linux-kernel - [PATCH v2 01/10] arm64: Move the zero page to rodata

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Message-ID: <20260126092630.1800589-13-ardb+git@google.com>
Date: Mon, 26 Jan 2026 10:26:32 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, will@...nel.org, 
	catalin.marinas@....com, mark.rutland@....com, 
	Ard Biesheuvel <ardb@...nel.org>, Ryan Roberts <ryan.roberts@....com>, 
	Anshuman Khandual <anshuman.khandual@....com>, Liz Prucka <lizprucka@...gle.com>, 
	Seth Jenkins <sethjenkins@...gle.com>, Kees Cook <kees@...nel.org>, 
	linux-hardening@...r.kernel.org
Subject: [PATCH v2 01/10] arm64: Move the zero page to rodata

From: Ard Biesheuvel <ardb@...nel.org>

The zero page should contain only zero bytes, and so mapping it
read-write is unnecessary. Combine it with reserved_pg_dir, which lives
in the read-only region of the kernel, and already serves a similar
purpose.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/kernel/vmlinux.lds.S | 1 +
 arch/arm64/mm/mmu.c             | 3 +--
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index ad6133b89e7a..b2a093f5b3fc 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -229,6 +229,7 @@ SECTIONS
 #endif
 
 	reserved_pg_dir = .;
+	empty_zero_page = .;
 	. += PAGE_SIZE;
 
 	swapper_pg_dir = .;
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9ae7ce00a7ef..c36422a3fae2 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -66,9 +66,8 @@ long __section(".mmuoff.data.write") __early_cpu_boot_status;
 
 /*
  * Empty_zero_page is a special page that is used for zero-initialized data
- * and COW.
+ * and COW. Defined in the linker script.
  */
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
 EXPORT_SYMBOL(empty_zero_page);
 
 static DEFINE_SPINLOCK(swapper_pgdir_lock);
-- 
2.52.0.457.g6b5491de43-goog