for (Port = 0; Port < EFI_AHCI_MAX_PORTS; Port ++) {
-    if ((PortImplementBitMap & (BIT0 << Port)) != 0) {
+    if ((PortImplementBitMap & (((UINT32)BIT0) << Port)) != 0) {
       //
       // According to AHCI spec, MaxPortNumber should be equal or greater than the number of implemented ports.
       //
--
2.12.0.windows.1

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