From a2617ed6277aeb62fbde3e428c582912cf9980e2 Mon Sep 17 00:00:00 2001 From: Hao Wu Date: Wed, 12 Apr 2017 09:06:36 +0800 Subject: [PATCH] MdeModulePkg/UsbBotPei: Fix undefined behavior in signed left shift In function PeiUsbReadCapacity(), the following expression: LastBlock = (Data.LastLba3 << 24) | (Data.LastLba2 << 16) | (Data.LastLba1 << 8) | Data.LastLba0; (There is also a similar case in function PeiUsbReadFormattedCapacity().) will involve undefined behavior in signed left shift operations. Since Data.LastLbaX is of type UINT8, they 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 might incur potential issues. This commit will add an explicit UINT32 type cast for Data.LastLba3 to refine the codes. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Hao Wu Reviewed-by: Feng Tian --- MdeModulePkg/Bus/Usb/UsbBotPei/PeiAtapi.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/MdeModulePkg/Bus/Usb/UsbBotPei/PeiAtapi.c b/MdeModulePkg/Bus/Usb/UsbBotPei/PeiAtapi.c index eaad626d61..72bde756eb 100644 --- a/MdeModulePkg/Bus/Usb/UsbBotPei/PeiAtapi.c +++ b/MdeModulePkg/Bus/Usb/UsbBotPei/PeiAtapi.c @@ -1,7 +1,7 @@ /** @file Pei USB ATATPI command implementations. -Copyright (c) 1999 - 2015, Intel Corporation. All rights reserved.
+Copyright (c) 1999 - 2017, Intel Corporation. All rights reserved.
This program and the accompanying materials are licensed and made available under the terms and conditions @@ -274,7 +274,7 @@ PeiUsbReadCapacity ( if (EFI_ERROR (Status)) { return EFI_DEVICE_ERROR; } - LastBlock = (Data.LastLba3 << 24) | (Data.LastLba2 << 16) | (Data.LastLba1 << 8) | Data.LastLba0; + LastBlock = ((UINT32) Data.LastLba3 << 24) | (Data.LastLba2 << 16) | (Data.LastLba1 << 8) | Data.LastLba0; if (LastBlock == 0xFFFFFFFF) { DEBUG ((EFI_D_INFO, "The usb device LBA count is larger than 0xFFFFFFFF!\n")); @@ -346,7 +346,7 @@ PeiUsbReadFormattedCapacity ( PeiBotDevice->Media2.LastBlock = 0; } else { - LastBlock = (FormatData.LastLba3 << 24) | (FormatData.LastLba2 << 16) | (FormatData.LastLba1 << 8) | FormatData.LastLba0; + LastBlock = ((UINT32) FormatData.LastLba3 << 24) | (FormatData.LastLba2 << 16) | (FormatData.LastLba1 << 8) | FormatData.LastLba0; if (LastBlock == 0xFFFFFFFF) { DEBUG ((EFI_D_INFO, "The usb device LBA count is larger than 0xFFFFFFFF!\n")); }