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system76-edk2/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf
Hao Wu e83d841fdc MdeModulePkg/Variable: [CVE-2017-5753] Fix bounds check bypass 
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
Variable\RuntimeDxe driver and insert AsmLfence API to mitigate the
bounds check bypass issue.

For SMI handler SmmVariableHandler():

Under "case SMM_VARIABLE_FUNCTION_GET_VARIABLE:",
'SmmVariableHeader->NameSize' can be a potential cross boundary access of
the 'CommBuffer' (controlled external input) during speculative execution.

This cross boundary access is later used as the index to access array
'SmmVariableHeader->Name' by code:
"SmmVariableHeader->Name[SmmVariableHeader->NameSize/sizeof (CHAR16) - 1]"
One can observe which part of the content within array was brought into
cache to possibly reveal the value of 'SmmVariableHeader->NameSize'.

Hence, this commit adds a AsmLfence() after the boundary/range checks of
'CommBuffer' to prevent the speculative execution.

And there are 2 similar cases under
"case SMM_VARIABLE_FUNCTION_SET_VARIABLE:" and
"case SMM_VARIABLE_FUNCTION_VAR_CHECK_VARIABLE_PROPERTY_GET:" as well.
This commits also handles them.

Also, under "case SMM_VARIABLE_FUNCTION_SET_VARIABLE:",
'(UINT8 *)SmmVariableHeader->Name + SmmVariableHeader->NameSize' points to
the 'CommBuffer' (with some offset) and then passed as parameter 'Data' to
function VariableServiceSetVariable().

Within function VariableServiceSetVariable(), there is a sanity check for
EFI_VARIABLE_AUTHENTICATION_2 descriptor for the data pointed by 'Data'.
If this check is speculatively bypassed, potential cross-boundary data
access for 'Data' is possible to be revealed via the below function calls
sequence during speculative execution:

AuthVariableLibProcessVariable()
ProcessVarWithPk() or ProcessVarWithKek()

Within function ProcessVarWithPk() or ProcessVarWithKek(), for the code
"PayloadSize = DataSize - AUTHINFO2_SIZE (Data);", 'AUTHINFO2_SIZE (Data)'
can be a cross boundary access during speculative execution.

Then, 'PayloadSize' is possible to be revealed by the function call
sequence:

AuthServiceInternalUpdateVariableWithTimeStamp()
mAuthVarLibContextIn->UpdateVariable()
VariableExLibUpdateVariable()
UpdateVariable()
CopyMem()

Hence, this commit adds a AsmLfence() after the sanity check for
EFI_VARIABLE_AUTHENTICATION_2 descriptor upon 'Data' within function
VariableServiceSetVariable() to prevent the speculative execution.

Also, please note that the change made within function
VariableServiceSetVariable() will affect DXE as well. However, since we
only focuses on the SMM codes, the commit will introduce a new module
internal function called VariableLoadFence() to handle this. This internal
function will have 2 implementations (1 for SMM, 1 for DXE). For the SMM
implementation, it is a wrapper to call the AsmLfence() API; for the DXE
implementation, it is empty.

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: Jiewen Yao <jiewen.yao@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>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
2018-09-30 13:06:42 +08:00

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## @file
# Provides variable service.
#
# This module installs variable arch protocol and variable write arch protocol to provide
# variable services: SetVariable, GetVariable, GetNextVariableName and QueryVariableInfo.
#
# Caution: This module requires additional review when modified.
# This driver will have external input - variable data.
# This external input must be validated carefully to avoid security issues such as
# buffer overflow or integer overflow.
#
# 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
# http://opensource.org/licenses/bsd-license.php
# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
# WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
#
##
[Defines]
INF_VERSION = 0x00010005
BASE_NAME = VariableRuntimeDxe
MODULE_UNI_FILE = VariableRuntimeDxe.uni
FILE_GUID = CBD2E4D5-7068-4FF5-B462-9822B4AD8D60
MODULE_TYPE = DXE_RUNTIME_DRIVER
VERSION_STRING = 1.0
ENTRY_POINT = VariableServiceInitialize
#
# The following information is for reference only and not required by the build tools.
#
# VALID_ARCHITECTURES = IA32 X64 EBC
#
# VIRTUAL_ADDRESS_MAP_CALLBACK = VariableClassAddressChangeEvent
#
[Sources]
Reclaim.c
Variable.c
VariableDxe.c
Variable.h
PrivilegePolymorphic.h
Measurement.c
TcgMorLockDxe.c
VarCheck.c
VariableExLib.c
LoadFenceDxe.c
[Packages]
MdePkg/MdePkg.dec
MdeModulePkg/MdeModulePkg.dec
[LibraryClasses]
MemoryAllocationLib
BaseLib
SynchronizationLib
UefiLib
UefiBootServicesTableLib
BaseMemoryLib
DebugLib
UefiRuntimeLib
DxeServicesTableLib
UefiDriverEntryPoint
PcdLib
HobLib
TpmMeasurementLib
AuthVariableLib
VarCheckLib
[Protocols]
gEfiFirmwareVolumeBlockProtocolGuid ## CONSUMES
## CONSUMES
## NOTIFY
gEfiFaultTolerantWriteProtocolGuid
gEfiVariableWriteArchProtocolGuid ## PRODUCES
gEfiVariableArchProtocolGuid ## PRODUCES
gEdkiiVariableLockProtocolGuid ## PRODUCES
gEdkiiVarCheckProtocolGuid ## PRODUCES
[Guids]
## SOMETIMES_CONSUMES ## GUID # Signature of Variable store header
## SOMETIMES_PRODUCES ## GUID # Signature of Variable store header
## SOMETIMES_CONSUMES ## HOB
## SOMETIMES_PRODUCES ## SystemTable
gEfiAuthenticatedVariableGuid
## SOMETIMES_CONSUMES ## GUID # Signature of Variable store header
## SOMETIMES_PRODUCES ## GUID # Signature of Variable store header
## SOMETIMES_CONSUMES ## HOB
## SOMETIMES_PRODUCES ## SystemTable
gEfiVariableGuid
## SOMETIMES_CONSUMES ## Variable:L"PlatformLang"
## SOMETIMES_PRODUCES ## Variable:L"PlatformLang"
## SOMETIMES_CONSUMES ## Variable:L"Lang"
## SOMETIMES_PRODUCES ## Variable:L"Lang"
## SOMETIMES_CONSUMES ## Variable:L"PK"
## SOMETIMES_CONSUMES ## Variable:L"KEK"
## SOMETIMES_CONSUMES ## Variable:L"SecureBoot"
gEfiGlobalVariableGuid
gEfiMemoryOverwriteControlDataGuid ## SOMETIMES_CONSUMES ## Variable:L"MemoryOverwriteRequestControl"
gEfiMemoryOverwriteRequestControlLockGuid ## SOMETIMES_PRODUCES ## Variable:L"MemoryOverwriteRequestControlLock"
gEfiEventVirtualAddressChangeGuid ## CONSUMES ## Event
gEfiSystemNvDataFvGuid ## CONSUMES ## GUID
gEfiEndOfDxeEventGroupGuid ## CONSUMES ## Event
gEdkiiFaultTolerantWriteGuid ## SOMETIMES_CONSUMES ## HOB
## SOMETIMES_CONSUMES ## Variable:L"VarErrorFlag"
## SOMETIMES_PRODUCES ## Variable:L"VarErrorFlag"
gEdkiiVarErrorFlagGuid
## SOMETIMES_CONSUMES ## Variable:L"db"
## SOMETIMES_CONSUMES ## Variable:L"dbx"
## SOMETIMES_CONSUMES ## Variable:L"dbt"
gEfiImageSecurityDatabaseGuid
[Pcd]
gEfiMdeModulePkgTokenSpaceGuid.PcdFlashNvStorageVariableSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdFlashNvStorageVariableBase ## SOMETIMES_CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdFlashNvStorageVariableBase64 ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVolatileVariableSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdMaxHardwareErrorVariableSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdVariableStoreSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdHwErrStorageSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdMaxUserNvVariableSpaceSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdBoottimeReservedNvVariableSpaceSize ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdReclaimVariableSpaceAtEndOfDxe ## CONSUMES
[FeaturePcd]
gEfiMdeModulePkgTokenSpaceGuid.PcdVariableCollectStatistics ## CONSUMES # statistic the information of variable.
gEfiMdePkgTokenSpaceGuid.PcdUefiVariableDefaultLangDeprecate ## CONSUMES # Auto update PlatformLang/Lang
[Depex]
TRUE
[UserExtensions.TianoCore."ExtraFiles"]
VariableRuntimeDxeExtra.uni
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