kasan: simplify assign_tag and set_tag calls

set_tag() already ignores the tag for the generic mode, so just call it
as is. Add a check for the generic mode to assign_tag(), and simplify its
call in ____kasan_kmalloc().

Link: https://lkml.kernel.org/r/121eeab245f98555862b289d2ba9269c868fbbcf.1606162397.git.andreyknvl@google.com
Link: https://linux-review.googlesource.com/id/I18905ca78fb4a3d60e1a34a4ca00247272480438Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kasan/common.c

@@ -233,6 +233,9 @@ void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
 static u8 assign_tag(struct kmem_cache *cache, const void *object,
 			bool init, bool keep_tag)
 {
+	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+		return 0xff;
+
 	/*
 	 * 1. When an object is kmalloc()'ed, two hooks are called:
 	 *    kasan_slab_alloc() and kasan_kmalloc(). We assign the
@@ -275,8 +278,8 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
 		__memset(alloc_meta, 0, sizeof(*alloc_meta));
 	}
 
-	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
-		object = set_tag(object, assign_tag(cache, object, true, false));
+	/* Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS */
+	object = set_tag(object, assign_tag(cache, object, true, false));
 
 	return (void *)object;
 }
@@ -360,7 +363,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
 {
 	unsigned long redzone_start;
 	unsigned long redzone_end;
-	u8 tag = 0xff;
+	u8 tag;
 
 	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();
@@ -372,9 +375,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
 				KASAN_GRANULE_SIZE);
 	redzone_end = round_up((unsigned long)object + cache->object_size,
 				KASAN_GRANULE_SIZE);
-
-	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
-		tag = assign_tag(cache, object, false, keep_tag);
+	tag = assign_tag(cache, object, false, keep_tag);
 
 	/* Tag is ignored in set_tag without CONFIG_KASAN_SW/HW_TAGS */
 	unpoison_range(set_tag(object, tag), size);