mm/slab: refactor common ksize KASAN logic into slab_common.c

This refactors common code of ksize() between the various allocators into
slab_common.c: __ksize() is the allocator-specific implementation without
instrumentation, whereas ksize() includes the required KASAN logic.

Link: http://lkml.kernel.org/r/20190626142014.141844-5-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Christoph Lameter <cl@linux.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/slab.h

@@ -184,6 +184,7 @@ void * __must_check __krealloc(const void *, size_t, gfp_t);
 void * __must_check krealloc(const void *, size_t, gfp_t);
 void kfree(const void *);
 void kzfree(const void *);
+size_t __ksize(const void *);
 size_t ksize(const void *);
 
 #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR

mm/slab.c

@@ -4204,20 +4204,12 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 #endif /* CONFIG_HARDENED_USERCOPY */
 
 /**
- * ksize - get the actual amount of memory allocated for a given object
- * @objp: Pointer to the object
+ * __ksize -- Uninstrumented ksize.
  *
- * kmalloc may internally round up allocations and return more memory
- * than requested. ksize() can be used to determine the actual amount of
- * memory allocated. The caller may use this additional memory, even though
- * a smaller amount of memory was initially specified with the kmalloc call.
- * The caller must guarantee that objp points to a valid object previously
- * allocated with either kmalloc() or kmem_cache_alloc(). The object
- * must not be freed during the duration of the call.
- *
- * Return: size of the actual memory used by @objp in bytes
+ * Unlike ksize(), __ksize() is uninstrumented, and does not provide the same
+ * safety checks as ksize() with KASAN instrumentation enabled.
  */
-size_t ksize(const void *objp)
+size_t __ksize(const void *objp)
 {
 	struct kmem_cache *c;
 	size_t size;
@@ -4228,11 +4220,7 @@ size_t ksize(const void *objp)
 
 	c = virt_to_cache(objp);
 	size = c ? c->object_size : 0;
-	/* We assume that ksize callers could use the whole allocated area,
-	 * so we need to unpoison this area.
-	 */
-	kasan_unpoison_shadow(objp, size);
 
 	return size;
 }
-EXPORT_SYMBOL(ksize);
+EXPORT_SYMBOL(__ksize);

mm/slab_common.c

@@ -1597,6 +1597,32 @@ void kzfree(const void *p)
 }
 EXPORT_SYMBOL(kzfree);
 
+/**
+ * ksize - get the actual amount of memory allocated for a given object
+ * @objp: Pointer to the object
+ *
+ * kmalloc may internally round up allocations and return more memory
+ * than requested. ksize() can be used to determine the actual amount of
+ * memory allocated. The caller may use this additional memory, even though
+ * a smaller amount of memory was initially specified with the kmalloc call.
+ * The caller must guarantee that objp points to a valid object previously
+ * allocated with either kmalloc() or kmem_cache_alloc(). The object
+ * must not be freed during the duration of the call.
+ *
+ * Return: size of the actual memory used by @objp in bytes
+ */
+size_t ksize(const void *objp)
+{
+	size_t size = __ksize(objp);
+	/*
+	 * We assume that ksize callers could use whole allocated area,
+	 * so we need to unpoison this area.
+	 */
+	kasan_unpoison_shadow(objp, size);
+	return size;
+}
+EXPORT_SYMBOL(ksize);
+
 /* Tracepoints definitions. */
 EXPORT_TRACEPOINT_SYMBOL(kmalloc);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);

mm/slob.c

@@ -527,7 +527,7 @@ void kfree(const void *block)
 EXPORT_SYMBOL(kfree);
 
 /* can't use ksize for kmem_cache_alloc memory, only kmalloc */
-size_t ksize(const void *block)
+size_t __ksize(const void *block)
 {
 	struct page *sp;
 	int align;
@@ -545,7 +545,7 @@ size_t ksize(const void *block)
 	m = (unsigned int *)(block - align);
 	return SLOB_UNITS(*m) * SLOB_UNIT;
 }
-EXPORT_SYMBOL(ksize);
+EXPORT_SYMBOL(__ksize);
 
 int __kmem_cache_create(struct kmem_cache *c, slab_flags_t flags)
 {

mm/slub.c

@@ -3895,7 +3895,7 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 }
 #endif /* CONFIG_HARDENED_USERCOPY */
 
-static size_t __ksize(const void *object)
+size_t __ksize(const void *object)
 {
 	struct page *page;
 
@@ -3911,17 +3911,7 @@ static size_t __ksize(const void *object)
 
 	return slab_ksize(page->slab_cache);
 }
-
-size_t ksize(const void *object)
-{
-	size_t size = __ksize(object);
-	/* We assume that ksize callers could use whole allocated area,
-	 * so we need to unpoison this area.
-	 */
-	kasan_unpoison_shadow(object, size);
-	return size;
-}
-EXPORT_SYMBOL(ksize);
+EXPORT_SYMBOL(__ksize);
 
 void kfree(const void *x)
 {