From: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Date: Tue, 12 Sep 2023 07:59:31 -0400
Subject: overflow: add DEFINE_FLEX() for on-stack allocs
Patch-mainline: v6.7-rc1
Git-commit: 26dd68d293fd1c5ac966fb5dd5f6d89de322a541
References: jsc#PED-4876
Add DEFINE_FLEX() macro for on-stack allocations of structs with
flexible array member.
Expose __struct_size() macro outside of fortify-string.h, as it could be
used to read size of structs allocated by DEFINE_FLEX().
Move __member_size() alongside it.
-Kees
Using underlying array for on-stack storage lets us to declare
known-at-compile-time structures without kzalloc().
Actual usage for ice driver is in following patches of the series.
Missing __has_builtin() workaround is moved up to serve also assembly
compilation with m68k-linux-gcc, see [1].
Error was (note the .S file extension):
In file included from ../include/linux/linkage.h:5,
from ../arch/m68k/fpsp040/skeleton.S:40:
../include/linux/compiler_types.h:331:5: warning: "__has_builtin" is not defined, evaluates to 0 [-Wundef]
331 | #if __has_builtin(__builtin_dynamic_object_size)
| ^~~~~~~~~~~~~
../include/linux/compiler_types.h:331:18: error: missing binary operator before token "("
331 | #if __has_builtin(__builtin_dynamic_object_size)
| ^
[1] https://lore.kernel.org/netdev/202308112122.OuF0YZqL-lkp@intel.com/
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://lore.kernel.org/r/20230912115937.1645707-2-przemyslaw.kitszel@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
include/linux/compiler_types.h | 32 +++++++++++++++++++++-----------
include/linux/fortify-string.h | 4 ----
include/linux/overflow.h | 35 +++++++++++++++++++++++++++++++++++
3 files changed, 56 insertions(+), 15 deletions(-)
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -2,6 +2,15 @@
#ifndef __LINUX_COMPILER_TYPES_H
#define __LINUX_COMPILER_TYPES_H
+/*
+ * __has_builtin is supported on gcc >= 10, clang >= 3 and icc >= 21.
+ * In the meantime, to support gcc < 10, we implement __has_builtin
+ * by hand.
+ */
+#ifndef __has_builtin
+#define __has_builtin(x) (0)
+#endif
+
#ifndef __ASSEMBLY__
/*
@@ -106,17 +115,6 @@ static inline void __chk_io_ptr(const vo
#define __cold
#endif
-/* Builtins */
-
-/*
- * __has_builtin is supported on gcc >= 10, clang >= 3 and icc >= 21.
- * In the meantime, to support gcc < 10, we implement __has_builtin
- * by hand.
- */
-#ifndef __has_builtin
-#define __has_builtin(x) (0)
-#endif
-
/* Compiler specific macros. */
#ifdef __clang__
#include <linux/compiler-clang.h>
@@ -324,6 +322,18 @@ struct ftrace_likely_data {
# define __realloc_size(x, ...)
#endif
+/*
+ * When the size of an allocated object is needed, use the best available
+ * mechanism to find it. (For cases where sizeof() cannot be used.)
+ */
+#if __has_builtin(__builtin_dynamic_object_size)
+#define __struct_size(p) __builtin_dynamic_object_size(p, 0)
+#define __member_size(p) __builtin_dynamic_object_size(p, 1)
+#else
+#define __struct_size(p) __builtin_object_size(p, 0)
+#define __member_size(p) __builtin_object_size(p, 1)
+#endif
+
#ifndef asm_volatile_goto
#define asm_volatile_goto(x...) asm goto(x)
#endif
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -93,13 +93,9 @@ extern char *__underlying_strncpy(char *
#if __has_builtin(__builtin_dynamic_object_size)
#define POS __pass_dynamic_object_size(1)
#define POS0 __pass_dynamic_object_size(0)
-#define __struct_size(p) __builtin_dynamic_object_size(p, 0)
-#define __member_size(p) __builtin_dynamic_object_size(p, 1)
#else
#define POS __pass_object_size(1)
#define POS0 __pass_object_size(0)
-#define __struct_size(p) __builtin_object_size(p, 0)
-#define __member_size(p) __builtin_object_size(p, 1)
#endif
#define __compiletime_lessthan(bounds, length) ( \
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -309,4 +309,39 @@ static inline size_t __must_check size_s
#define struct_size_t(type, member, count) \
struct_size((type *)NULL, member, count)
+/**
+ * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family.
+ * Enables caller macro to pass (different) initializer.
+ *
+ * @type: structure type name, including "struct" keyword.
+ * @name: Name for a variable to define.
+ * @member: Name of the array member.
+ * @count: Number of elements in the array; must be compile-time const.
+ * @initializer: initializer expression (could be empty for no init).
+ */
+#define _DEFINE_FLEX(type, name, member, count, initializer) \
+ _Static_assert(__builtin_constant_p(count), \
+ "onstack flex array members require compile-time const count"); \
+ union { \
+ u8 bytes[struct_size_t(type, member, count)]; \
+ type obj; \
+ } name##_u initializer; \
+ type *name = (type *)&name##_u
+
+/**
+ * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing
+ * flexible array member.
+ *
+ * @type: structure type name, including "struct" keyword.
+ * @name: Name for a variable to define.
+ * @member: Name of the array member.
+ * @count: Number of elements in the array; must be compile-time const.
+ *
+ * Define a zeroed, on-stack, instance of @type structure with a trailing
+ * flexible array member.
+ * Use __struct_size(@name) to get compile-time size of it afterwards.
+ */
+#define DEFINE_FLEX(type, name, member, count) \
+ _DEFINE_FLEX(type, name, member, count, = {})
+
#endif /* __LINUX_OVERFLOW_H */