[Patch 2/2] QuarkSocPkg/QncSmmDispatcher: Fix use after free issue

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

Update Quark North Cluster SMM dispatcher logic to handle
case where an SMI handler unregisters itself.

https://bugzilla.tianocore.org/show_bug.cgi?id=51

This issue was reproduced using the unit test at:

https://github.com/mdkinney/edk2/tree/Bug51/Reproduce

An ASSERT() is generated the 4th time the periodic SMI
handler is triggered when the periodic SMI handler
unregisters itself.  After applying this patch, the
DEBUG() message from the periodic SMI handler in this
unit test is generated 4 times, the periodic SMI handler
is unregistered, and the UEFI Shell works as expected.

Cc: Kelly Steele <kelly.steele@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
---
 .../Smm/DxeSmm/QncSmmDispatcher/QNCSmm.h           |  2 ++
 .../Smm/DxeSmm/QncSmmDispatcher/QNCSmmCore.c       | 41 +++++++++++++++++++---
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmm.h b/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmm.h
index 797be16..ccf9dae 100644
--- a/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmm.h
+++ b/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmm.h
@@ -387,6 +387,8 @@ struct _DATABASE_RECORD {
   UINT32                Signature;
   LIST_ENTRY            Link;
 
+  BOOLEAN               Processed;
+
   //
   // Status and Enable bit description
   //
diff --git a/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmmCore.c b/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmmCore.c
index 4783406..c2f75f8 100644
--- a/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmmCore.c
+++ b/QuarkSocPkg/QuarkNorthCluster/Smm/DxeSmm/QncSmmDispatcher/QNCSmmCore.c
@@ -592,6 +592,7 @@ QNCSmmCoreDispatcher (
   BOOLEAN             ChildWasDispatched;
 
   DATABASE_RECORD     *RecordInDb;
+  DATABASE_RECORD     ActiveRecordInDb;
   LIST_ENTRY          *LinkInDb;
   DATABASE_RECORD     *RecordToExhaust;
   LIST_ENTRY          *LinkToExhaust;
@@ -614,6 +615,16 @@ QNCSmmCoreDispatcher (
   ChildWasDispatched    = FALSE;
 
   //
+  // Mark all child handlers as not processed
+  //
+  LinkInDb = GetFirstNode (&mPrivateData.CallbackDataBase);
+  while (!IsNull (&mPrivateData.CallbackDataBase, LinkInDb)) {
+    RecordInDb = DATABASE_RECORD_FROM_LINK (LinkInDb);
+    RecordInDb->Processed = FALSE;
+    LinkInDb = GetNextNode (&mPrivateData.CallbackDataBase, LinkInDb);
+  }
+
+  //
   // Preserve Index registers
   //
   SaveState ();
@@ -634,6 +645,12 @@ QNCSmmCoreDispatcher (
 
       while ((!IsNull (&mPrivateData.CallbackDataBase, LinkInDb)) && (ResetListSearch == FALSE)) {
         RecordInDb = DATABASE_RECORD_FROM_LINK (LinkInDb);
+        //
+        // Make a copy of the record that contains an active SMI source,
+        // because un-register maybe invoked in callback function and
+        // RecordInDb maybe released
+        //
+        CopyMem (&ActiveRecordInDb, RecordInDb, sizeof (ActiveRecordInDb));
 
         //
         // look for the first active source
@@ -663,6 +680,13 @@ QNCSmmCoreDispatcher (
           //
           while (!IsNull (&mPrivateData.CallbackDataBase, LinkToExhaust)) {
             RecordToExhaust = DATABASE_RECORD_FROM_LINK (LinkToExhaust);
+            LinkToExhaust = GetNextNode (&mPrivateData.CallbackDataBase, LinkToExhaust);
+            if (RecordToExhaust->Processed) {
+              //
+              // Record has already been processed.  Continue with next child handler.
+              //
+              continue;
+            }
 
             if (CompareSources (&RecordToExhaust->SrcDesc, &ActiveSource)) {
               //
@@ -692,6 +716,11 @@ QNCSmmCoreDispatcher (
                 ContextsMatch = TRUE;
               }
 
+              //
+              // Mark this child handler so it will not be processed again
+              //
+              RecordToExhaust->Processed = TRUE;
+
               if (ContextsMatch) {
 
                 if (RecordToExhaust->BufferSize != 0) {
@@ -720,11 +749,13 @@ QNCSmmCoreDispatcher (
                   SxChildWasDispatched = TRUE;
                 }
               }
+              //
+              // Can not use RecordInDb after this point because Callback may have unregistered RecordInDb
+              // Restart processing of SMI handlers from the begining of the linked list because the
+              // state of the linked listed may have been modified due to unregister actions in the Callback.
+              //
+              LinkToExhaust = GetFirstNode (&mPrivateData.CallbackDataBase);
             }
-            //
-            // Get next record in DB
-            //
-            LinkToExhaust = GetNextNode (&mPrivateData.CallbackDataBase, &RecordToExhaust->Link);
           }
 
           if (RecordInDb->ClearSource == NULL) {
@@ -736,7 +767,7 @@ QNCSmmCoreDispatcher (
             //
             // This source requires special handling to clear
             //
-            RecordInDb->ClearSource (&ActiveSource);
+            ActiveRecordInDb.ClearSource (&ActiveSource);
           }
 
           if (ChildWasDispatched) {
-- 
2.6.3.windows.1