kasan, mm: fix resetting page_alloc tags for HW_TAGS

A previous commit added resetting KASAN page tags to
kernel_init_free_pages() to avoid false-positives due to accesses to
metadata with the hardware tag-based mode.

That commit did reset page tags before the metadata access, but didn't
restore them after.  As the result, KASAN fails to detect bad accesses
to page_alloc allocations on some configurations.

Fix this by recovering the tag after the metadata access.

Link: https://lkml.kernel.org/r/02b5bcd692e912c27d484030f666b350ad7e4ae4.1611074450.git.andreyknvl@google.com
Fixes: aa1ef4d7b3f6 ("kasan, mm: reset tags when accessing metadata")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 85ecaa6..783913e 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1207,8 +1207,10 @@ static void kernel_init_free_pages(struct page *page, int numpages)
        /* s390's use of memset() could override KASAN redzones. */
        kasan_disable_current();
        for (i = 0; i < numpages; i++) {
+               u8 tag = page_kasan_tag(page + i);
                page_kasan_tag_reset(page + i);
                clear_highpage(page + i);
+               page_kasan_tag_set(page + i, tag);
        }
        kasan_enable_current();
 }