linux-kernel - [PATCH v2 1/2] asm-generic/vmlinux.lds: Move .data.rel.ro input into .rodata segment

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Message-ID: <20250219105542.2418786-5-ardb+git@google.com>
Date: Wed, 19 Feb 2025 11:55:44 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Huacai Chen <chenhuacai@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, 
	stable@...r.kernel.org
Subject: [PATCH v2 1/2] asm-generic/vmlinux.lds: Move .data.rel.ro input into
 .rodata segment

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

When using -fPIE codegen, the compiler will emit const global objects
(which are useless unless statically initialized) into .data.rel.ro
rather than .rodata if the object contains fields that carry absolute
addresses of other code or data objects. This permits the linker to
annotate such regions as requiring read-write access only at load time,
but not at execution time (in user space).

This distinction does not matter for the kernel, but it does imply that
const data will end up in writable memory if the .data.rel.ro sections
are not treated in a special way.

So emit .data.rel.ro into the .rodata segment.

Cc: <stable@...r.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 include/asm-generic/vmlinux.lds.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 02a4adb4a999..0d5b186abee8 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -457,7 +457,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 	. = ALIGN((align));						\
 	.rodata           : AT(ADDR(.rodata) - LOAD_OFFSET) {		\
 		__start_rodata = .;					\
-		*(.rodata) *(.rodata.*)					\
+		*(.rodata) *(.rodata.*) *(.data.rel.ro*)		\
 		SCHED_DATA						\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
 		. = ALIGN(8);						\
-- 
2.48.1.601.g30ceb7b040-goog