kasan: fix hw tags enablement when KUNIT tests are disabled

Kasan enables hw tags via kasan_enable_tagging() which based on the mode
passed via kernel command line selects the correct hw backend.
kasan_enable_tagging() is meant to be invoked indirectly via the cpu
features framework of the architectures that support these backends.
Currently the invocation of this function is guarded by
CONFIG_KASAN_KUNIT_TEST which allows the enablement of the correct backend
only when KUNIT tests are enabled in the kernel.

This inconsistency was introduced in commit:

  ed6d7444 ("kasan: test: support async (again) and asymm modes for HW_TAGS")

... and prevents to enable MTE on arm64 when KUNIT tests for kasan hw_tags are
disabled.

Fix the issue making sure that the CONFIG_KASAN_KUNIT_TEST guard does not
prevent the correct invocation of kasan_enable_tagging().

Link: https://lkml.kernel.org/r/20220408124323.10028-1-vincenzo.frascino@arm.com
Fixes: ed6d7444 ("kasan: test: support async (again) and asymm modes for HW_TAGS")
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kasan/hw_tags.c

@@ -336,8 +336,6 @@ void __kasan_poison_vmalloc(const void *start, unsigned long size)
 
 #endif
 
-#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
-
 void kasan_enable_tagging(void)
 {
 	if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
@@ -347,6 +345,9 @@ void kasan_enable_tagging(void)
 	else
 		hw_enable_tagging_sync();
 }
+
+#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
+
 EXPORT_SYMBOL_GPL(kasan_enable_tagging);
 
 void kasan_force_async_fault(void)

mm/kasan/kasan.h

@@ -355,25 +355,27 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
 #define hw_set_mem_tag_range(addr, size, tag, init) \
 			arch_set_mem_tag_range((addr), (size), (tag), (init))
 
+void kasan_enable_tagging(void);
+
 #else /* CONFIG_KASAN_HW_TAGS */
 
 #define hw_enable_tagging_sync()
 #define hw_enable_tagging_async()
 #define hw_enable_tagging_asymm()
 
+static inline void kasan_enable_tagging(void) { }
+
 #endif /* CONFIG_KASAN_HW_TAGS */
 
 #if defined(CONFIG_KASAN_HW_TAGS) && IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
 
-void kasan_enable_tagging(void);
 void kasan_force_async_fault(void);
 
-#else /* CONFIG_KASAN_HW_TAGS || CONFIG_KASAN_KUNIT_TEST */
+#else /* CONFIG_KASAN_HW_TAGS && CONFIG_KASAN_KUNIT_TEST */
 
-static inline void kasan_enable_tagging(void) { }
 static inline void kasan_force_async_fault(void) { }
 
-#endif /* CONFIG_KASAN_HW_TAGS || CONFIG_KASAN_KUNIT_TEST */
+#endif /* CONFIG_KASAN_HW_TAGS && CONFIG_KASAN_KUNIT_TEST */
 
 #ifdef CONFIG_KASAN_SW_TAGS
 u8 kasan_random_tag(void);