From ab20b0bdb01fc3e65ff6273893c94013f3e8a0e5 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 30 May 2025 12:06:47 -0700 Subject: [PATCH] overflow: Introduce __DEFINE_FLEX for having no initializer commit 5c78e793f78732b60276401f75cc1a101f9ad121 upstream. While not yet in the tree, there is a proposed patch[1] that was depending on the prior behavior of _DEFINE_FLEX, which did not have an explicit initializer. Provide this via __DEFINE_FLEX now, which can also have attributes applied (e.g. __uninitialized). Examples of the resulting initializer behaviors can be seen here: https://godbolt.org/z/P7Go8Tr33 Link: https://lore.kernel.org/netdev/20250520205920.2134829-9-anthony.l.nguyen@intel.com [1] Fixes: 47e36ed78406 ("overflow: Fix direct struct member initialization in _DEFINE_FLEX()") Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman --- include/linux/overflow.h | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 823a53cd9a19..89e9d6049883 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -388,6 +388,25 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) #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 arbitrary trailing expressions + * + * @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. + * @trailer: Trailing expressions for attributes and/or initializers. + */ +#define __DEFINE_FLEX(type, name, member, count, trailer...) \ + _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 trailer; \ + type *name = (type *)&name##_u + /** * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. * Enables caller macro to pass (different) initializer. @@ -399,13 +418,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * @initializer: Initializer expression (e.g., pass `= { }` at minimum). */ #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 = { .obj initializer }; \ - type *name = (type *)&name##_u + __DEFINE_FLEX(type, name, member, count, = { .obj initializer }) /** * DEFINE_RAW_FLEX() - Define an on-stack instance of structure with a trailing @@ -421,7 +434,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * Use __struct_size(@name) to get compile-time size of it afterwards. */ #define DEFINE_RAW_FLEX(type, name, member, count) \ - _DEFINE_FLEX(type, name, member, count, = {}) + __DEFINE_FLEX(type, name, member, count, = { }) /** * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing