On Fri, Dec 10, 2021 at 6:48 PM Catalin Marinas [off-list ref] wrote:

On Mon, Dec 06, 2021 at 10:43:45PM +0100, andrey.konovalov@linux.dev wrote:

quoted

From: Andrey Konovalov <redacted>

__GFP_ZEROTAGS should only be effective if memory is being zeroed.
Currently, hardware tag-based KASAN violates this requirement.

Fix by including an initialization check along with checking for
__GFP_ZEROTAGS.

Signed-off-by: Andrey Konovalov <redacted>
Reviewed-by: Alexander Potapenko <glider@google.com>
---
 mm/kasan/hw_tags.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 0b8225add2e4..c643740b8599 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c

@@ -199,11 +199,12 @@ void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
       * page_alloc.c.
       */
      bool init = !want_init_on_free() && want_init_on_alloc(flags);
+     bool init_tags = init && (flags & __GFP_ZEROTAGS);

      if (flags & __GFP_SKIP_KASAN_POISON)
              SetPageSkipKASanPoison(page);

-     if (flags & __GFP_ZEROTAGS) {
+     if (init_tags) {

You can probably leave this unchanged but add a WARN_ON_ONCE() if !init.
AFAICT there's only a single place where __GFP_ZEROTAGS is passed.

Yes, there's only one such place.

In a later patch, I implement handling __GFP_ZEROTAGS in regardless of
having __GFP_ZERO present or not, so adding WARN_ON() here and then
removing it probably doesn't make much sense.

As per what you said in the other message, I've left this unchanged.

Thanks!