From 5d02b0176fb8584e44c1b8f2bc1f934e23b017ed Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Mon, 28 Sep 2020 15:02:02 +0200
Subject: [PATCH v2 2/2] MdeModulePkg/Core/Dxe: limit FwVol encapsulation
 section recursion
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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>
---

Notes:
    v2:
    - change the DEC default of the new PCD
      (PcdFwVolDxeMaxEncapsulationDepth) from 8 to 16 (0x10) [Liming]

 MdeModulePkg/MdeModulePkg.dec                                   |  6 ++++
 MdeModulePkg/MdeModulePkg.uni                                   |  6 ++++
 MdeModulePkg/Core/Dxe/DxeMain.inf                               |  1 +
 MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c | 33 ++++++++++++++++++--
 4 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/MdeModulePkg.dec b/MdeModulePkg/MdeModulePkg.dec
index cb30a7975849..eac19a6edcc5 100644
--- a/MdeModulePkg/MdeModulePkg.dec
+++ b/MdeModulePkg/MdeModulePkg.dec
@@ -1505,6 +1505,12 @@ [PcdsFixedAtBuild, PcdsPatchableInModule]
   # @Prompt Enable Capsule On Disk support.
   gEfiMdeModulePkgTokenSpaceGuid.PcdCapsuleOnDiskSupport|FALSE|BOOLEAN|0x0000002d
 
+  ## Maximum permitted encapsulation levels of sections in a firmware volume,
+  #  in the DXE phase. Minimum value is 1. Sections nested more deeply are
+  #  rejected.
+  # @Prompt Maximum permitted FwVol section nesting depth (exclusive).
+  gEfiMdeModulePkgTokenSpaceGuid.PcdFwVolDxeMaxEncapsulationDepth|0x10|UINT32|0x00000030
+
 [PcdsPatchableInModule, PcdsDynamic, PcdsDynamicEx]
   ## This PCD defines the Console output row. The default value is 25 according to UEFI spec.
   #  This PCD could be set to 0 then console output would be at max column and max row.
diff --git a/MdeModulePkg/MdeModulePkg.uni b/MdeModulePkg/MdeModulePkg.uni
index b8c867379a86..9b1be3220fad 100644
--- a/MdeModulePkg/MdeModulePkg.uni
+++ b/MdeModulePkg/MdeModulePkg.uni
@@ -1153,6 +1153,12 @@
                                                                                            "Note:<BR>"
                                                                                            "If Both Capsule In Ram and Capsule On Disk are provisioned at the same time, the Capsule On Disk will be bypassed."
 
+#string STR_gEfiMdeModulePkgTokenSpaceGuid_PcdFwVolDxeMaxEncapsulationDepth_PROMPT #language en-US "Maximum permitted FwVol section nesting depth (exclusive)."
+
+#string STR_gEfiMdeModulePkgTokenSpaceGuid_PcdFwVolDxeMaxEncapsulationDepth_HELP   #language en-US "Maximum permitted encapsulation levels of sections in a firmware volume,<BR>"
+                                                                                                   "in the DXE phase. Minimum value is 1. Sections nested more deeply are<BR>"
+                                                                                                   "rejected."
+
 #string STR_gEfiMdeModulePkgTokenSpaceGuid_PcdCapsuleInRamSupport_PROMPT  #language en-US "Enable Capsule In Ram support"
 
 #string STR_gEfiMdeModulePkgTokenSpaceGuid_PcdCapsuleInRamSupport_HELP  #language en-US   "Capsule In Ram is to use memory to deliver the capsules that will be processed after system reset.<BR><BR>"
diff --git a/MdeModulePkg/Core/Dxe/DxeMain.inf b/MdeModulePkg/Core/Dxe/DxeMain.inf
index 1d4b11dc7318..e4bca895773d 100644
--- a/MdeModulePkg/Core/Dxe/DxeMain.inf
+++ b/MdeModulePkg/Core/Dxe/DxeMain.inf
@@ -185,6 +185,7 @@ [Pcd]
   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 d7f7ef427422..908617d1ca5c 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;
     }
 
-- 
2.19.1.3.g30247aa5d201