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;
};
Since "counted_by" can only be applied to pointer members in very recent
compiler versions, its application ends up needing to be distinct from
flexible array "counted_by" annotations, hence a separate macro.
Unfortunately, this annotation cannot be used for "void *" members
(since such a member is considered a pointer to an incomplete type,
and neither Clang nor GCC developers could be convinced otherwise[1],
even in the face of the GNU extension that "void *" has size "1 byte"
for pointer arithmetic). For "void *" members, we must use the coming
"sized_by" attribute.
Link: https://gcc.gnu.org/pipermail/gcc-patches/2025-May/683136.html [1]
Signed-off-by: Kees Cook <[email protected]>
---
Cc: Miguel Ojeda <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Bill Wendling <[email protected]>
Cc: Justin Stitt <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Przemek Kitszel <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: <[email protected]>
---
init/Kconfig | 11 +++++++++++
Makefile | 4 ++++
include/linux/compiler_types.h | 21 ++++++++++++++++++++-
include/uapi/linux/stddef.h | 4 ++++
4 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index cab3ad28ca49..54691b086bc6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -139,6 +139,17 @@ 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_BARE
+ def_bool $(success,echo 'struct foo { int *ptr
__attribute__((__counted_by__(count))); int count; };' | $(CC) $(CLANG_FLAGS)
-x c - -c -o /dev/null -Werror)
+
+config CC_HAS_COUNTED_BY_PTR_EXP
+ def_bool $(success,echo 'struct foo { int *ptr
__attribute__((__counted_by__(count))); int count; };' | $(CC) $(CLANG_FLAGS)
-fexperimental-late-parse-attributes -x c - -c -o /dev/null -Werror)
+ depends on !CC_HAS_COUNTED_BY_PTR_BARE
+
+config CC_HAS_COUNTED_BY_PTR
+ def_bool y
+ depends on CC_HAS_COUNTED_BY_PTR_BARE || CC_HAS_COUNTED_BY_PTR_EXP
+
config CC_HAS_MULTIDIMENSIONAL_NONSTRING
def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) =
{ };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
diff --git a/Makefile b/Makefile
index d14824792227..1b297dcbb0df 100644
--- a/Makefile
+++ b/Makefile
@@ -933,6 +933,10 @@ KBUILD_CFLAGS += $(CC_AUTO_VAR_INIT_ZERO_ENABLER)
endif
endif
+ifdef CONFIG_CC_HAS_COUNTED_BY_PTR_EXP
+KBUILD_CFLAGS += -fexperimental-late-parse-attributes
+endif
+
# Explicitly clear padding bits during variable initialization
KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all)
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 59288a2c1ad2..f197ea03b593 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -353,11 +353,14 @@ struct ftrace_likely_data {
#endif
/*
+ * Runtime track number of flexible array member elements for use by
+ * CONFIG_FORTIFY_SOURCE and CONFIG_UBSAN_BOUNDS.
+ *
* Optional: only supported since gcc >= 15
* 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
@@ -371,6 +374,22 @@ 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 >= 20
+ *
+ * gcc: https://gcc.gnu.org/pipermail/gcc-patches/2025-April/681727.html
+ * clang: ...
+ */
+#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
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index 9a28f7d9a334..111b097ec00b 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -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
--
2.34.1
