slub, kasan: improve interaction of KASAN and slub_debug poisoning

When both KASAN and slub_debug are enabled, when a free object is being
prepared in setup_object, slub_debug poisons the object data before KASAN
initializes its per-object metadata.

Right now, in setup_object, KASAN only initializes the alloc metadata,
which is always stored outside of the object.  slub_debug is aware of this
and it skips poisoning and checking that memory area.

However, with the following patch in this series, KASAN also starts
initializing its free medata in setup_object.  As this metadata might be
stored within the object, this initialization might overwrite the
slub_debug poisoning.  This leads to slub_debug reports.

Thus, skip checking slub_debug poisoning of the object data area that
overlaps with the in-object KASAN free metadata.

Also make slub_debug poisoning of tail kmalloc redzones more precise when
KASAN is enabled: slub_debug can still poison and check the tail kmalloc
allocation area that comes after the KASAN free metadata.

Link: https://lkml.kernel.org/r/20231122231202.121277-1-andrey.konovalov@linux.dev
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Marco Elver <elver@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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