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

3 files changed, 45 insertions, 10 deletions

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 445e80517cab..96a4ed11b4be 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -35,7 +35,8 @@
 
 /*
  * Note: do not use this directly. Instead, use __alloc_size() since it is conditionally
- * available and includes other attributes.
+ * available and includes other attributes. For GCC < 9.1, __alloc_size__ gets undefined
+ * in compiler-gcc.h, due to misbehaviors.
  *
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alloc_005fsize-function-attribute
  * clang: https://clang.llvm.org/docs/AttributeReference.html#alloc-size
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 4f2a819fd60a..0717534f8364 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -271,14 +271,16 @@ struct ftrace_likely_data {
 
 /*
  * Any place that could be marked with the "alloc_size" attribute is also
- * a place to be marked with the "malloc" attribute. Do this as part of the
- * __alloc_size macro to avoid redundant attributes and to avoid missing a
- * __malloc marking.
+ * a place to be marked with the "malloc" attribute, except those that may
+ * be performing a _reallocation_, as that may alias the existing pointer.
+ * For these, use __realloc_size().
  */
 #ifdef __alloc_size__
 # define __alloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__) __malloc
+# define __realloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__)
 #else
 # define __alloc_size(x, ...)	__malloc
+# define __realloc_size(x, ...)
 #endif
 
 #ifndef asm_volatile_goto
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 6dc495f76644..6a613e65e78d 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -186,10 +186,25 @@ int kmem_cache_shrink(struct kmem_cache *s);
 /*
  * Common kmalloc functions provided by all allocators
  */
-void * __must_check krealloc(const void *objp, size_t new_size, gfp_t flags) __alloc_size(2);
+void * __must_check krealloc(const void *objp, size_t new_size, gfp_t flags) __realloc_size(2);
 void kfree(const void *objp);
 void kfree_sensitive(const void *objp);
+size_t __ksize(const void *objp);
+
+/**
+ * ksize - Report actual allocation size of associated object
+ *
+ * @objp: Pointer returned from a prior kmalloc()-family allocation.
+ *
+ * This should not be used for writing beyond the originally requested
+ * allocation size. Either use krealloc() or round up the allocation size
+ * with kmalloc_size_roundup() prior to allocation. If this is used to
+ * access beyond the originally requested allocation size, UBSAN_BOUNDS
+ * and/or FORTIFY_SOURCE may trip, since they only know about the
+ * originally allocated size via the __alloc_size attribute.
+ */
 size_t ksize(const void *objp);
+
 #ifdef CONFIG_PRINTK
 bool kmem_valid_obj(void *object);
 void kmem_dump_obj(void *object);
@@ -614,10 +629,10 @@ static inline __alloc_size(1, 2) void *kmalloc_array(size_t n, size_t size, gfp_
  * @new_size: new size of a single member of the array
  * @flags: the type of memory to allocate (see kmalloc)
  */
-static inline __alloc_size(2, 3) void * __must_check krealloc_array(void *p,
-								    size_t new_n,
-								    size_t new_size,
-								    gfp_t flags)
+static inline __realloc_size(2, 3) void * __must_check krealloc_array(void *p,
+								      size_t new_n,
+								      size_t new_size,
+								      gfp_t flags)
 {
 	size_t bytes;
 
@@ -732,11 +747,28 @@ static inline __alloc_size(1, 2) void *kvcalloc(size_t n, size_t size, gfp_t fla
 }
 
 extern void *kvrealloc(const void *p, size_t oldsize, size_t newsize, gfp_t flags)
-		      __alloc_size(3);
+		      __realloc_size(3);
 extern void kvfree(const void *addr);
 extern void kvfree_sensitive(const void *addr, size_t len);
 
 unsigned int kmem_cache_size(struct kmem_cache *s);
+
+/**
+ * kmalloc_size_roundup - Report allocation bucket size for the given size
+ *
+ * @size: Number of bytes to round up from.
+ *
+ * This returns the number of bytes that would be available in a kmalloc()
+ * allocation of @size bytes. For example, a 126 byte request would be
+ * rounded up to the next sized kmalloc bucket, 128 bytes. (This is strictly
+ * for the general-purpose kmalloc()-based allocations, and is not for the
+ * pre-sized kmem_cache_alloc()-based allocations.)
+ *
+ * Use this to kmalloc() the full bucket size ahead of time instead of using
+ * ksize() to query the size after an allocation.
+ */
+size_t kmalloc_size_roundup(size_t size);
+
 void __init kmem_cache_init_late(void);
 
 #if defined(CONFIG_SMP) && defined(CONFIG_SLAB)