From: Kees Cook <kees@kernel.org>
To: Jann Horn <jannh@google.com>
Cc: Ard Biesheuvel <ardb+git@google.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, will@kernel.org,
catalin.marinas@arm.com, mark.rutland@arm.com,
Ard Biesheuvel <ardb@kernel.org>,
Ryan Roberts <ryan.roberts@arm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Liz Prucka <lizprucka@google.com>,
Seth Jenkins <sethjenkins@google.com>,
Mike Rapoport <rppt@kernel.org>,
David Hildenbrand <david@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init
Date: Mon, 11 May 2026 11:45:39 -0700 [thread overview]
Message-ID: <202605111144.349EF737E@keescook> (raw)
In-Reply-To: <CAG48ez1DJ88a0pBCE-Q0VXyDuJgng8zdunb38g4b4JPU88exww@mail.gmail.com>
On Fri, May 08, 2026 at 07:02:51PM +0200, Jann Horn wrote:
> On Mon, Apr 27, 2026 at 5:44 PM Ard Biesheuvel <ardb+git@google.com> wrote:
> > The empty zero page is used to back any kernel or user space mapping
> > that is supposed to remain cleared, and so the page itself is never
> > supposed to be modified.
> >
> > So make it __ro_after_init rather than __page_aligned_bss: on most
> > architectures, this ensures that both the kernel's mapping of it and any
> > aliases that are accessible via the kernel direct (linear) map are
> > mapped read-only, and cannot be used (inadvertently or maliciously) to
> > corrupt the contents of the zero page.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>
> Reviewed-by: Jann Horn <jannh@google.com>
>
> Sorry, I should have looked at this properly earlier instead of ending
> up duplicating this patch with
> <https://lore.kernel.org/all/20260508-ro-zeropage-v1-1-9808abc20b49@google.com/>.
As you mention in your testing of the patch, could we add an LKDTM test
that does the same to catch any regressions?
--
Kees Cook
next prev parent reply other threads:[~2026-05-11 18:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20260427153416.2103979-17-ardb+git@google.com>
[not found] ` <20260427153416.2103979-19-ardb+git@google.com>
2026-05-08 17:02 ` [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init Jann Horn
2026-05-11 8:59 ` Ard Biesheuvel
2026-05-11 14:40 ` Jann Horn
2026-05-11 18:45 ` Kees Cook [this message]
2026-05-11 19:01 ` Jann Horn
[not found] ` <3d1a6b5c-f3bf-462f-879a-cdb5b60868ac@kernel.org>
2026-05-09 11:04 ` Kiryl Shutsemau
2026-05-11 2:55 ` Feng Tang
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