fortify: Move remaining fortify helpers into fortify-string.h

When commit a28a6e8 ("string.h: move fortified functions definitions
in a dedicated header.") moved the fortify-specific code, some helpers
were left behind. Move the remaining fortify-specific helpers into
fortify-string.h so they're together where they're used. This requires
that any FORTIFY helper function prototypes be conditionally built to
avoid "no prototype" warnings. Additionally removes unused helpers.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Acked-by: Francis Laniel <laniel_francis@privacyrequired.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

include/linux/fortify-string.h

@@ -2,6 +2,13 @@
 #ifndef _LINUX_FORTIFY_STRING_H_
 #define _LINUX_FORTIFY_STRING_H_
 
+#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
+#define __RENAME(x) __asm__(#x)
+
+void fortify_panic(const char *name) __noreturn __cold;
+void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)");
+void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
+void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)");
 
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);

include/linux/string.h

@@ -249,15 +249,6 @@ static inline const char *kbasename(const char *path)
 	return tail ? tail + 1 : path;
 }
 
-#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
-#define __RENAME(x) __asm__(#x)
-
-void fortify_panic(const char *name) __noreturn __cold;
-void __read_overflow(void) __compiletime_error("detected read beyond size of object passed as 1st parameter");
-void __read_overflow2(void) __compiletime_error("detected read beyond size of object passed as 2nd parameter");
-void __read_overflow3(void) __compiletime_error("detected read beyond size of object passed as 3rd parameter");
-void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter");
-
 #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
 #include <linux/fortify-string.h>
 #endif

lib/string_helpers.c

@@ -883,9 +883,11 @@ char *strreplace(char *s, char old, char new)
 }
 EXPORT_SYMBOL(strreplace);
 
+#ifdef CONFIG_FORTIFY_SOURCE
 void fortify_panic(const char *name)
 {
 	pr_emerg("detected buffer overflow in %s\n", name);
 	BUG();
 }
 EXPORT_SYMBOL(fortify_panic);
+#endif /* CONFIG_FORTIFY_SOURCE */