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>

include/linux/slab.h

@@ -189,14 +189,6 @@ bool kmem_valid_obj(void *object);
 void kmem_dump_obj(void *object);
 #endif
 
-#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
-void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
-			bool to_user);
-#else
-static inline void __check_heap_object(const void *ptr, unsigned long n,
-				       struct page *page, bool to_user) { }
-#endif
-
 /*
  * Some archs want to perform DMA into kmalloc caches and need a guaranteed
  * alignment larger than the alignment of a 64-bit integer.

mm/slab.c

@@ -372,8 +372,8 @@ static void **dbg_userword(struct kmem_cache *cachep, void *objp)
 static int slab_max_order = SLAB_MAX_ORDER_LO;
 static bool slab_max_order_set __initdata;
 
-static inline void *index_to_obj(struct kmem_cache *cache, struct page *page,
-				 unsigned int idx)
+static inline void *index_to_obj(struct kmem_cache *cache,
+				 const struct page *page, unsigned int idx)
 {
 	return page->s_mem + cache->size * idx;
 }
@@ -4166,8 +4166,8 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
  * Returns NULL if check passes, otherwise const char * to name of cache
  * to indicate an error.
  */
-void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
-			 bool to_user)
+void __check_heap_object(const void *ptr, unsigned long n,
+			 const struct slab *slab, bool to_user)
 {
 	struct kmem_cache *cachep;
 	unsigned int objnr;
@@ -4176,15 +4176,15 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 	ptr = kasan_reset_tag(ptr);
 
 	/* Find and validate object. */
-	cachep = page->slab_cache;
-	objnr = obj_to_index(cachep, page, (void *)ptr);
+	cachep = slab->slab_cache;
+	objnr = obj_to_index(cachep, slab_page(slab), (void *)ptr);
 	BUG_ON(objnr >= cachep->num);
 
 	/* Find offset within object. */
 	if (is_kfence_address(ptr))
 		offset = ptr - kfence_object_start(ptr);
 	else
-		offset = ptr - index_to_obj(cachep, page, objnr) - obj_offset(cachep);
+		offset = ptr - index_to_obj(cachep, slab_page(slab), objnr) - obj_offset(cachep);
 
 	/* Allow address range falling entirely within usercopy region. */
 	if (offset >= cachep->useroffset &&

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 */

mm/slub.c

@@ -4485,8 +4485,8 @@ EXPORT_SYMBOL(__kmalloc_node);
  * Returns NULL if check passes, otherwise const char * to name of cache
  * to indicate an error.
  */
-void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
-			 bool to_user)
+void __check_heap_object(const void *ptr, unsigned long n,
+			 const struct slab *slab, bool to_user)
 {
 	struct kmem_cache *s;
 	unsigned int offset;
@@ -4495,18 +4495,18 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 	ptr = kasan_reset_tag(ptr);
 
 	/* Find object and usable object size. */
-	s = page->slab_cache;
+	s = slab->slab_cache;
 
 	/* Reject impossible pointers. */
-	if (ptr < page_address(page))
+	if (ptr < slab_address(slab))
 		usercopy_abort("SLUB object not in SLUB page?!", NULL,
 			       to_user, 0, n);
 
 	/* Find offset within object. */
 	if (is_kfence)
 		offset = ptr - kfence_object_start(ptr);
 	else
-		offset = (ptr - page_address(page)) % s->size;
+		offset = (ptr - slab_address(slab)) % s->size;
 
 	/* Adjust for redzone and reject if within the redzone. */
 	if (!is_kfence && kmem_cache_debug_flags(s, SLAB_RED_ZONE)) {

mm/usercopy.c

@@ -20,6 +20,7 @@
 #include <linux/atomic.h>
 #include <linux/jump_label.h>
 #include <asm/sections.h>
+#include "slab.h"
 
 /*
  * Checks if a given pointer and length is contained by the current
@@ -223,24 +224,24 @@ static inline void check_page_span(const void *ptr, unsigned long n,
 static inline void check_heap_object(const void *ptr, unsigned long n,
 				     bool to_user)
 {
-	struct page *page;
+	struct folio *folio;
 
 	if (!virt_addr_valid(ptr))
 		return;
 
 	/*
 	 * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the
 	 * highmem page or fallback to virt_to_page(). The following
-	 * is effectively a highmem-aware virt_to_head_page().
+	 * is effectively a highmem-aware virt_to_slab().
 	 */
-	page = compound_head(kmap_to_page((void *)ptr));
+	folio = page_folio(kmap_to_page((void *)ptr));
 
-	if (PageSlab(page)) {
+	if (folio_test_slab(folio)) {
 		/* Check slab allocator for flags and size. */
-		__check_heap_object(ptr, n, page, to_user);
+		__check_heap_object(ptr, n, folio_slab(folio), to_user);
 	} else {
 		/* Verify object does not incorrectly span multiple pages. */
-		check_page_span(ptr, n, page, to_user);
+		check_page_span(ptr, n, folio_page(folio, 0), to_user);
 	}
 }