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Message-Id: <20230811120814.169952-2-przemyslaw.kitszel@intel.com> Date: Fri, 11 Aug 2023 08:08:08 -0400 From: Przemek Kitszel <przemyslaw.kitszel@...el.com> To: Kees Cook <keescook@...omium.org>, netdev@...r.kernel.org Cc: Jacob Keller <jacob.e.keller@...el.com>, intel-wired-lan@...ts.osuosl.org, Alexander Lobakin <aleksander.lobakin@...el.com>, linux-hardening@...r.kernel.org, Steven Zou <steven.zou@...el.com>, Przemek Kitszel <przemyslaw.kitszel@...el.com> Subject: [PATCH net-next v2 1/7] overflow: add DEFINE_FLEX() for on-stack allocs 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. Co-developed-by: Kees Cook <keescook@...omium.org> Signed-off-by: Kees Cook <keescook@...omium.org> Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@...el.com> --- v2: Kees: reuse __struct_size() instead of adding new macro (adding Kees as Co-dev here) v1: change macro name; add macro for size read; accept struct type instead of ptr to it; change alignment; --- include/linux/compiler_types.h | 12 ++++++++++++ include/linux/fortify-string.h | 4 ---- include/linux/overflow.h | 27 +++++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 4 deletions(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 547ea1ff806e..d880c1180de2 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -324,6 +324,18 @@ 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 diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index da51a83b2829..1e7711185ec6 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -93,13 +93,9 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) #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) ( \ diff --git a/include/linux/overflow.h b/include/linux/overflow.h index f9b60313eaea..21a4410799eb 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -309,4 +309,31 @@ 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() - Define a zeroed, on-stack, instance of @type 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 DEFINE_FLEX(type, name, member, count) \ + union { \ + u8 bytes[struct_size_t(type, member, count)]; \ + type obj; \ + } name##_u __aligned(_Alignof(type)) = {}; \ + type *name = (type *)&name##_u + +/** + * const_flex_size() - Get size of on-stack instance of structure with + * a trailing flexible array member. + * + * @name: Name of the variable, the one defined by DEFINE_FLEX() macro above. + * + * Get size of @name, which is equivalent to struct_size(name, array, count), + * but does not require (repeating) last two arguments. + */ +#define const_flex_size(name) __builtin_object_size(name, 1) + #endif /* __LINUX_OVERFLOW_H */ -- 2.40.1
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