Re: [edk2-devel] [PATCH v3 1/4] StandaloneMmPkg/Core: Limit FwVol encapsulation section recursion

["Laszlo Ersek" <lersek@redhat.com>]

On 10/30/23 08:49, Wei6 Xu wrote:
> MmCoreFfsFindMmDriver() is called recursively for encapsulation sections.
> Currently this recursion is not limited. Introduce a new PCD
> (fixed-at-build, or patchable-in-module), and make MmCoreFfsFindMmDriver()
> track the section nesting depth against that PCD.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Sami Mujawar <sami.mujawar@arm.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Signed-off-by: Wei6 Xu <wei6.xu@intel.com>
> ---
>  StandaloneMmPkg/Core/FwVol.c              | 16 ++++++++++++++--
>  StandaloneMmPkg/Core/StandaloneMmCore.c   |  5 +++--
>  StandaloneMmPkg/Core/StandaloneMmCore.inf |  3 +++
>  StandaloneMmPkg/StandaloneMmPkg.dec       |  5 +++++
>  4 files changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/StandaloneMmPkg/Core/FwVol.c b/StandaloneMmPkg/Core/FwVol.c
> index 1f6d7714ba97..e1e20ffd14ac 100644
> --- a/StandaloneMmPkg/Core/FwVol.c
> +++ b/StandaloneMmPkg/Core/FwVol.c
> @@ -48,6 +48,9 @@ FvIsBeingProcessed (
>    MM driver and return its PE32 image.
>  
>    @param [in] FwVolHeader   Pointer to memory mapped FV
> +  @param [in] Depth         Nesting depth of encapsulation sections. Callers
> +                            different from MmCoreFfsFindMmDriver() are
> +                            responsible for passing in a zero Depth.
>  
>    @retval  EFI_SUCCESS            Success.
>    @retval  EFI_INVALID_PARAMETER  Invalid parameter.
> @@ -55,11 +58,15 @@ FvIsBeingProcessed (
>    @retval  EFI_OUT_OF_RESOURCES   Out of resources.
>    @retval  EFI_VOLUME_CORRUPTED   Firmware volume is corrupted.
>    @retval  EFI_UNSUPPORTED        Operation not supported.
> +  @retval  EFI_ABORTED            Recursion aborted because Depth has been
> +                                  greater than or equal to
> +                                  PcdFwVolMmMaxEncapsulationDepth.
>  
>  **/
>  EFI_STATUS
>  MmCoreFfsFindMmDriver (
> -  IN  EFI_FIRMWARE_VOLUME_HEADER  *FwVolHeader
> +  IN  EFI_FIRMWARE_VOLUME_HEADER  *FwVolHeader,
> +  IN  UINT32                      Depth
>    )
>  {
>    EFI_STATUS                  Status;
> @@ -84,6 +91,11 @@ MmCoreFfsFindMmDriver (
>  
>    DEBUG ((DEBUG_INFO, "MmCoreFfsFindMmDriver - 0x%x\n", FwVolHeader));
>  
> +  if (Depth >= PcdGet32 (PcdFwVolMmMaxEncapsulationDepth)) {
> +    DEBUG ((DEBUG_ERROR, "%a: recursion aborted due to nesting depth\n", __func__));
> +    return EFI_ABORTED;
> +  }
> +
>    if (FvHasBeenProcessed (FwVolHeader)) {
>      return EFI_SUCCESS;
>    }
> @@ -172,7 +184,7 @@ MmCoreFfsFindMmDriver (
>      }
>  
>      InnerFvHeader = (VOID *)(Section + 1);
> -    Status        = MmCoreFfsFindMmDriver (InnerFvHeader);
> +    Status        = MmCoreFfsFindMmDriver (InnerFvHeader, Depth + 1);
>      if (EFI_ERROR (Status)) {
>        goto FreeDstBuffer;
>      }
> diff --git a/StandaloneMmPkg/Core/StandaloneMmCore.c b/StandaloneMmPkg/Core/StandaloneMmCore.c
> index d221f1d1115d..523ea0a632a1 100644
> --- a/StandaloneMmPkg/Core/StandaloneMmCore.c
> +++ b/StandaloneMmPkg/Core/StandaloneMmCore.c
> @@ -11,7 +11,8 @@
>  
>  EFI_STATUS
>  MmCoreFfsFindMmDriver (
> -  IN  EFI_FIRMWARE_VOLUME_HEADER  *FwVolHeader
> +  IN  EFI_FIRMWARE_VOLUME_HEADER  *FwVolHeader,
> +  IN  UINT32                      Depth
>    );
>  
>  EFI_STATUS
> @@ -643,7 +644,7 @@ StandaloneMmMain (
>    //
>    DEBUG ((DEBUG_INFO, "Mm Dispatch StandaloneBfvAddress - 0x%08x\n", gMmCorePrivate->StandaloneBfvAddress));
>    if (gMmCorePrivate->StandaloneBfvAddress != 0) {
> -    MmCoreFfsFindMmDriver ((EFI_FIRMWARE_VOLUME_HEADER *)(UINTN)gMmCorePrivate->StandaloneBfvAddress);
> +    MmCoreFfsFindMmDriver ((EFI_FIRMWARE_VOLUME_HEADER *)(UINTN)gMmCorePrivate->StandaloneBfvAddress, 0);
>      MmDispatcher ();
>    }
>  
> diff --git a/StandaloneMmPkg/Core/StandaloneMmCore.inf b/StandaloneMmPkg/Core/StandaloneMmCore.inf
> index c44b9ff33303..02ecd68f37e2 100644
> --- a/StandaloneMmPkg/Core/StandaloneMmCore.inf
> +++ b/StandaloneMmPkg/Core/StandaloneMmCore.inf
> @@ -76,6 +76,9 @@ [Guids]
>    gEfiEventExitBootServicesGuid
>    gEfiEventReadyToBootGuid
>  
> +[Pcd]
> +  gStandaloneMmPkgTokenSpaceGuid.PcdFwVolMmMaxEncapsulationDepth    ##CONSUMES
> +
>  #
>  # This configuration fails for CLANGPDB, which does not support PIE in the GCC
>  # sense. Such however is required for ARM family StandaloneMmCore
> diff --git a/StandaloneMmPkg/StandaloneMmPkg.dec b/StandaloneMmPkg/StandaloneMmPkg.dec
> index 46784d94e421..c43632d6d8ae 100644
> --- a/StandaloneMmPkg/StandaloneMmPkg.dec
> +++ b/StandaloneMmPkg/StandaloneMmPkg.dec
> @@ -48,3 +48,8 @@ [Guids]
>    gEfiStandaloneMmNonSecureBufferGuid      = { 0xf00497e3, 0xbfa2, 0x41a1, { 0x9d, 0x29, 0x54, 0xc2, 0xe9, 0x37, 0x21, 0xc5 }}
>    gEfiArmTfCpuDriverEpDescriptorGuid       = { 0x6ecbd5a1, 0xc0f8, 0x4702, { 0x83, 0x01, 0x4f, 0xc2, 0xc5, 0x47, 0x0a, 0x51 }}
>  
> +[PcdsFixedAtBuild, PcdsPatchableInModule]
> +  ## Maximum permitted encapsulation levels of sections in a firmware volume,
> +  #  in the MM phase. Minimum value is 1. Sections nested more deeply are rejected.
> +  # @Prompt Maximum permitted FwVol section nesting depth (exclusive) in MM.
> +  gStandaloneMmPkgTokenSpaceGuid.PcdFwVolMmMaxEncapsulationDepth|0x10|UINT32|0x00000001

Would it be possible to move the declaration of MmCoreFfsFindMmDriver()
to the header file "StandaloneMmCore.h"?

I find it unfortunate that we currently declare the function in
"StandaloneMmPkg/Core/StandaloneMmCore.c". Should that function
declaration ever diverge from the definition in
"StandaloneMmPkg/Core/FwVol.c", we'd only notice that by a crash
(garbage parameter passing). It's best to have it in the header file, so
that the compiler can check that the call in StandaloneMmMain() and the
actual function definition in "FwVol.c" are in sync.

Apologies for not pointing this out earlier, but I would have not
expected this. After all, we do already have a module-internal header file.

With that update:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thank you!
Laszlo



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