Merge branch 'slab/for-6.1/kmalloc_size_roundup' into slab/for-next

The first two patches from a series by Kees Cook [1] that introduce
kmalloc_size_roundup(). This will allow merging of per-subsystem patches using
the new function and ultimately stop (ab)using ksize() in a way that causes
ongoing trouble for debugging functionality and static checkers.

[1] https://lore.kernel.org/all/20220923202822.2667581-1-keescook@chromium.org/

--
Resolved a conflict of modifying mm/slab.c __ksize() comment with a commit that
unifies __ksize() implementation into mm/slab_common.c

1 files changed, 34 insertions, 3 deletions

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 82c10b4d1203..9ad97ae73a0a 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -734,6 +734,26 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
 	return kmalloc_caches[kmalloc_type(flags)][index];
 }
 
+size_t kmalloc_size_roundup(size_t size)
+{
+	struct kmem_cache *c;
+
+	/* Short-circuit the 0 size case. */
+	if (unlikely(size == 0))
+		return 0;
+	/* Short-circuit saturated "too-large" case. */
+	if (unlikely(size == SIZE_MAX))
+		return SIZE_MAX;
+	/* Above the smaller buckets, size is a multiple of page size. */
+	if (size > KMALLOC_MAX_CACHE_SIZE)
+		return PAGE_SIZE << get_order(size);
+
+	/* The flags don't matter since size_index is common to all. */
+	c = kmalloc_slab(size, GFP_KERNEL);
+	return c ? c->object_size : 0;
+}
+EXPORT_SYMBOL(kmalloc_size_roundup);
+
 #ifdef CONFIG_ZONE_DMA
 #define KMALLOC_DMA_NAME(sz)	.name[KMALLOC_DMA] = "dma-kmalloc-" #sz,
 #else
@@ -987,7 +1007,18 @@ void kfree(const void *object)
 }
 EXPORT_SYMBOL(kfree);
 
-/* Uninstrumented ksize. Only called by KASAN. */
+/**
+ * __ksize -- Report full size of underlying allocation
+ * @objp: pointer to the object
+ *
+ * This should only be used internally to query the true size of allocations.
+ * It is not meant to be a way to discover the usable size of an allocation
+ * after the fact. Instead, use kmalloc_size_roundup(). Using memory beyond
+ * the originally requested allocation size may trigger KASAN, UBSAN_BOUNDS,
+ * and/or FORTIFY_SOURCE.
+ *
+ * Return: size of the actual memory used by @objp in bytes
+ */
 size_t __ksize(const void *object)
 {
 	struct folio *folio;
@@ -1294,8 +1325,8 @@ module_init(slab_proc_init);
 
 #endif /* CONFIG_SLAB || CONFIG_SLUB_DEBUG */
 
-static __always_inline void *__do_krealloc(const void *p, size_t new_size,
-					   gfp_t flags)
+static __always_inline __realloc_size(2) void *
+__do_krealloc(const void *p, size_t new_size, gfp_t flags)
 {
 	void *ret;
 	size_t ks;