linux-kernel - Re: [PATCH mm v2 30/33] kasan: implement stack ring for tag-based modes

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Message-ID: <CA+fCnZcT2iXww90CfiByAvr58XHXShiER0x0J2v14hRzNNFe9w@mail.gmail.com>
Date:   Thu, 21 Jul 2022 22:41:36 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     andrey.konovalov@...ux.dev,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Florian Mayer <fmayer@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH mm v2 30/33] kasan: implement stack ring for tag-based modes

On Tue, Jul 19, 2022 at 1:41 PM Marco Elver <elver@...gle.com> wrote:
>
> > +       for (u64 i = pos - 1; i != pos - 1 - KASAN_STACK_RING_SIZE; i--) {
> > +               if (alloc_found && free_found)
> > +                       break;
> > +
> > +               entry = &stack_ring.entries[i % KASAN_STACK_RING_SIZE];
> > +
> > +               /* Paired with smp_store_release() in save_stack_info(). */
> > +               ptr = (void *)smp_load_acquire(&entry->ptr);
> > +
> > +               if (kasan_reset_tag(ptr) != info->object ||
> > +                   get_tag(ptr) != get_tag(info->access_addr))
> > +                       continue;
> > +
> > +               pid = READ_ONCE(entry->pid);
> > +               stack = READ_ONCE(entry->stack);
> > +               is_free = READ_ONCE(entry->is_free);
> > +
> > +               /* Try detecting if the entry was changed while being read. */
> > +               smp_mb();
> > +               if (ptr != (void *)READ_ONCE(entry->ptr))
> > +                       continue;
>
> I thought the re-validation is no longer needed because of the rwlock
> protection?

Oh, yes, forgot to remove this. Will either do in v3 if there are more
things to fix, or will just send a small fix-up patch if the rest of
the series looks good.

> The rest looks fine now.

Thank you, Marco!