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From: Hao Wu <hao.a.wu@intel.com>
To: edk2-devel@lists.01.org
Cc: Hao Wu <hao.a.wu@intel.com>, Steven Shi <steven.shi@intel.com>,
	Eric Dong <eric.dong@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Michael Kinney <michael.d.kinney@intel.com>,
	Liming Gao <liming.gao@intel.com>
Subject: [PATCH v3 3/5] MdeModulePkg/Tpl: Fix negative value left shift
Date: Thu, 28 Sep 2017 12:32:11 +0800	[thread overview]
Message-ID: <20170928043213.20776-4-hao.a.wu@intel.com> (raw)
In-Reply-To: <20170928043213.20776-1-hao.a.wu@intel.com>

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=695

Within function CoreRestoreTpl(), left shift a negative value -2 is used
in:
"while (((-2 << NewTpl) & gEventPending) != 0) {"

which involves undefined behavior.

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 refines the code logic to avoid left shifting the negative
value.

Cc: Steven Shi <steven.shi@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Core/Dxe/Event/Tpl.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/Event/Tpl.c b/MdeModulePkg/Core/Dxe/Event/Tpl.c
index 8ad0a33701..e3caf832b8 100644
--- a/MdeModulePkg/Core/Dxe/Event/Tpl.c
+++ b/MdeModulePkg/Core/Dxe/Event/Tpl.c
@@ -1,7 +1,7 @@
 /** @file
   Task priority (TPL) functions.
 
-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
@@ -103,6 +103,7 @@ CoreRestoreTpl (
   )
 {
   EFI_TPL     OldTpl;
+  EFI_TPL     PendingTpl;
 
   OldTpl = gEfiCurrentTpl;
   if (NewTpl > OldTpl) {
@@ -123,8 +124,13 @@ CoreRestoreTpl (
   //
   // Dispatch any pending events
   //
-  while (((-2 << NewTpl) & gEventPending) != 0) {
-    gEfiCurrentTpl = (UINTN) HighBitSet64 (gEventPending);
+  while (gEventPending != 0) {
+    PendingTpl = (UINTN) HighBitSet64 (gEventPending);
+    if (PendingTpl <= NewTpl) {
+      break;
+    }
+
+    gEfiCurrentTpl = PendingTpl;
     if (gEfiCurrentTpl < TPL_HIGH_LEVEL) {
       CoreSetInterruptState (TRUE);
     }
-- 
2.12.0.windows.1



  parent reply	other threads:[~2017-09-28  4:29 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-28  4:32 [PATCH v3 0/5] Resolve undefined behaviours in left shift OPs Hao Wu
2017-09-28  4:32 ` [PATCH v3 1/5] MdePkg/PrintLib: Fix possible negative value left shift Hao Wu
2017-09-28  4:32 ` [PATCH v3 2/5] MdeModulePkg/PrintLib: " Hao Wu
2017-09-28  4:32 ` Hao Wu [this message]
2017-09-28  4:32 ` [PATCH v3 4/5] MdeModulePkg/DxeNetLib: Fix " Hao Wu
2017-09-28  5:42   ` Wu, Jiaxin
2017-09-28  7:21   ` Fu, Siyuan
2017-09-28  7:30   ` Ye, Ting
2017-09-28  4:32 ` [PATCH v3 5/5] MdeModulePkg/AtaAtapiPassThru: Fix possible out of range " Hao Wu
2017-09-28  5:12   ` Zeng, Star

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