linux-kernel - Re: [PATCH mm] kasan: reset page tags properly with sampling

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Message-ID: <CA+fCnZeDWxFB0BgUy_tEybtagth=bcGcqqu9LPSOEjKr5j-o8A@mail.gmail.com>
Date:   Tue, 24 Jan 2023 21:46:51 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     andrey.konovalov@...ux.dev, Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH mm] kasan: reset page tags properly with sampling

On Tue, Jan 24, 2023 at 9:45 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 24 Jan 2023 21:35:26 +0100 andrey.konovalov@...ux.dev wrote:
>
> > The implementation of page_alloc poisoning sampling assumed that
> > tag_clear_highpage resets page tags for __GFP_ZEROTAGS allocations.
> > However, this is no longer the case since commit 70c248aca9e7
> > ("mm: kasan: Skip unpoisoning of user pages").
> >
> > This leads to kernel crashes when MTE-enabled userspace mappings are
> > used with Hardware Tag-Based KASAN enabled.
> >
> > Reset page tags for __GFP_ZEROTAGS allocations in post_alloc_hook().
> >
> > Also clarify and fix related comments.
>
> I assume this is a fix against 44383cef54c0 ("kasan: allow sampling
> page_alloc allocations for HW_TAGS") which is presently in mm-stable,
> yes?

Correct. I assumed I shouldn't include a Fixes tag, as the patch is
not in the mainline.