mm/kasan: introduce __kasan_check_{read,write}

Patch series "mm/kasan: Add object validation in ksize()", v3.

This patch (of 5):

This introduces __kasan_check_{read,write}.  __kasan_check functions may
be used from anywhere, even compilation units that disable instrumentation
selectively.

This change eliminates the need for the __KASAN_INTERNAL definition.

[elver@google.com: v5]
  Link: http://lkml.kernel.org/r/20190708170706.174189-2-elver@google.com
Link: http://lkml.kernel.org/r/20190626142014.141844-2-elver@google.comSigned-off-by: Marco Elver <elver@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kasan-checks.h

@@ -2,9 +2,28 @@
 #ifndef _LINUX_KASAN_CHECKS_H
 #define _LINUX_KASAN_CHECKS_H
 
-#if defined(__SANITIZE_ADDRESS__) || defined(__KASAN_INTERNAL)
-void kasan_check_read(const volatile void *p, unsigned int size);
-void kasan_check_write(const volatile void *p, unsigned int size);
+/*
+ * __kasan_check_*: Always available when KASAN is enabled. This may be used
+ * even in compilation units that selectively disable KASAN, but must use KASAN
+ * to validate access to an address.   Never use these in header files!
+ */
+#ifdef CONFIG_KASAN
+void __kasan_check_read(const volatile void *p, unsigned int size);
+void __kasan_check_write(const volatile void *p, unsigned int size);
+#else
+static inline void __kasan_check_read(const volatile void *p, unsigned int size)
+{ }
+static inline void __kasan_check_write(const volatile void *p, unsigned int size)
+{ }
+#endif
+
+/*
+ * kasan_check_*: Only available when the particular compilation unit has KASAN
+ * instrumentation enabled. May be used in header files.
+ */
+#ifdef __SANITIZE_ADDRESS__
+#define kasan_check_read __kasan_check_read
+#define kasan_check_write __kasan_check_write
 #else
 static inline void kasan_check_read(const volatile void *p, unsigned int size)
 { }

mm/kasan/common.c

@@ -14,8 +14,6 @@
  *
  */
 
-#define __KASAN_INTERNAL
-
 #include <linux/export.h>
 #include <linux/interrupt.h>
 #include <linux/init.h>
@@ -89,17 +87,17 @@ void kasan_disable_current(void)
 	current->kasan_depth--;
 }
 
-void kasan_check_read(const volatile void *p, unsigned int size)
+void __kasan_check_read(const volatile void *p, unsigned int size)
 {
 	check_memory_region((unsigned long)p, size, false, _RET_IP_);
 }
-EXPORT_SYMBOL(kasan_check_read);
+EXPORT_SYMBOL(__kasan_check_read);
 
-void kasan_check_write(const volatile void *p, unsigned int size)
+void __kasan_check_write(const volatile void *p, unsigned int size)
 {
 	check_memory_region((unsigned long)p, size, true, _RET_IP_);
 }
-EXPORT_SYMBOL(kasan_check_write);
+EXPORT_SYMBOL(__kasan_check_write);
 
 #undef memset
 void *memset(void *addr, int c, size_t len)