mm: Convert check_heap_object() to use struct slab

Ensure that we're not seeing a tail page inside __check_heap_object() by
converting to a slab instead of a page.  Take the opportunity to mark
the slab as const since we're not modifying it.  Also move the
declaration of __check_heap_object() to mm/slab.h so it's not available
to the wider kernel.

[ vbabka@suse.cz: in check_heap_object() only convert to struct slab for
  actual PageSlab pages; use folio as intermediate step instead of page ]

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Roman Gushchin <guro@fb.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/mm/slab.h b/mm/slab.h
index 9ae9f6c3d1cb..039babfde2fe 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -812,4 +812,15 @@ struct kmem_obj_info {
 void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab);
 #endif
 
+#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
+void __check_heap_object(const void *ptr, unsigned long n,
+			 const struct slab *slab, bool to_user);
+#else
+static inline
+void __check_heap_object(const void *ptr, unsigned long n,
+			 const struct slab *slab, bool to_user)
+{
+}
+#endif
+
 #endif /* MM_SLAB_H */