Re: [PATCH v1 1/5] MdePkg/BaseLib: Add new LoadFence API

[Laszlo Ersek <lersek@redhat.com>]

On 09/20/18 08:40, Hao Wu wrote:
> REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1193
> 
> This commit will add a new BaseLib API LoadFence(). This API will perform
> a serializing operation on all load-from-memory instructions that were
> issued prior to the call of this function.
> 
> The purpose of adding this API is to mitigate of the [CVE-2017-5753]
> Bounds Check Bypass issue when untrusted data are being processed within
> SMM. More details can be referred at the 'Bounds check bypass mitigation'
> section at the below link:
> 
> https://software.intel.com/security-software-guidance/insights/host-firmware-speculative-execution-side-channel-mitigation
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Hao Wu <hao.a.wu@intel.com>
> ---
>  MdePkg/Include/Library/BaseLib.h           | 12 +++++++
>  MdePkg/Library/BaseLib/Arm/LoadFence.c     | 26 ++++++++++++++
>  MdePkg/Library/BaseLib/BaseLib.inf         |  4 +++
>  MdePkg/Library/BaseLib/Ebc/CpuBreakpoint.c | 15 +++++++-
>  MdePkg/Library/BaseLib/Ia32/LoadFence.nasm | 37 +++++++++++++++++++
>  MdePkg/Library/BaseLib/X64/LoadFence.nasm  | 38 ++++++++++++++++++++
>  6 files changed, 131 insertions(+), 1 deletion(-)
> 
> diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
> index 123ae19dc2..194726ca35 100644
> --- a/MdePkg/Include/Library/BaseLib.h
> +++ b/MdePkg/Include/Library/BaseLib.h
> @@ -4939,6 +4939,18 @@ MemoryFence (
>  
>  
>  /**
> +  Performs a serializing operation on all load-from-memory instructions that
> +  were issued prior to the call of this function.
> +
> +**/
> +VOID
> +EFIAPI
> +LoadFence (
> +  VOID
> +  );
> +
> +
> +/**
>    Saves the current CPU context that can be restored with a call to LongJump()
>    and returns 0.
>  
> diff --git a/MdePkg/Library/BaseLib/Arm/LoadFence.c b/MdePkg/Library/BaseLib/Arm/LoadFence.c
> new file mode 100644
> index 0000000000..69f0c3a07e
> --- /dev/null
> +++ b/MdePkg/Library/BaseLib/Arm/LoadFence.c
> @@ -0,0 +1,26 @@
> +/** @file
> +  LoadFence() function for ARM.
> +
> +  Copyright (C) 2018, Intel Corporation. All rights reserved.<BR>
> +
> +  This program and the accompanying materials are licensed and made available
> +  under the terms and conditions of the BSD License which accompanies this
> +  distribution.  The full text of the license may be found at
> +  http://opensource.org/licenses/bsd-license.php.
> +
> +  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
> +  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
> +**/
> +
> +/**
> +  Performs a serializing operation on all load-from-memory instructions that
> +  were issued prior to the call of this function.
> +
> +**/
> +VOID
> +EFIAPI
> +LoadFence (
> +  VOID
> +  )
> +{
> +}
> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf b/MdePkg/Library/BaseLib/BaseLib.inf
> index a1b5ec4b75..f028fbc75a 100644
> --- a/MdePkg/Library/BaseLib/BaseLib.inf
> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
> @@ -68,6 +68,7 @@
>  
>  [Sources.Ia32]
>    Ia32/WriteTr.nasm
> +  Ia32/LoadFence.nasm
>  
>    Ia32/Wbinvd.c | MSFT
>    Ia32/WriteMm7.c | MSFT
> @@ -346,6 +347,7 @@
>    X64/EnableCache.nasm
>    X64/DisableCache.nasm
>    X64/WriteTr.nasm
> +  X64/LoadFence.nasm
>  
>    X64/CpuBreakpoint.c | MSFT
>    X64/WriteMsr64.c | MSFT
> @@ -580,6 +582,7 @@
>  [Sources.ARM]
>    Arm/InternalSwitchStack.c
>    Arm/Unaligned.c
> +  Arm/LoadFence.c
>    Math64.c                   | RVCT
>    Math64.c                   | MSFT
>  
> @@ -613,6 +616,7 @@
>  [Sources.AARCH64]
>    Arm/InternalSwitchStack.c
>    Arm/Unaligned.c
> +  Arm/LoadFence.c
>    Math64.c
>  
>    AArch64/MemoryFence.S             | GCC
> diff --git a/MdePkg/Library/BaseLib/Ebc/CpuBreakpoint.c b/MdePkg/Library/BaseLib/Ebc/CpuBreakpoint.c
> index 9b7d875664..a79461cfbf 100644
> --- a/MdePkg/Library/BaseLib/Ebc/CpuBreakpoint.c
> +++ b/MdePkg/Library/BaseLib/Ebc/CpuBreakpoint.c
> @@ -1,7 +1,7 @@
>  /** @file
>    Base Library CPU Functions for EBC
>  
> -  Copyright (c) 2006 - 2010, Intel Corporation. All rights reserved.<BR>
> +  Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
>    This program and the accompanying materials
>    are licensed and made available under the terms and conditions of the BSD License
>    which accompanies this distribution.  The full text of the license may be found at
> @@ -52,6 +52,19 @@ MemoryFence (
>  }
>  
>  /**
> +  Performs a serializing operation on all load-from-memory instructions that
> +  were issued prior to the call of this function.
> +
> +**/
> +VOID
> +EFIAPI
> +LoadFence (
> +  VOID
> +  )
> +{
> +}
> +
> +/**
>    Disables CPU interrupts.
>  
>  **/
> diff --git a/MdePkg/Library/BaseLib/Ia32/LoadFence.nasm b/MdePkg/Library/BaseLib/Ia32/LoadFence.nasm
> new file mode 100644
> index 0000000000..11600bea76
> --- /dev/null
> +++ b/MdePkg/Library/BaseLib/Ia32/LoadFence.nasm
> @@ -0,0 +1,37 @@
> +;------------------------------------------------------------------------------ ;
> +; Copyright (c) 2018, Intel Corporation. All rights reserved.<BR>
> +; This program and the accompanying materials
> +; are licensed and made available under the terms and conditions of the BSD License
> +; which accompanies this distribution.  The full text of the license may be found at
> +; http://opensource.org/licenses/bsd-license.php.
> +;
> +; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
> +; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
> +;
> +; Module Name:
> +;
> +;   LoadFence.nasm
> +;
> +; Abstract:
> +;
> +;   Performs a serializing operation on all load-from-memory instructions that
> +;   were issued prior to the call of this function.
> +;
> +; Notes:
> +;
> +;------------------------------------------------------------------------------
> +
> +    SECTION .text
> +
> +;------------------------------------------------------------------------------
> +; VOID
> +; EFIAPI
> +; LoadFence (
> +;   VOID
> +;   );
> +;------------------------------------------------------------------------------
> +global ASM_PFX(LoadFence)
> +ASM_PFX(LoadFence):
> +    lfence
> +    ret
> +
> diff --git a/MdePkg/Library/BaseLib/X64/LoadFence.nasm b/MdePkg/Library/BaseLib/X64/LoadFence.nasm
> new file mode 100644
> index 0000000000..c076d9789d
> --- /dev/null
> +++ b/MdePkg/Library/BaseLib/X64/LoadFence.nasm
> @@ -0,0 +1,38 @@
> +;------------------------------------------------------------------------------ ;
> +; Copyright (c) 2018, Intel Corporation. All rights reserved.<BR>
> +; This program and the accompanying materials
> +; are licensed and made available under the terms and conditions of the BSD License
> +; which accompanies this distribution.  The full text of the license may be found at
> +; http://opensource.org/licenses/bsd-license.php.
> +;
> +; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
> +; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
> +;
> +; Module Name:
> +;
> +;   LoadFence.nasm
> +;
> +; Abstract:
> +;
> +;   Performs a serializing operation on all load-from-memory instructions that
> +;   were issued prior to the call of this function.
> +;
> +; Notes:
> +;
> +;------------------------------------------------------------------------------
> +
> +    DEFAULT REL
> +    SECTION .text
> +
> +;------------------------------------------------------------------------------
> +; VOID
> +; EFIAPI
> +; LoadFence (
> +;   VOID
> +;   );
> +;------------------------------------------------------------------------------
> +global ASM_PFX(LoadFence)
> +ASM_PFX(LoadFence):
> +    lfence
> +    ret
> +
> 

Comments in no particular order:

(1) I think the EBC stub implementation should go into a separate file
under "MdePkg/Library/BaseLib/Ebc".

(2) Given that the ARM memory model is laxer than x86, I'm doubtful that
an empty implementation is appropriate. I expect a DMB variant should be
used, but I totally defer to Ard and Leif on that.

(3) We have Arm/ and AArch64/ subdirectories, but only one common
variant is provided, under Arm/. (I expect this fact (i.e., "common
variant") might remain true even after considering (2).) What I find
inconsistent though is that Ia32 and X64 get separate NASM files,
despite them sharing the implementation between each other as well.

IOW, this remark isn't about the actual implementation of the new API;
it's about consistency. If we decide for one ISA that the 32-bit and
64-bit platforms use a common set of files, then the other ISA (also
with 32-bit and 64-bit platforms) should act similarly, if a common
implementation is possible.

Thanks
Laszlo