kasan: clean up is_kfence_address checks
1. Do not untag addresses that are passed to is_kfence_address: it
tolerates tagged addresses.
2. Move is_kfence_address checks from internal KASAN functions
(kasan_poison/unpoison, etc.) to external-facing ones.
Note that kasan_poison/unpoison are never called outside of KASAN/slab
code anymore; the comment is wrong, so drop it.
3. Simplify/reorganize the code around the updated checks.
Link: https://lkml.kernel.org/r/1065732315ef4e141b6177d8f612232d4d5bc0ab.1703188911.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>