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 FaultTolerantWriteDxe driver and insert LoadFence API to mitigate the bounds check bypass issue. For SMI handler SmmFaultTolerantWriteHandler(): Under "case FTW_FUNCTION_WRITE:", 'SmmFtwWriteHeader->Length' can be a potential cross boundary access of the 'CommBuffer' (controlled external inputs) during speculative execution. This cross boundary access is later passed as parameter 'Length' into function FtwWrite(). Within function FtwWrite(), the value of 'Length' can be inferred by code: "CopyMem (MyBuffer + Offset, Buffer, Length);". One can observe which part of the content within 'Buffer' was brought into cache to possibly reveal the value of 'Length'. Hence, this commit adds a LoadFence 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: Jiewen Yao <jiewen....@intel.com> Cc: Star Zeng <star.z...@intel.com> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Hao Wu <hao.a...@intel.com> --- MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.c | 2 ++ MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.inf | 1 + 2 files changed, 3 insertions(+) diff --git a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.c b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.c index 632313f076..2ed1bb9498 100644 --- a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.c +++ b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.c @@ -57,6 +57,7 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. #include <PiSmm.h> #include <Library/SmmServicesTableLib.h> #include <Library/SmmMemLib.h> +#include <Library/BaseLib.h> #include <Protocol/SmmSwapAddressRange.h> #include "FaultTolerantWrite.h" #include "FaultTolerantWriteSmmCommon.h" @@ -417,6 +418,7 @@ SmmFaultTolerantWriteHandler ( &SmmFvbHandle ); if (!EFI_ERROR (Status)) { + LoadFence (); Status = FtwWrite( &mFtwDevice->FtwInstance, SmmFtwWriteHeader->Lba, diff --git a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.inf b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.inf index 85d109e8d9..606cc2266b 100644 --- a/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.inf +++ b/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteSmm.inf @@ -55,6 +55,7 @@ PcdLib ReportStatusCodeLib SmmMemLib + BaseLib [Guids] # -- 2.12.0.windows.1 _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
