mm/mmap: Add shadow stack pages to memory accounting

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual properties, which requires some core mm changes to function
properly.

Co-developed-by: Yu-cheng Yu <[email protected]>
Signed-off-by: Yu-cheng Yu <[email protected]>
Signed-off-by: Rick Edgecombe <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Acked-by: Mike Rapoport (IBM) <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Tested-by: Pengfei Xu <[email protected]>
Tested-by: John Allen <[email protected]>
Tested-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/all/20230613001108.3040476-20-rick.p.edgecombe%40intel.com

Author: rpedgeco

mm/internal.h

@@ -538,14 +538,14 @@ static inline bool is_exec_mapping(vm_flags_t flags)
 }
 
 /*
- * Stack area - automatically grows in one direction
+ * Stack area (including shadow stacks)
  *
  * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous:
  * do_mmap() forbids all other combinations.
  */
 static inline bool is_stack_mapping(vm_flags_t flags)
 {
-	return (flags & VM_STACK) == VM_STACK;
+	return ((flags & VM_STACK) == VM_STACK) || (flags & VM_SHADOW_STACK);
 }
 
 /*