s390/kasan: provide uninstrumented __strlen

s390 kasan code uses sclp_early_printk to report initialization
failures. The code doing that should not be instrumented, because kasan
shadow memory has not been set up yet. Even though sclp_early_core.c is
compiled with instrumentation disabled it uses strlen function, which
is instrumented and would produce shadow memory access if used. To
avoid that, introduce uninstrumented __strlen function to be used
instead.

Before commit 7e0d92f00246 ("s390/kasan: improve string/memory functions
checks") few string functions (including strlen) were escaping kasan
instrumentation due to usage of platform specific versions which are
implemented in inline assembly.

Fixes: 7e0d92f00246 ("s390/kasan: improve string/memory functions checks")
Acked-by: Ilya Leoshkevich <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

arch/s390/include/asm/string.h

···
 #define memcpy(dst, src, len) __memcpy(dst, src, len)
 #define memmove(dst, src, len) __memmove(dst, src, len)
 #define memset(s, c, n) __memset(s, c, n)
+#define strlen(s) __strlen(s)
+
+#define __no_sanitize_prefix_strfunc(x) __##x
 
 #ifndef __NO_FORTIFY
 #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
 #endif
 
+#else
+#define __no_sanitize_prefix_strfunc(x) x
 #endif /* defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__) */
 
 void *__memset16(uint16_t *s, uint16_t v, size_t count);
···
 }
 #endif
 
-#ifdef __HAVE_ARCH_STRLEN
-static inline size_t strlen(const char *s)
+#if defined(__HAVE_ARCH_STRLEN) || (defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__))
+static inline size_t __no_sanitize_prefix_strfunc(strlen)(const char *s)
 {
 	register unsigned long r0 asm("0") = 0;
 	const char *tmp = s;