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

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Message-Id: <20230124124504.2b21f0fde58af208a4f4e290@linux-foundation.org>
Date:   Tue, 24 Jan 2023 12:45:04 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     andrey.konovalov@...ux.dev
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        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, 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?