REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1194
Speculative execution is used by processor to avoid having to wait for data to arrive from memory, or for previous operations to finish, the processor may speculate as to what will be executed. If the speculation is incorrect, the speculatively executed instructions might leave hints such as which memory locations have been brought into cache. Malicious actors can use the bounds check bypass method (code gadgets with controlled external inputs) to infer data values that have been used in speculative operations to reveal secrets which should not otherwise be accessed. This commit will focus on the SMI handler(s) registered within the OpalPasswordSupportLib and insert AsmLfence API to mitigate the bounds check bypass issue. For SMI handler SmmOpalPasswordHandler(): Under "case SMM_FUNCTION_SET_OPAL_PASSWORD:", '&DeviceBuffer->OpalDevicePath' can points to a potential cross boundary access of the 'CommBuffer' (controlled external inputs) during speculative execution. This cross boundary access pointer is later passed as parameter 'DevicePath' into function OpalSavePasswordToSmm(). Within function OpalSavePasswordToSmm(), 'DevicePathLen' is an access to the content in 'DevicePath' and can be inferred by code: "CompareMem (&List->OpalDevicePath, DevicePath, DevicePathLen)". One can observe which part of the content within either '&List->OpalDevicePath' or 'DevicePath' was brought into cache to possibly reveal the value of 'DevicePathLen'. Hence, this commit adds a AsmLfence() after the boundary/range checks of 'CommBuffer' to prevent the speculative execution. A more detailed explanation of the purpose of commit is under the 'Bounds check bypass mitigation' section of the below link: https://software.intel.com/security-software-guidance/insights/host-firmware-speculative-execution-side-channel-mitigation And the document at: https://software.intel.com/security-software-guidance/api-app/sites/default/files/337879-analyzing-potential-bounds-Check-bypass-vulnerabilities.pdf Cc: Star Zeng <[email protected]> Cc: Chao Zhang <[email protected]> Cc: Jiewen Yao <[email protected]> Cc: Laszlo Ersek <[email protected]> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Hao Wu <[email protected]> --- SecurityPkg/Library/OpalPasswordSupportLib/OpalPasswordSupportLib.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/SecurityPkg/Library/OpalPasswordSupportLib/OpalPasswordSupportLib.c b/SecurityPkg/Library/OpalPasswordSupportLib/OpalPasswordSupportLib.c index e377e9ca79..1c3bfffb86 100644 --- a/SecurityPkg/Library/OpalPasswordSupportLib/OpalPasswordSupportLib.c +++ b/SecurityPkg/Library/OpalPasswordSupportLib/OpalPasswordSupportLib.c @@ -1,7 +1,7 @@ /** @file Implementation of Opal password support library. -Copyright (c) 2016, Intel Corporation. All rights reserved.<BR> +Copyright (c) 2016 - 2018, 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 @@ -706,6 +706,11 @@ SmmOpalPasswordHandler ( Status = EFI_INVALID_PARAMETER; goto EXIT; } + // + // The AsmLfence() call here is to ensure the above range checks for the + // CommBuffer have been completed before calling into OpalSavePasswordToSmm(). + // + AsmLfence (); Status = OpalSavePasswordToSmm (&DeviceBuffer->OpalDevicePath, DeviceBuffer->Password, DeviceBuffer->PasswordLength); break; -- 2.12.0.windows.1 _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
