Commit 150a04d8 authored by Bill Wendling's avatar Bill Wendling Committed by Kees Cook
Browse files

compiler_types.h: Attributes: Add __counted_by_ptr macro 

Introduce __counted_by_ptr(), which works like __counted_by(), but for
pointer struct members.

struct foo {
	int a, b, c;
	char *buffer __counted_by_ptr(bytes);
	short nr_bars;
	struct bar *bars __counted_by_ptr(nr_bars);
	size_t bytes;
};

Because "counted_by" can only be applied to pointer members in very
recent compiler versions, its application ends up needing to be distinct
from flexibe array "counted_by" annotations, hence a separate macro.

This is a reworking of Kees' previous patch [1].

Link: https://lore.kernel.org/all/20251020220118.1226740-1-kees@kernel.org/

 [1]
Co-developed-by: default avatarKees Cook <kees@kernel.org>
Signed-off-by: default avatarBill Wendling <morbo@google.com>
Link: https://patch.msgid.link/20260116005838.2419118-1-morbo@google.com


Signed-off-by: default avatarKees Cook <kees@kernel.org>
parent 9f54ab83

Makefile

+6 −0
Original line number Diff line number Diff line
@@ -952,6 +952,12 @@ KBUILD_CFLAGS += $(CC_AUTO_VAR_INIT_ZERO_ENABLER) 
endif

endif



ifdef CONFIG_CC_IS_CLANG

ifdef CONFIG_CC_HAS_COUNTED_BY_PTR

KBUILD_CFLAGS	+= -fexperimental-late-parse-attributes

endif

endif



# Explicitly clear padding bits during variable initialization

KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all)

include/linux/compiler_types.h

+17 −1
Original line number Diff line number Diff line
@@ -369,7 +369,7 @@ struct ftrace_likely_data { 
 * Optional: only supported since clang >= 18

 *

 *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896

 * clang: https://github.com/llvm/llvm-project/pull/76348

 * clang: https://clang.llvm.org/docs/AttributeReference.html#counted-by-counted-by-or-null-sized-by-sized-by-or-null

 *

 * __bdos on clang < 19.1.2 can erroneously return 0:

 * https://github.com/llvm/llvm-project/pull/110497
@@ -383,6 +383,22 @@ struct ftrace_likely_data { 
# define __counted_by(member)

#endif



/*

 * Runtime track number of objects pointed to by a pointer member for use by

 * CONFIG_FORTIFY_SOURCE and CONFIG_UBSAN_BOUNDS.

 *

 * Optional: only supported since gcc >= 16

 * Optional: only supported since clang >= 22

 *

 *   gcc: https://gcc.gnu.org/pipermail/gcc-patches/2025-April/681727.html

 * clang: https://clang.llvm.org/docs/AttributeReference.html#counted-by-counted-by-or-null-sized-by-sized-by-or-null

 */

#ifdef CONFIG_CC_HAS_COUNTED_BY_PTR

#define __counted_by_ptr(member)	__attribute__((__counted_by__(member)))

#else

#define __counted_by_ptr(member)

#endif



/*

 * Optional: only supported since gcc >= 15

 * Optional: not supported by Clang

include/uapi/linux/stddef.h

+4 −0
Original line number Diff line number Diff line
@@ -72,6 +72,10 @@ 
#define __counted_by_be(m)

#endif



#ifndef __counted_by_ptr

#define __counted_by_ptr(m)

#endif



#ifdef __KERNEL__

#define __kernel_nonstring	__nonstring

#else

init/Kconfig

+7 −0
Original line number Diff line number Diff line
@@ -143,6 +143,13 @@ config CC_HAS_COUNTED_BY 
	# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896

	default y if CC_IS_GCC && GCC_VERSION >= 150100



config CC_HAS_COUNTED_BY_PTR

	bool

	# supported since clang 22

	default y if CC_IS_CLANG && CLANG_VERSION >= 220000

	# supported since gcc 16.0.0

	default y if CC_IS_GCC && GCC_VERSION >= 160000



config CC_HAS_MULTIDIMENSIONAL_NONSTRING

	def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)