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b=TtFCNgTA2p/mjwznidoIND1qLBGVv3UQduA0gVwAsewf5q1TlbcO5jwTODxHc5JoN h1RCw0V5QVuBkeotKfTgdSjuW5CO2ySjpRm4tI+y7L7FuAqaa7Dp9QQ69H7u8Ehn7i IC7yJnJQPhLrycdgF17ueA+2wox7S8UIsB00pQqIZomyw2wX/EU2MWDh84xmHzN0sV DJ7XTFv3JBHxH6uuIy352oeNt9n8HWU1MprKg+AIjkg/gVuoVf2oa5dWa2tLl2fAmA c0QmFGBXbzw9Lt5wv4wdPuEWr6Ri4UVEuxyRnGA4fOBleln596cayCqahje7lwUg0V cLm2ZHZXfE+BQ== Date: Tue, 28 Apr 2026 14:27:23 +0200 From: Mike Rapoport To: Ard Biesheuvel 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 , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init Message-ID: References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-19-ardb+git@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260427153416.2103979-19-ardb+git@google.com> X-Rspam-User: X-Rspamd-Queue-Id: E5F2A40004 X-Rspamd-Server: rspam04 X-Stat-Signature: krupbw53ujccbia55mw4gndsd6zjowdq X-HE-Tag: 1777379253-68157 X-HE-Meta: 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 bpLm7Igp 5t+/Piy96Nmf45n+OlvMPj4KFdtO31f9CWdIr1ZOUI9ejPIDSTOBttBXwLr+OP7E6vUkQyGUcbLAu0ObbFso69VGDJ0/aCepxNTDRqOoIu/X53Y243RyVqSdNv0jF467+uAxKzZMuzllDclz/OipOxa9GUya7dBV5TcpF3HK/CYSNBLeJNX0AydF7Wt4IX6y6nKikjEySPGrA54yUOZQW6sbisQpjusaO9HuJNvwdnvZsTMhX0ipVlvfDkSQm3zOk/PVZzwWBhObpMKbgURxrZqu/jYqH8y+6SvylaSCNwDbd+GVU8VGsRbJkvbUS/g8JyQ6G/k3bArp7RQBH7T25wdR8LXQJXzGmmMUND+XfqYpdjVGeeysz/x/YBGZhlrM3xAtngOVyT5F1gktGKp6TZYk5Mw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 27, 2026 at 05:34:19PM +0200, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > 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 Reviewed-by: Mike Rapoport (Microsoft) > --- > 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.