Date:   Tue, 24 Jan 2023 12:45:04 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     andrey.konovalov@linux.dev
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>,
        Peter Collingbourne <pcc@google.com>
Subject: Re: [PATCH mm] kasan: reset page tags properly with sampling
Message-Id: <20230124124504.2b21f0fde58af208a4f4e290@linux-foundation.org>
In-Reply-To: <24ea20c1b19c2b4b56cf9f5b354915f8dbccfc77.1674592496.git.andreyknvl@google.com>
References: <24ea20c1b19c2b4b56cf9f5b354915f8dbccfc77.1674592496.git.andreyknvl@google.com>
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On Tue, 24 Jan 2023 21:35:26 +0100 andrey.konovalov@linux.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?