linux-kernel - [PATCH v2 1/3] compiler.h: Move C string helpers into C-only kernel section

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Message-Id: <20250206214014.3567372-1-kees@kernel.org>
Date: Thu,  6 Feb 2025 13:40:06 -0800
From: Kees Cook <kees@...nel.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Kees Cook <kees@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	kernel test robot <lkp@...el.com>,
	Andy Shevchenko <andy@...nel.org>,
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Philipp Reisner <philipp.reisner@...bit.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH v2 1/3] compiler.h: Move C string helpers into C-only kernel section

The C kernel helpers for evaluating C Strings were positioned where they
were visible to assembly inclusion, which was not intended. Move them
into the kernel and C-only area of the header so future changes won't
confuse the assembler.

Fixes: d7a516c6eeae ("compiler.h: Fix undefined BUILD_BUG_ON_ZERO()")
Fixes: 559048d156ff ("string: Check for "nonstring" attribute on strscpy() arguments")
Reviewed-by: Miguel Ojeda <ojeda@...nel.org>
Signed-off-by: Kees Cook <kees@...nel.org>
---
 include/linux/compiler.h | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 240c632c5b95..7af999a131cb 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -214,6 +214,19 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	__v;								\
 })
 
+#ifdef __CHECKER__
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg) (0)
+#else /* __CHECKER__ */
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
+#endif /* __CHECKER__ */
+
+/* &a[0] degrades to a pointer: a different type from an array */
+#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(__same_type((a), &(a)[0]), "must be array")
+
+/* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */
+#define __must_be_cstr(p) \
+	__BUILD_BUG_ON_ZERO_MSG(__annotated(p, nonstring), "must be cstr (NUL-terminated)")
+
 #endif /* __KERNEL__ */
 
 /**
@@ -254,19 +267,6 @@ static inline void *offset_to_ptr(const int *off)
 
 #define __ADDRESSABLE_ASM_STR(sym) __stringify(__ADDRESSABLE_ASM(sym))
 
-#ifdef __CHECKER__
-#define __BUILD_BUG_ON_ZERO_MSG(e, msg) (0)
-#else /* __CHECKER__ */
-#define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
-#endif /* __CHECKER__ */
-
-/* &a[0] degrades to a pointer: a different type from an array */
-#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(__same_type((a), &(a)[0]), "must be array")
-
-/* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */
-#define __must_be_cstr(p) \
-	__BUILD_BUG_ON_ZERO_MSG(__annotated(p, nonstring), "must be cstr (NUL-terminated)")
-
 /*
  * This returns a constant expression while determining if an argument is
  * a constant expression, most importantly without evaluating the argument.
-- 
2.34.1