mirror of https://github.com/acidanthera/audk.git
4 Commits
| Author | SHA1 | Message | Date |
|---|---|---|---|
Hao Wu
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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> |
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Laszlo Ersek
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f130428043 |
MdeModulePkg/Variable/RuntimeDxe: introduce MorLockInitAtEndOfDxe() hook
Introduce the MorLockInitAtEndOfDxe() hook, in order to allow MorLockInit() to delay / queue operations until EndOfDxe. (Or, if the platform never signals EndOfDxe, until ReadyToBoot.) Call MorLockInitAtEndOfDxe() whenever we set "mEndOfDxe" to TRUE: - in VariableRuntimeDxe: - in the OnReadyToBoot() function, - in the OnEndOfDxe() function; - in VariableSmm: - on the SMM_VARIABLE_FUNCTION_READY_TO_BOOT SMI request, - in the SmmEndOfDxeCallback() function. For now, implement MorLockInitAtEndOfDxe() as a no-op in both VariableRuntimeDxe and VariableSmm. Cc: Eric Dong <eric.dong@intel.com> Cc: Jiewen Yao <jiewen.yao@intel.com> Cc: Ladi Prosek <lprosek@redhat.com> Cc: Star Zeng <star.zeng@intel.com> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Jiewen Yao <jiewen.yao@intel.com> Tested-by: Ladi Prosek <lprosek@redhat.com> |
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Laszlo Ersek
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03877377e3 |
MdeModulePkg/Variable/RuntimeDxe: move MOR func. declarations to header
The MorLockInit() and SetVariableCheckHandlerMor() functions have separate
implementations for VariableRuntimeDxe (= unprivileged, unified
DXE_RUNTIME driver) and VariableSmm (= privileged, DXE_SMM back-end of the
split variable driver).
Move their declarations from "Variable.c" to "PrivilegePolymorphic.h", so
that the compiler enforce that the declarations and the definitions match.
(All C source files with the call sites and the function definitions
already include "PrivilegePolymorphic.h" via "Variable.h".)
At the same time:
- replace two typos in the MorLockInit() description:
- replace "EFI_SUCEESS" with "EFI_SUCCESS",
- replace "MOR Lock Control" with "MOR Control Lock";
- in the SetVariableCheckHandlerMor() description:
- replace @param with @param[in],
- correct the description of the Attributes parameter (suggested by Star
Zeng <star.zeng@intel.com>),
- rewrap the comment to 80 columns.
This change cleans up commit
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Laszlo Ersek
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00663d047f |
MdeModulePkg/Variable/RuntimeDxe: move SecureBootHook() decl to new header
If the platform supports SMM, a gRT->SetVariable() call at boot time
results in the following call tree to SecureBootHook():
RuntimeServiceSetVariable() [VariableSmmRuntimeDxe.c, unprivileged]
SmmVariableHandler() [VariableSmm.c, PRIVILEGED]
VariableServiceSetVariable() [Variable.c, PRIVILEGED]
SecureBootHook() [VariableSmm.c, PRIVILEGED]
//
// do nothing
//
SecureBootHook() [Measurement.c, unprivileged]
//
// measure variable if it
// is related to SB policy
//
And if the platform does not support SMM:
VariableServiceSetVariable() [Variable.c, unprivileged]
SecureBootHook() [Measurement.c, unprivileged]
//
// measure variable if it
// is related to SB policy
//
In other words, the measurement always happens outside of SMM.
Because there are two implementations of the SecureBootHook() API, one
that is called from SMM and does nothing, and another that is called
outside of SMM and measures variables, the function declaration should be
in a header file. This way the compiler can enforce that the function
declaration and all function definitions match.
"Variable.h" is used for "including common header files, defining internal
structures and functions used by Variable modules". Technically, we could
declare SecureBootHook() in "Variable.h". However, "Measurement.c" and
"VariableSmmRuntimeDxe.c" themselves do not include "Variable.h", and that
is likely intentional -- "Variable.h" exposes so much of the privileged
variable implementation that it is likely excluded from these C source
files on purpose.
Therefore introduce a new header file called "PrivilegePolymorphic.h".
"Variable.h" includes this header (so that all C source files that have
been allowed to see the variable internals learn about the new
SecureBootHook() declaration immediately). In "Measurement.c" and
"VariableSmmRuntimeDxe.c", include *only* the new header.
This change cleans up commit
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