From: Mike Rapoport <rppt@kernel.org>
To: Ard Biesheuvel <ardb+git@google.com>
Cc: 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>,
Kees Cook <kees@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: Tue, 28 Apr 2026 14:27:23 +0200 [thread overview]
Message-ID: <afCnq17NWvM4T4vC@kernel.org> (raw)
In-Reply-To: <20260427153416.2103979-19-ardb+git@google.com>
On Mon, Apr 27, 2026 at 05:34:19PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
>
> 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: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> mm/mm_init.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f9f8e1af921c..6ca01ed2a5a4 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -57,7 +57,7 @@ unsigned long zero_page_pfn __ro_after_init;
> EXPORT_SYMBOL(zero_page_pfn);
>
> #ifndef __HAVE_COLOR_ZERO_PAGE
> -uint8_t empty_zero_page[PAGE_SIZE] __page_aligned_bss;
> +uint8_t empty_zero_page[PAGE_SIZE] __ro_after_init __aligned(PAGE_SIZE);
> EXPORT_SYMBOL(empty_zero_page);
>
> struct page *__zero_page __ro_after_init;
> --
> 2.54.0.rc2.544.gc7ae2d5bb8-goog
>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2026-04-28 12:27 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 15:34 [PATCH v4 00/15] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 01/15] arm64: mm: Map the linear alias of text/rodata as tagged Ard Biesheuvel
2026-04-28 14:16 ` Kevin Brodsky
2026-04-28 16:23 ` Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init Ard Biesheuvel
2026-04-28 12:27 ` Mike Rapoport [this message]
2026-04-28 14:16 ` Kevin Brodsky
2026-04-28 19:51 ` David Hildenbrand (Arm)
2026-04-27 15:34 ` [PATCH v4 03/15] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 04/15] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 05/15] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-04-28 14:33 ` Kevin Brodsky
2026-04-27 15:34 ` [PATCH v4 06/15] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-04-28 14:33 ` Kevin Brodsky
2026-04-27 15:34 ` [PATCH v4 07/15] arm64: mm: Permit contiguous descriptors to be rewritten Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 08/15] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 09/15] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 10/15] arm64: Move fixmap page tables to end of kernel image Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 11/15] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 12/15] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 13/15] arm64: mm: Unmap kernel data/bss entirely from " Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 14/15] arm64: mm: Generalize manipulation code of read-only descriptors Ard Biesheuvel
2026-04-27 15:34 ` [PATCH v4 15/15] arm64: mm: Remap linear aliases of the fixmap page tables read-only Ard Biesheuvel
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