linux-kernel - Re: [PATCH v2] mm: unexport globally copy_to_kernel

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Message-Id: <8ab6c624-28a1-47b9-93fc-190719c06727@app.fastmail.com>
Date: Sun, 22 Jun 2025 19:44:29 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Sabyrzhan Tasbolatov" <snovitoll@...il.com>,
 "Andrey Konovalov" <andreyknvl@...il.com>
Cc: "Andrew Morton" <akpm@...ux-foundation.org>,
 "David Hildenbrand" <david@...hat.com>, "Dmitry Vyukov" <dvyukov@...gle.com>,
 "Marco Elver" <elver@...gle.com>, "Alexander Potapenko" <glider@...gle.com>,
 "Christoph Hellwig" <hch@...radead.org>, kasan-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 "Andrey Ryabinin" <ryabinin.a.a@...il.com>,
 "Vincenzo Frascino" <vincenzo.frascino@....com>
Subject: Re: [PATCH v2] mm: unexport globally copy_to_kernel_nofault

On Sun, Jun 22, 2025, at 16:11, Sabyrzhan Tasbolatov wrote:
> `copy_to_kernel_nofault()` is an internal helper which should not be
> visible to loadable modules – exporting it would give exploit code a
> cheap oracle to probe kernel addresses.  Instead, keep the helper
> un-exported and compile the kunit case that exercises it only when
> `mm/kasan/kasan_test.o` is linked into vmlinux.
>
> Fixes: ca79a00bb9a8 ("kasan: migrate copy_user_test to kunit")
> Suggested-by: Christoph Hellwig <hch@...radead.org>
> Suggested-by: Marco Elver <elver@...gle.com>
> Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@...il.com>

Acked-by: Arnd Bergmann <arnd@...db.de>