Please ignore this one. Some more information need to be added in the subject line. Another patch mail has been sent out to address this.
Best Regards, Hao Wu > -----Original Message----- > From: edk2-devel [mailto:[email protected]] On Behalf Of Hao > Wu > Sent: Sunday, September 30, 2018 1:26 PM > To: [email protected] > Cc: Wu, Hao A; Yao, Jiewen > Subject: [edk2] [PATCH v1] MinPlatformPkg/Test: [CVE-2017-5753] Fix bounds > check bypass > > 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 > TestPointCheckLib & TestPointLib and insert AsmLfence API to mitigate the > bounds check bypass issue. > > A. For SMI handler TestPointSmmHandler() within TestPointCheckLib: > > Under "case > TEST_POINT_SMM_COMMUNICATION_FUNC_ID_UEFI_GCD_MAP_INFO:", > 'CommBuffer' (controlled external inputs) is passed into function > TestPointSmmReadyToBootSmmPageProtectionHandler(). > > Within function TestPointSmmReadyToBootSmmPageProtectionHandler(), the > contents in 'CommBuffer' will be copied into 'CommData'. But if the size > and sanity checks for the communication buffer is speculatively bypassed, > '(UINTN)CommData + CommData->UefiMemoryMapOffset)' can potentially > point > to cross boundary area of 'CommData'. This pointer is then passed into > function TestPointCheckSmmCommunicationBuffer() as 'UefiMemoryMap'. > > Within function TestPointCheckSmmCommunicationBuffer(), > 'MemoryMap->PhysicalStart' can be a potential cross boundary access. And > its value can be inferred by function calls sequence: > > TestPointCheckPageTable() via 'BaseAddress' > GetPageTableEntry() via 'BaseAddress'. Then one can observe which part of > the content within arrays 'L4PageTable', 'L3PageTable', 'L2PageTable' or > 'L1PageTable', was brought into cache to possibly reveal the value. > > B. For SMI handler SmmTestPointSmiHandler() within TestPointLib: > > Under "case > SMI_HANDLER_TEST_POINT_COMMAND_GET_DATA_BY_OFFSET:", > 'CommBuffer' (controlled external inputs) is passed into function > SmmTestPointSmiHandlerGetDataByOffset(). > > Within function SmmTestPointSmiHandlerGetDataByOffset(), the contents in > 'CommBuffer' will be copied into 'SmiHandlerTestPointGetDataByOffset'. But > if the size and sanity checks for the communication buffer is > speculatively bypassed, 'SmiHandlerTestPointGetDataByOffset.DataSize' can > be a potential cross boundary access. > > Then in function SmiHandlerTestPointCopyData(), this value can be inferred > by code: > CopyMem( > DataBuffer, > (UINT8 *)InputData + *DataOffset, > (UINTN)*DataSize > ); > One can observe which part of the content within 'DataBuffer' was brought > into cache to possibly reveal the cross bounary access value. > > Hence, this commit adds AsmLfence() calls after the boundary/range checks > of the communication buffer 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 <[email protected]> > Contributed-under: TianoCore Contribution Agreement 1.1 > Signed-off-by: Hao Wu <[email protected]> > --- > > Platform/Intel/MinPlatformPkg/Test/Library/TestPointCheckLib/SmmTestPoint > CheckLib.c | 7 +++++++ > > Platform/Intel/MinPlatformPkg/Test/Library/TestPointLib/SmmTestPointComm > unication.c | 8 +++++++- > 2 files changed, 14 insertions(+), 1 deletion(-) > > diff --git > a/Platform/Intel/MinPlatformPkg/Test/Library/TestPointCheckLib/SmmTestPoi > ntCheckLib.c > b/Platform/Intel/MinPlatformPkg/Test/Library/TestPointCheckLib/SmmTestPoi > ntCheckLib.c > index b40469b278..dc40dae6d5 100644 > --- > a/Platform/Intel/MinPlatformPkg/Test/Library/TestPointCheckLib/SmmTestPoi > ntCheckLib.c > +++ > b/Platform/Intel/MinPlatformPkg/Test/Library/TestPointCheckLib/SmmTestPoi > ntCheckLib.c > @@ -14,6 +14,7 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY > KIND, EITHER EXPRESS OR IMPLIED. > #include <PiSmm.h> > #include <Library/TestPointCheckLib.h> > #include <Library/TestPointLib.h> > +#include <Library/BaseLib.h> > #include <Library/DebugLib.h> > #include <Library/BaseMemoryLib.h> > #include <Library/MemoryAllocationLib.h> > @@ -374,6 +375,12 @@ > TestPointSmmReadyToBootSmmPageProtectionHandler ( > } > > if (CommData->UefiMemoryMapSize != 0) { > + // > + // The AsmLfence() call here is to ensure the previous range/content > checks > + // for the CommBuffer (copied in to CommData) have been completed > before > + // calling into TestPointCheckSmmCommunicationBuffer(). > + // > + AsmLfence (); > Result = TRUE; > > Status = TestPointCheckSmmCommunicationBuffer ( > diff --git > a/Platform/Intel/MinPlatformPkg/Test/Library/TestPointLib/SmmTestPointCom > munication.c > b/Platform/Intel/MinPlatformPkg/Test/Library/TestPointLib/SmmTestPointCom > munication.c > index cce0538832..b4757da046 100644 > --- > a/Platform/Intel/MinPlatformPkg/Test/Library/TestPointLib/SmmTestPointCom > munication.c > +++ > b/Platform/Intel/MinPlatformPkg/Test/Library/TestPointLib/SmmTestPointCom > munication.c > @@ -251,7 +251,13 @@ SmmTestPointSmiHandlerGetDataByOffset ( > SmiHandlerTestPointParameterGetDataByOffset->Header.ReturnStatus = > (UINT64)(INT64)(INTN)Status; > goto Done; > } > - > + > + // > + // The AsmLfence() call here is to ensure the previous range/content checks > + // for the CommBuffer have been completed before calling into > + // SmiHandlerTestPointCopyData(). > + // > + AsmLfence (); > SmiHandlerTestPointCopyData ( > Data, > DataSize, > -- > 2.12.0.windows.1 > > _______________________________________________ > edk2-devel mailing list > [email protected] > https://lists.01.org/mailman/listinfo/edk2-devel _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
