[PATCH] slab: Introduce kmalloc_obj() and family

[Kees Cook <kees@kernel.org>]

Introduce type-aware kmalloc-family helpers to replace the common
idioms for single, array, and flexible object allocations:

	ptr = kmalloc(sizeof(*ptr), gfp);
	ptr = kcalloc(count, sizeof(*ptr), gfp);
	ptr = kmalloc_array(count, sizeof(*ptr), gfp);
	ptr = kcalloc(count, sizeof(*ptr), gfp);
	ptr = kmalloc(struct_size(ptr, flex_member, count), gfp);

These become, respectively:

	kmalloc_obj(p, gfp);
	kzalloc_obj(p, count, gfp);
	kmalloc_obj(p, count, gfp);
	kzalloc_obj(p, count, gfp);
	kmalloc_obj(p, flex_member, count, gfp);

These each return the size of the allocation, so that other common
idioms can be converted easily as well. For example:

	info->size = struct_size(ptr, flex_member, count);
	ptr = kmalloc(info->size, gfp);

becomes:

	info->size = kmalloc_obj(ptr, flex_member, count, gfp);

Internal introspection of allocated type also becomes possible, allowing
for alignment-aware choices and future hardening work. For example,
adding __alignof(*ptr) as an argument to the internal allocators so that
appropriate/efficient alignment choices can be made, or being able to
correctly choose per-allocation offset randomization within a bucket
that does not break alignment requirements.

Additionally, once __builtin_get_counted_by() is added by GCC[1] and
Clang[2], it will be possible to automatically set the counted member of
a struct with a counted_by FAM, further eliminating open-coded redundant
initializations, and can internally check for "too large" allocations
based on the type size of the counter variable:

	if (count > type_max(ptr->flex_count))
		fail...;
	info->size = struct_size(ptr, flex_member, count);
	ptr = kmalloc(info->size, gfp);
	ptr->flex_count = count;

becomes (i.e. unchanged from earlier example):

	info->size = kmalloc_obj(ptr, flex_member, count, gfp);

Replacing all existing simple code patterns found via Coccinelle[3]
shows what could be replaced immediately (saving roughly 1,500 lines):

 7040 files changed, 14128 insertions(+), 15557 deletions(-)

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116016 [1]
Link: https://github.com/llvm/llvm-project/issues/99774 [2]
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/kmalloc_obj-assign-size.cocci [3]
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Cc: Marco Elver <elver@google.com>
Cc: linux-mm@kvack.org
---
 include/linux/slab.h | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index eb2bf4629157..46801c28908e 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -686,6 +686,44 @@ static __always_inline __alloc_size(1) void *kmalloc_noprof(size_t size, gfp_t f
 }
 #define kmalloc(...)				alloc_hooks(kmalloc_noprof(__VA_ARGS__))
 
+#define __alloc_obj3(ALLOC, P, COUNT, FLAGS)			\
+({								\
+	size_t __obj_size = size_mul(sizeof(*P), COUNT);	\
+	void *__obj_ptr;					\
+	(P) = __obj_ptr = ALLOC(__obj_size, FLAGS);		\
+	if (!__obj_ptr)						\
+		__obj_size = 0;					\
+	__obj_size;						\
+})
+
+#define __alloc_obj2(ALLOC, P, FLAGS)	__alloc_obj3(ALLOC, P, 1, FLAGS)
+
+#define __alloc_obj4(ALLOC, P, FAM, COUNT, FLAGS)		\
+({								\
+	size_t __obj_size = struct_size(P, FAM, COUNT);		\
+	void *__obj_ptr;					\
+	(P) = __obj_ptr = ALLOC(__obj_size, FLAGS);		\
+	if (!__obj_ptr)						\
+		__obj_size = 0;					\
+	__obj_size;						\
+})
+
+#define kmalloc_obj(...)					\
+	CONCATENATE(__alloc_obj,				\
+		    COUNT_ARGS(__VA_ARGS__))(kmalloc, __VA_ARGS__)
+
+#define kzalloc_obj(...)					\
+	CONCATENATE(__alloc_obj,				\
+		    COUNT_ARGS(__VA_ARGS__))(kzalloc, __VA_ARGS__)
+
+#define kvmalloc_obj(...)					\
+	CONCATENATE(__alloc_obj,				\
+		    COUNT_ARGS(__VA_ARGS__))(kvmalloc, __VA_ARGS__)
+
+#define kvzalloc_obj(...)					\
+	CONCATENATE(__alloc_obj,				\
+		    COUNT_ARGS(__VA_ARGS__))(kvzalloc, __VA_ARGS__)
+
 #define kmem_buckets_alloc(_b, _size, _flags)	\
 	alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
 
-- 
2.34.1