[edk2-devel] [PATCH v2 4/4] StandaloneMmPkg: Disallow unregister MMI handler in other MMI handler

["Zhiguang Liu" <zhiguang.liu@intel.com>]

In last patch, we add code support to unregister MMI handler inside
itself. However, the code doesn't support unregister MMI handler
insider other MMI handler. While this is not a must-have usage.
So add check to disallow unregister MMI handler in other MMI handler.

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
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: Zhiguang Liu <zhiguang.liu@intel.com>
---
 StandaloneMmPkg/Core/Mmi.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/StandaloneMmPkg/Core/Mmi.c b/StandaloneMmPkg/Core/Mmi.c
index c1a1d76e85..54794c6b3d 100644
--- a/StandaloneMmPkg/Core/Mmi.c
+++ b/StandaloneMmPkg/Core/Mmi.c
@@ -36,8 +36,9 @@ typedef struct {
   MMI_ENTRY                     *MmiEntry;
 } MMI_HANDLER;
 
-LIST_ENTRY  mRootMmiHandlerList = INITIALIZE_LIST_HEAD_VARIABLE (mRootMmiHandlerList);
-LIST_ENTRY  mMmiEntryList       = INITIALIZE_LIST_HEAD_VARIABLE (mMmiEntryList);
+LIST_ENTRY   mRootMmiHandlerList = INITIALIZE_LIST_HEAD_VARIABLE (mRootMmiHandlerList);
+LIST_ENTRY   mMmiEntryList       = INITIALIZE_LIST_HEAD_VARIABLE (mMmiEntryList);
+MMI_HANDLER  *gCurrentMmiHandler = NULL;
 
 /**
   Finds the MMI entry for the requested handler type.
@@ -161,13 +162,19 @@ MmiManage (
     // get next node before handler is executed, since LIST_ENTRY that
     // Link points to may be freed if unregister MMI handler.
     //
-    Link   = Link->ForwardLink;
-    Status = MmiHandler->Handler (
-                           (EFI_HANDLE)MmiHandler,
-                           Context,
-                           CommBuffer,
-                           CommBufferSize
-                           );
+    Link = Link->ForwardLink;
+    //
+    // Assign gCurrentMmiHandle before calling the MMI handler and
+    // set to NULL when it returns.
+    //
+    gCurrentMmiHandler = MmiHandler;
+    Status             = MmiHandler->Handler (
+                                       (EFI_HANDLE)MmiHandler,
+                                       Context,
+                                       CommBuffer,
+                                       CommBufferSize
+                                       );
+    gCurrentMmiHandler = NULL;
 
     switch (Status) {
       case EFI_INTERRUPT_PENDING:
@@ -314,6 +321,16 @@ MmiHandlerUnRegister (
     return EFI_INVALID_PARAMETER;
   }
 
+  //
+  // Check if unregister MMI handler inside a MMI Handler
+  //
+  if (gCurrentMmiHandler != NULL) {
+    //
+    // Only allow to unregister MMI Handler inside itself.
+    //
+    ASSERT (gCurrentMmiHandler == MmiHandler);
+  }
+
   MmiEntry = MmiHandler->MmiEntry;
 
   RemoveEntryList (&MmiHandler->Link);
-- 
2.31.1.windows.1



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