[PATCH v7 22/41] mm/mmap: Add shadow stack pages to memory accounting

[Rick Edgecombe]

From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

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.

Account shadow stack pages to stack memory. Do this by adding a
VM_SHADOW_STACK check in is_stack_mapping().

Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Tested-by: John Allen <john.allen@xxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>

---
v7:
 - Change is_stack_mapping() to know about VM_SHADOW_STACK so the
   additions in vm_stat_account() can be dropped. (David Hildenbrand)

v3:
 - Remove unneeded VM_SHADOW_STACK check in accountable_mapping()
   (Kirill)

v2:
 - Remove is_shadow_stack_mapping() and just change it to directly bitwise
   and VM_SHADOW_STACK.

Yu-cheng v26:
 - Remove redundant #ifdef CONFIG_MMU.

Yu-cheng v25:
 - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for is_shadow_stack_mapping().
---
 mm/internal.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 7920a8b7982e..1d13d5580f64 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -491,14 +491,14 @@ static inline bool is_exec_mapping(vm_flags_t flags)
 }
 
 /*
- * Stack area - automatically grows in one direction
+ * Stack area
  *
- * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous:
- * do_mmap() forbids all other combinations.
+ * 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);
 }
 
 /*
-- 
2.17.1