|author||Hao Wu <email@example.com>||Thu Sep 13 15:53:31 2018 +0800|
|committer||Hao Wu <firstname.lastname@example.org>||Fri Nov 16 09:00:05 2018 +0800|
UefiCpuPkg/PiSmmCpuDxeSmm: [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. It is possible for SMI handler(s) to call EFI_SMM_CPU_PROTOCOL service ReadSaveState() and use the content in the 'CommBuffer' (controlled external inputs) as the 'CpuIndex'. So this commit will insert AsmLfence API to mitigate the bounds check bypass issue within SmmReadSaveState(). For SmmReadSaveState(): The 'CpuIndex' will be passed into function ReadSaveStateRegister(). And then in to ReadSaveStateRegisterByIndex(). With the call: ReadSaveStateRegisterByIndex ( CpuIndex, SMM_SAVE_STATE_REGISTER_IOMISC_INDEX, sizeof(IoMisc.Uint32), &IoMisc.Uint32 ); The 'IoMisc' can be a cross boundary access during speculative execution. Later, 'IoMisc' is used as the index to access buffers 'mSmmCpuIoWidth' and 'mSmmCpuIoType'. One can observe which part of the content within those buffers was brought into cache to possibly reveal the value of 'IoMisc'. Hence, this commit adds a AsmLfence() after the check of 'CpuIndex' within function SmmReadSaveState() 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: Michael D Kinney <email@example.com> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Hao Wu <firstname.lastname@example.org> Reviewed-by: Jiewen Yao <email@example.com> Reviewed-by: Eric Dong <firstname.lastname@example.org> Acked-by: Laszlo Ersek <email@example.com> Regression-tested-by: Laszlo Ersek <firstname.lastname@example.org> (cherry picked from commit 5b02be4d9a234d80c7578fc3a0c789d22ce83f38)
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