MdeModulePkg/Core/Dxe: limit FwVol encapsulation section recursion

The DXE Core sets up a protocol notify function in its entry point, for
instances of the Firmware Volume Block2 Protocol:

  DxeMain()           [DxeMain/DxeMain.c]
    FwVolDriverInit() [FwVol/FwVol.c]

Assume that a 3rd party UEFI driver or application installs an FVB
instance, with crafted contents. The notification function runs:

  NotifyFwVolBlock() [FwVol/FwVol.c]

installing an instance of the Firmware Volume 2 Protocol on the handle.

(Alternatively, assume that a 3rd party application calls
gDS->ProcessFirmwareVolume(), which may also produce a Firmware Volume 2
Protocol instance.)

The EFI_FIRMWARE_VOLUME2_PROTOCOL.ReadSection() member performs "a
depth-first, left-to-right search algorithm through all sections found in
the specified file" (quoting the PI spec), as follows:

  FvReadFileSection()   [FwVol/FwVolRead.c]
    GetSection()        [SectionExtraction/CoreSectionExtraction.c]
      FindChildNode()   [SectionExtraction/CoreSectionExtraction.c]
        FindChildNode() // recursive call

FindChildNode() 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 FindChildNode() track
the section nesting depth against that PCD.

Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1743
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201119105340.16225-3-lersek@redhat.com>

2 files changed, 32 insertions, 2 deletions

diff --git a/MdeModulePkg/Core/Dxe/DxeMain.inf b/MdeModulePkg/Core/Dxe/DxeMain.inf
index 1d4b11dc73..e4bca89577 100644
--- a/MdeModulePkg/Core/Dxe/DxeMain.inf
+++ b/MdeModulePkg/Core/Dxe/DxeMain.inf
@@ -185,6 +185,7 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPoolType                       ## CONSUMES

   gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPropertyMask                   ## CONSUMES

   gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard                           ## CONSUMES

+  gEfiMdeModulePkgTokenSpaceGuid.PcdFwVolDxeMaxEncapsulationDepth           ## CONSUMES

 

 # [Hob]

 # RESOURCE_DESCRIPTOR   ## CONSUMES

diff --git a/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c b/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
index d7f7ef4274..908617d1ca 100644
--- a/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
+++ b/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
@@ -955,6 +955,9 @@ CreateChildNode (
                                  This is an in/out parameter and it is 1-based,

                                  to deal with recursions.

   @param  SectionDefinitionGuid  Guid of section definition

+  @param  Depth                  Nesting depth of encapsulation sections.

+                                 Callers different from FindChildNode() are

+                                 responsible for passing in a zero Depth.

   @param  FoundChild             Output indicating the child node that is found.

   @param  FoundStream            Output indicating which section stream the child

                                  was found in.  If this stream was generated as a

@@ -968,6 +971,9 @@ CreateChildNode (
   @retval EFI_NOT_FOUND          Requested child node does not exist.

   @retval EFI_PROTOCOL_ERROR     a required GUIDED section extraction protocol

                                  does not exist

+  @retval EFI_ABORTED            Recursion aborted because Depth has been

+                                 greater than or equal to

+                                 PcdFwVolDxeMaxEncapsulationDepth.

 

 **/

 EFI_STATUS

@@ -976,6 +982,7 @@ FindChildNode (
   IN     EFI_SECTION_TYPE                           SearchType,

   IN OUT UINTN                                      *SectionInstance,

   IN     EFI_GUID                                   *SectionDefinitionGuid,

+  IN     UINT32                                     Depth,

   OUT    CORE_SECTION_CHILD_NODE                    **FoundChild,

   OUT    CORE_SECTION_STREAM_NODE                   **FoundStream,

   OUT    UINT32                                     *AuthenticationStatus

@@ -990,6 +997,10 @@ FindChildNode (
 

   ASSERT (*SectionInstance > 0);

 

+  if (Depth >= PcdGet32 (PcdFwVolDxeMaxEncapsulationDepth)) {

+    return EFI_ABORTED;

+  }

+

   CurrentChildNode = NULL;

   ErrorStatus = EFI_NOT_FOUND;

 

@@ -1053,6 +1064,7 @@ FindChildNode (
                 SearchType,

                 SectionInstance,

                 SectionDefinitionGuid,

+                Depth + 1,

                 &RecursedChildNode,

                 &RecursedFoundStream,

                 AuthenticationStatus

@@ -1067,9 +1079,17 @@ FindChildNode (
         *FoundStream = RecursedFoundStream;

         return EFI_SUCCESS;

       } else {

+        if (Status == EFI_ABORTED) {

+          //

+          // If the recursive call was aborted due to nesting depth, stop

+          // looking for the requested child node. The skipped subtree could

+          // throw off the instance counting.

+          //

+          return Status;

+        }

         //

-        // If the status is not EFI_SUCCESS, just save the error code and

-        // continue to find the request child node in the rest stream.

+        // Save the error code and continue to find the requested child node in

+        // the rest of the stream.

         //

         ErrorStatus = Status;

       }

@@ -1272,11 +1292,20 @@ GetSection (
                *SectionType,

                &Instance,

                SectionDefinitionGuid,

+               0,                             // encapsulation depth

                &ChildNode,

                &ChildStreamNode,

                &ExtractedAuthenticationStatus

                );

     if (EFI_ERROR (Status)) {

+      if (Status == EFI_ABORTED) {

+        DEBUG ((DEBUG_ERROR, "%a: recursion aborted due to nesting depth\n",

+          __FUNCTION__));

+        //

+        // Map "aborted" to "not found".

+        //

+        Status = EFI_NOT_FOUND;

+      }

       goto GetSection_Done;

     }