From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 87DFD20D7648C for ; Tue, 11 Apr 2017 18:52:35 -0700 (PDT) Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Apr 2017 18:52:35 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.37,187,1488873600"; d="scan'208";a="1134232238" Received: from shwdeopenpsi014.ccr.corp.intel.com ([10.239.9.13]) by fmsmga001.fm.intel.com with ESMTP; 11 Apr 2017 18:52:34 -0700 From: Hao Wu To: edk2-devel@lists.01.org, guoheyi@huawei.com Cc: Hao Wu , Feng Tian Date: Wed, 12 Apr 2017 09:52:25 +0800 Message-Id: <20170412015228.20328-3-hao.a.wu@intel.com> X-Mailer: git-send-email 2.12.0.windows.1 In-Reply-To: <20170412015228.20328-1-hao.a.wu@intel.com> References: <20170412015228.20328-1-hao.a.wu@intel.com> Subject: [PATCH v3 2/5] MdeModulePkg/IdeBusPei: Fix undefined behavior in signed left shift X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 12 Apr 2017 01:52:35 -0000 In function ReadCapacity(), the following expression: MediaInfo->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 MediaInfo->LastBlock is of type UINTN. 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 MediaInfo->LastBlock to 1 during the cast from type int to type UINT64 for X64 builds. This commit will add an explicit UINT32 type cast for Data.LastLba3 to resolve this issue. Cc: Feng Tian Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Hao Wu --- MdeModulePkg/Bus/Pci/IdeBusPei/AtapiPeim.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/MdeModulePkg/Bus/Pci/IdeBusPei/AtapiPeim.c b/MdeModulePkg/Bus/Pci/IdeBusPei/AtapiPeim.c index b1ab34d597..58bef161fb 100644 --- a/MdeModulePkg/Bus/Pci/IdeBusPei/AtapiPeim.c +++ b/MdeModulePkg/Bus/Pci/IdeBusPei/AtapiPeim.c @@ -2140,7 +2140,7 @@ ReadCapacity ( if (MediaInfo->DeviceType == IdeCDROM) { - MediaInfo->LastBlock = (Data.LastLba3 << 24) | (Data.LastLba2 << 16) | (Data.LastLba1 << 8) | Data.LastLba0; + MediaInfo->LastBlock = ((UINT32) Data.LastLba3 << 24) | (Data.LastLba2 << 16) | (Data.LastLba1 << 8) | Data.LastLba0; MediaInfo->MediaPresent = TRUE; // // Because the user data portion in the sector of the Data CD supported @@ -2161,7 +2161,7 @@ ReadCapacity ( MediaInfo2->MediaPresent = FALSE; MediaInfo2->LastBlock = 0; } else { - MediaInfo->LastBlock = (FormatData.LastLba3 << 24) | + MediaInfo->LastBlock = ((UINT32) FormatData.LastLba3 << 24) | (FormatData.LastLba2 << 16) | (FormatData.LastLba1 << 8) | FormatData.LastLba0; -- 2.12.0.windows.1