linux-hardening - Re: [RFC net-next v4 1/7] overflow: add DEFINE

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Message-ID: <7AB970A3-883F-49A4-BBCD-23E2CD1E869C@kernel.org>
Date:   Mon, 04 Sep 2023 20:55:29 -0700
From:   Kees Cook <kees@...nel.org>
To:     Przemek Kitszel <przemyslaw.kitszel@...el.com>,
        netdev@...r.kernel.org
CC:     Kees Cook <keescook@...omium.org>,
        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>,
        Jakub Kicinski <kuba@...nel.org>,
        Anthony Nguyen <anthony.l.nguyen@...el.com>,
        David Laight <David.Laight@...LAB.COM>
Subject: Re: [RFC net-next v4 1/7] overflow: add DEFINE_FLEX() for on-stack allocs

On September 4, 2023 5:31:01 AM PDT, Przemek Kitszel <przemyslaw.kitszel@...el.com> wrote:
> [...]
>+/**
>+ * _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

Yeah, I like this! This will make it easy to add __counted_by initializers when we have the need in the future.



-- 
Kees Cook