Re: [RFC PATCH 2/3] MdeModulePkg: Enable forward edge CFI in mem attributes table

["Michael D Kinney" <michael.d.kinney@intel.com>]

Hi Ard,

Since the PE/COFF image does not contain this information, is there an option
to add the information to an FFS file. Either as a new bit in a standard header
or as a GUIDed section defined by EDK II?

Since an FV may contain content build from source and additional content 
Integrated as binaries from other vendors, having a PCD that scopes this
attribute to all FVs many only work for FW builds that are 100% from sources.

Mike


> -----Original Message-----
> From: Ard Biesheuvel <ardb@kernel.org>
> Sent: Thursday, February 2, 2023 10:04 AM
> To: devel@edk2.groups.io
> Cc: Ard Biesheuvel <ardb@kernel.org>; Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <gaoliming@byosoft.com.cn>; Yao,
> Jiewen <jiewen.yao@intel.com>; Kubacki, Michael <michael.kubacki@microsoft.com>; Sean Brogan <sean.brogan@microsoft.com>; Rebecca
> Cran <quic_rcran@quicinc.com>; Leif Lindholm <quic_llindhol@quicinc.com>; Sami Mujawar <sami.mujawar@arm.com>; Taylor Beebe
> <t@taylorbeebe.com>
> Subject: [RFC PATCH 2/3] MdeModulePkg: Enable forward edge CFI in mem attributes table
> 
> The memory attributes table has been extended with a flag that indicates
> whether or not the OS is permitted to map the EFI runtime code regions
> with strict enforcement for IBT/BTI landing pad instructions.
> 
> This is generally a property of the firmware build, and so we can permit
> a platform to set this property using a PCD, and put the burden on the
> platform definition to set the toolchain options accordingly.
> 
> There is one snag, however: PE/COFF does not expose whether or not the
> code was generated with landing pads, so if any runtime DXE drivers were
> loaded from storage other than the firmware volumes, we must assume that
> setting the CFI flag in the memory attributes table is unsafe.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  MdeModulePkg/Core/Dxe/DxeMain.h                    |  2 ++
>  MdeModulePkg/Core/Dxe/DxeMain.inf                  |  1 +
>  MdeModulePkg/Core/Dxe/Image/Image.c                | 11 +++++++++++
>  MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c |  7 ++++++-
>  MdeModulePkg/MdeModulePkg.dec                      |  8 ++++++++
>  5 files changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/MdeModulePkg/Core/Dxe/DxeMain.h b/MdeModulePkg/Core/Dxe/DxeMain.h
> index 815a6b4bd844..427a5fc78f72 100644
> --- a/MdeModulePkg/Core/Dxe/DxeMain.h
> +++ b/MdeModulePkg/Core/Dxe/DxeMain.h
> @@ -280,6 +280,8 @@ extern EFI_MEMORY_TYPE_INFORMATION  gMemoryTypeInformation[EfiMaxMemoryType + 1]
>  extern BOOLEAN                    gDispatcherRunning;
> 
>  extern EFI_RUNTIME_ARCH_PROTOCOL  gRuntimeTemplate;
> 
> 
> 
> +extern BOOLEAN                    gMemoryAttributesTableForwardCfi;
> 
> +
> 
>  extern EFI_LOAD_FIXED_ADDRESS_CONFIGURATION_TABLE  gLoadModuleAtFixAddressConfigurationTable;
> 
>  extern BOOLEAN                                     gLoadFixedAddressCodeMemoryReady;
> 
>  //
> 
> diff --git a/MdeModulePkg/Core/Dxe/DxeMain.inf b/MdeModulePkg/Core/Dxe/DxeMain.inf
> index 35d5bf0dee6f..e6ff67773a69 100644
> --- a/MdeModulePkg/Core/Dxe/DxeMain.inf
> +++ b/MdeModulePkg/Core/Dxe/DxeMain.inf
> @@ -187,6 +187,7 @@ [Pcd]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPropertyMask                   ## CONSUMES
> 
>    gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard                           ## CONSUMES
> 
>    gEfiMdeModulePkgTokenSpaceGuid.PcdFwVolDxeMaxEncapsulationDepth           ## CONSUMES
> 
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdMemoryAttributesTableForwardCfi         ## CONSUMES
> 
> 
> 
>  # [Hob]
> 
>  # RESOURCE_DESCRIPTOR   ## CONSUMES
> 
> diff --git a/MdeModulePkg/Core/Dxe/Image/Image.c b/MdeModulePkg/Core/Dxe/Image/Image.c
> index 06cc6744b8c6..181fefdb6657 100644
> --- a/MdeModulePkg/Core/Dxe/Image/Image.c
> +++ b/MdeModulePkg/Core/Dxe/Image/Image.c
> @@ -1398,6 +1398,17 @@ CoreLoadImageCommon (
>      CoreNewDebugImageInfoEntry (EFI_DEBUG_IMAGE_INFO_TYPE_NORMAL, &Image->Info, Image->Handle);
> 
>    }
> 
> 
> 
> +  //
> 
> +  // If we loaded a runtime DXE driver from something other than a FV, it
> 
> +  // was not built as part of the firmware image, and so we cannot assume
> 
> +  // that it was built with IBT/BTI landing pads for forward edge control
> 
> +  // flow integrity.
> 
> +  //
> 
> +  if (!ImageIsFromFv &&
> 
> +      (Image->ImageContext.ImageCodeMemoryType == EfiRuntimeServicesCode)) {
> 
> +    gMemoryAttributesTableForwardCfi = FALSE;
> 
> +  }
> 
> +
> 
>    //
> 
>    // Reinstall loaded image protocol to fire any notifications
> 
>    //
> 
> diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c b/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c
> index e07921371187..cdd35ade0a8a 100644
> --- a/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c
> +++ b/MdeModulePkg/Core/Dxe/Misc/MemoryAttributesTable.c
> @@ -89,6 +89,7 @@ BOOLEAN                      mMemoryAttributesTableEnable      = TRUE;
>  BOOLEAN                      mMemoryAttributesTableEndOfDxe    = FALSE;
> 
>  EFI_MEMORY_ATTRIBUTES_TABLE  *mMemoryAttributesTable           = NULL;
> 
>  BOOLEAN                      mMemoryAttributesTableReadyToBoot = FALSE;
> 
> +BOOLEAN                      gMemoryAttributesTableForwardCfi  = FixedPcdGetBool (PcdMemoryAttributesTableForwardCfi);
> 
> 
> 
>  /**
> 
>    Install MemoryAttributesTable.
> 
> @@ -182,7 +183,11 @@ InstallMemoryAttributesTable (
>    MemoryAttributesTable->Version         = EFI_MEMORY_ATTRIBUTES_TABLE_VERSION;
> 
>    MemoryAttributesTable->NumberOfEntries = RuntimeEntryCount;
> 
>    MemoryAttributesTable->DescriptorSize  = (UINT32)DescriptorSize;
> 
> -  MemoryAttributesTable->Reserved        = 0;
> 
> +  if (gMemoryAttributesTableForwardCfi) {
> 
> +    MemoryAttributesTable->Flags         = EFI_MEMORY_ATTRIBUTES_FLAGS_RT_FORWARD_CONTROL_FLOW_GUARD;
> 
> +  } else {
> 
> +    MemoryAttributesTable->Flags         = 0;
> 
> +  }
> 
>    DEBUG ((DEBUG_VERBOSE, "MemoryAttributesTable:\n"));
> 
>    DEBUG ((DEBUG_VERBOSE, "  Version              - 0x%08x\n", MemoryAttributesTable->Version));
> 
>    DEBUG ((DEBUG_VERBOSE, "  NumberOfEntries      - 0x%08x\n", MemoryAttributesTable->NumberOfEntries));
> 
> diff --git a/MdeModulePkg/MdeModulePkg.dec b/MdeModulePkg/MdeModulePkg.dec
> index 9605c617b7a8..d336a38655a3 100644
> --- a/MdeModulePkg/MdeModulePkg.dec
> +++ b/MdeModulePkg/MdeModulePkg.dec
> @@ -1093,6 +1093,14 @@ [PcdsFixedAtBuild]
>    # @Prompt Enable UEFI Stack Guard.
> 
>    gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard|FALSE|BOOLEAN|0x30001055
> 
> 
> 
> +  ## Indicates whether the EFI memory attributes table will inform the OS that
> 
> +  #  forward edge control flow guards have been inserted into the runtime services
> 
> +  #  code regions.
> 
> +  #   TRUE  - Runtime code has forward control flow guards.<BR>
> 
> +  #   FALSE - Runtime code does not have forward control flow guards.<BR>
> 
> +  # @Prompt Enable forward control flow guards in EFI memory attributes table
> 
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdMemoryAttributesTableForwardCfi|FALSE|BOOLEAN|0x30001056
> 
> +
> 
>  [PcdsFixedAtBuild, PcdsPatchableInModule]
> 
>    ## Dynamic type PCD can be registered callback function for Pcd setting action.
> 
>    #  PcdMaxPeiPcdCallBackNumberPerPcdEntry indicates the maximum number of callback function
> 
> --
> 2.39.1