e83d841fdc
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>
99 lines
3.1 KiB
C
99 lines
3.1 KiB
C
/** @file
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Polymorphic functions that are called from both the privileged driver (i.e.,
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the DXE_SMM variable module) and the non-privileged drivers (i.e., one or
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both of the DXE_RUNTIME variable modules).
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Each of these functions has two implementations, appropriate for privileged
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vs. non-privileged driver code.
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Copyright (c) 2017, Red Hat, Inc.<BR>
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Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved.<BR>
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This program and the accompanying materials are licensed and made available
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under the terms and conditions of the BSD License which accompanies this
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distribution. The full text of the license may be found at
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http://opensource.org/licenses/bsd-license.php
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THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
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WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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**/
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#ifndef _PRIVILEGE_POLYMORPHIC_H_
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#define _PRIVILEGE_POLYMORPHIC_H_
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#include <Uefi/UefiBaseType.h>
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/**
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SecureBoot Hook for auth variable update.
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@param[in] VariableName Name of Variable to be found.
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@param[in] VendorGuid Variable vendor GUID.
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**/
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VOID
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EFIAPI
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SecureBootHook (
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IN CHAR16 *VariableName,
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IN EFI_GUID *VendorGuid
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);
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/**
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Initialization for MOR Control Lock.
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@retval EFI_SUCCESS MorLock initialization success.
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@return Others Some error occurs.
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**/
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EFI_STATUS
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MorLockInit (
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VOID
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);
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/**
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Delayed initialization for MOR Control Lock at EndOfDxe.
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This function performs any operations queued by MorLockInit().
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**/
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VOID
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MorLockInitAtEndOfDxe (
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VOID
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);
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/**
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This service is an MOR/MorLock checker handler for the SetVariable().
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@param[in] VariableName the name of the vendor's variable, as a
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Null-Terminated Unicode String
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@param[in] VendorGuid Unify identifier for vendor.
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@param[in] Attributes Attributes bitmask to set for the variable.
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@param[in] DataSize The size in bytes of Data-Buffer.
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@param[in] Data Point to the content of the variable.
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@retval EFI_SUCCESS The MOR/MorLock check pass, and Variable
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driver can store the variable data.
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@retval EFI_INVALID_PARAMETER The MOR/MorLock data or data size or
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attributes is not allowed for MOR variable.
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@retval EFI_ACCESS_DENIED The MOR/MorLock is locked.
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@retval EFI_ALREADY_STARTED The MorLock variable is handled inside this
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function. Variable driver can just return
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EFI_SUCCESS.
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**/
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EFI_STATUS
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SetVariableCheckHandlerMor (
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IN CHAR16 *VariableName,
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IN EFI_GUID *VendorGuid,
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IN UINT32 Attributes,
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IN UINTN DataSize,
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IN VOID *Data
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);
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/**
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This service is consumed by the variable modules to perform a serializing
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operation on all load-from-memory instructions that were issued prior to the
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call of this function.
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**/
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VOID
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MemoryLoadFence (
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VOID
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);
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#endif
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