[PATCH v2 2/3] kasan: make tag based mode work with CONFIG_HARDENED_USERCOPY

[Andrey Konovalov]

With CONFIG_HARDENED_USERCOPY enabled __check_heap_object() compares and
then subtracts a potentially tagged pointer with a non-tagged address of
the page that this pointer belongs to, which leads to unexpected behavior.

Untag the pointer in __check_heap_object() before doing any of these
operations.

Signed-off-by: Andrey Konovalov <andreyk...@google.com>
---
 mm/slub.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 36c0befeebd8..1e3d0ec4e200 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3846,6 +3846,8 @@ void __check_heap_object(const void *ptr, unsigned long 
n, struct page *page,
        unsigned int offset;
        size_t object_size;
 
+       ptr = kasan_reset_tag(ptr);
+
        /* Find object and usable object size. */
        s = page->slab_cache;
 
-- 
2.20.1.415.g653613c723-goog