[PATCH] kasan, mm: fix resetting page_alloc tags for HW_TAGS

From: Andrey Konovalov
Date: Tue Jan 19 2021 - 11:45:19 EST

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.

Fixes: aa1ef4d7b3f6 ("kasan, mm: reset tags when accessing metadata")
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
mm/page_alloc.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bdbec4c98173..8ef6fc53962a 100644
--- 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. */
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);