Report on failing tests with thread stack protection and their resolution.

[Sebastian Huber]

On 23/01/2021 07:27, Utkarsh Rai wrote:

> The issue that remains is of User extension iterators, in particular 
> of nested iterators. My idea is to disable memory protection in places 
> during iteration where inter-stack access takes place.  The problem is 
> determining the region for which memory protection needs to be 
> disabled. One way to get around this would be by disabling memory 
> protection for all the stacks, in a blanket-based manner. 

I used this approach for a Nios II system with a thread stack 
protection. We trust the operating system, so this approach should be fine.

diff --git a/cpukit/score/src/userextiterate.c 
b/cpukit/score/src/userextiterate.c
index a25a4ad768..3e56c3a39d 100644
--- a/cpukit/score/src/userextiterate.c
+++ b/cpukit/score/src/userextiterate.c
@@ -34,6 +34,10 @@

  #include <rtems/score/userextimpl.h>

+#ifdef BSP_NIOS2_USE_MPU
+#include <rtems/score/nios2-utility.h>
+#endif
+
  #include <pthread.h>

  User_extensions_List _User_extensions_List = {
@@ -188,6 +192,9 @@ void _User_extensions_Iterate(
    }

    _User_extensions_Acquire( &lock_context );
+#ifdef BSP_NIOS2_USE_MPU
+  uint32_t config = _Nios2_MPU_Disable();
+#endif

    _Chain_Iterator_initialize(
      &_User_extensions_List.Active,
@@ -206,12 +213,18 @@ void _User_extensions_Iterate(

      _Chain_Iterator_set_position( &iter.Iterator, node );

+#ifdef BSP_NIOS2_USE_MPU
+    _Nios2_MPU_Restore( config );
+#endif
      _User_extensions_Release( &lock_context );

      extension = (const User_extensions_Control *) node;
      ( *visitor )( executing, arg, &extension->Callouts );

      _User_extensions_Acquire( &lock_context );
+#ifdef BSP_NIOS2_USE_MPU
+    config = _Nios2_MPU_Disable();
+#endif
    }

    if ( executing != NULL ) {
@@ -220,6 +233,9 @@ void _User_extensions_Iterate(

    _Chain_Iterator_destroy( &iter.Iterator );

+#ifdef BSP_NIOS2_USE_MPU
+  _Nios2_MPU_Restore( config );
+#endif
    _User_extensions_Release( &lock_context );

    if ( direction == CHAIN_ITERATOR_BACKWARD ) {

> The other possibility is to access the last blocked thread and disable 
> memory protection just for the stack of this thread (as inter-stack 
> access of the previously blocked thread takes place during iteration). 
> How to get access to the queue of blocked threads? And is this method 
> feasible?
The system doesn't know the last blocked thread currently. I am not sure 
if knowing the last blocked thread helps you here.

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