From 26dc0ef0ff710e89d91089fff79a6fdf5a0ea220 Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Thu, 19 Nov 2020 11:53:39 +0100
Subject: [PATCH 1/2] MdeModulePkg/Core/Dxe: assert SectionInstance invariant
 in FindChildNode()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

FindChildNode() has two callers: GetSection(), and FindChildNode() itself.

- At the GetSection() call site, a positive (i.e., nonzero)
  SectionInstance is passed. This is because GetSection() takes a
  zero-based (UINTN) SectionInstance, and then passes
  Instance=(SectionInstance+1) to FindChildNode().

- For reaching the recursive FindChildNode() call site, a section type
  mismatch, or a section instance mismatch, is necessary. This means,
  respectively, that SectionInstance will either not have been decreased,
  or not to zero anyway, at the recursive FindChildNode() call site.

Add two ASSERT()s to FindChildNode(), for expressing the (SectionSize>0)
invariant.

In turn, the invariant provides the explanation why, after the recursive
call, a zero SectionInstance implies success. Capture it in a comment.

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>
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: <20201119105340.16225-2-lersek@redhat.com>
(cherry picked from commit b9bdfc72853fe97bd24401f8873ca61524dd2dc6)
---
 .../SectionExtraction/CoreSectionExtraction.c | 23 ++++++++++++++-----
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c b/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
index 6622eeeaf161..e9bd70117bef 100644
--- a/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
+++ b/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
@@ -958,8 +958,8 @@ CreateChildNode (
                                  search.
   @param  SearchType             Indicates the type of section to search for.
   @param  SectionInstance        Indicates which instance of section to find.
-                                 This is an in/out parameter to deal with
-                                 recursions.
+                                 This is an in/out parameter and it is 1-based,
+                                 to deal with recursions.
   @param  SectionDefinitionGuid  Guid of section definition
   @param  FoundChild             Output indicating the child node that is found.
   @param  FoundStream            Output indicating which section stream the child
@@ -994,6 +994,8 @@ FindChildNode (
   EFI_STATUS                                    ErrorStatus;
   EFI_STATUS                                    Status;
 
+  ASSERT (*SectionInstance > 0);
+
   CurrentChildNode = NULL;
   ErrorStatus = EFI_NOT_FOUND;
 
@@ -1043,6 +1045,11 @@ FindChildNode (
       }
     }
 
+    //
+    // Type mismatch, or we haven't found the desired instance yet.
+    //
+    ASSERT (*SectionInstance > 0);
+
     if (CurrentChildNode->EncapsulatedStreamHandle != NULL_STREAM_HANDLE) {
       //
       // If the current node is an encapsulating node, recurse into it...
@@ -1056,16 +1063,20 @@ FindChildNode (
                 &RecursedFoundStream,
                 AuthenticationStatus
                 );
-      //
-      // If the status is not EFI_SUCCESS, just save the error code and continue
-      // to find the request child node in the rest stream.
-      //
       if (*SectionInstance == 0) {
+        //
+        // The recursive FindChildNode() call decreased (*SectionInstance) to
+        // zero.
+        //
         ASSERT_EFI_ERROR (Status);
         *FoundChild = RecursedChildNode;
         *FoundStream = RecursedFoundStream;
         return EFI_SUCCESS;
       } else {
+        //
+        // If the status is not EFI_SUCCESS, just save the error code and
+        // continue to find the request child node in the rest stream.
+        //
         ErrorStatus = Status;
       }
     } else if ((CurrentChildNode->Type == EFI_SECTION_GUID_DEFINED) && (SearchType != EFI_SECTION_GUID_DEFINED)) {
-- 
2.29.2


From 57d72547fecf95a7d5f8eb302e9f3bbb2f808182 Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Thu, 19 Nov 2020 11:53:40 +0100
Subject: [PATCH 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>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201119105340.16225-3-lersek@redhat.com>
(cherry picked from commit 47343af30435302c087027177613412a1a83e919)
---
 MdeModulePkg/Core/Dxe/DxeMain.inf             |  1 +
 .../SectionExtraction/CoreSectionExtraction.c | 33 +++++++++++++++++--
 MdeModulePkg/MdeModulePkg.dec                 |  6 ++++
 MdeModulePkg/MdeModulePkg.uni                 |  5 +++
 4 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/DxeMain.inf b/MdeModulePkg/Core/Dxe/DxeMain.inf
index 30d5984f7c1f..c064ad18a81e 100644
--- a/MdeModulePkg/Core/Dxe/DxeMain.inf
+++ b/MdeModulePkg/Core/Dxe/DxeMain.inf
@@ -192,6 +192,7 @@ [Pcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdPropertiesTableEnable                   ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdImageProtectionPolicy                   ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdDxeNxMemoryProtectionPolicy             ## 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 e9bd70117bef..b686f072dbf1 100644
--- a/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
+++ b/MdeModulePkg/Core/Dxe/SectionExtraction/CoreSectionExtraction.c
@@ -961,6 +961,9 @@ 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
@@ -974,6 +977,9 @@ 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
@@ -982,6 +988,7 @@ 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
@@ -996,6 +1003,10 @@ FindChildNode (
 
   ASSERT (*SectionInstance > 0);
 
+  if (Depth >= PcdGet32 (PcdFwVolDxeMaxEncapsulationDepth)) {
+    return EFI_ABORTED;
+  }
+
   CurrentChildNode = NULL;
   ErrorStatus = EFI_NOT_FOUND;
 
@@ -1059,6 +1070,7 @@ FindChildNode (
                 SearchType,
                 SectionInstance,
                 SectionDefinitionGuid,
+                Depth + 1,
                 &RecursedChildNode,
                 &RecursedFoundStream,
                 AuthenticationStatus
@@ -1073,9 +1085,17 @@ 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;
       }
@@ -1278,11 +1298,20 @@ 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;
     }
 
diff --git a/MdeModulePkg/MdeModulePkg.dec b/MdeModulePkg/MdeModulePkg.dec
index ca09cbc10923..6ae004f2bfbb 100644
--- a/MdeModulePkg/MdeModulePkg.dec
+++ b/MdeModulePkg/MdeModulePkg.dec
@@ -1291,6 +1291,12 @@ [PcdsFixedAtBuild, PcdsPatchableInModule]
   # @Prompt CapsuleMax value in capsule report variable.
   gEfiMdeModulePkgTokenSpaceGuid.PcdCapsuleMax|0xFFFF|UINT16|0x00000107
 
+  ## 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 d6015de75fe0..c717aef1eb2a 100644
--- a/MdeModulePkg/MdeModulePkg.uni
+++ b/MdeModulePkg/MdeModulePkg.uni
@@ -1127,3 +1127,8 @@
                                                                                                      "enabled on AMD processors supporting the Secure Encrypted Virtualization (SEV) feature.\n"
                                                                                                      "This mask should be applied when creating 1:1 virtual to physical mapping tables."
 
+#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."
-- 
2.29.2

