linux-kernel - [PATCH 1/2] vmlinux.lds.h: allow arch specific handling of ro_after

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Message-Id: <201606071207.u57C5SHY043074@mx0a-001b2d01.pphosted.com>
Date:	Tue,  7 Jun 2016 14:07:00 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...nel.org>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] vmlinux.lds.h: allow arch specific handling of ro_after_init data section

commit c74ba8b3480d ("arch: Introduce post-init read-only memory")
introduced the __ro_after_init attribute which allows to add variables
to the ro_after_init data section.

This new section was added to rodata, even though it contains writable
data. This in turn causes problems on architectures which mark the
page table entries read-only that point to rodata very early.

This patch allows architectures to implement an own handling of the
.data..ro_after_init section.
Usually that would be:
- mark the rodata section read-only very early
- mark the ro_after_init section read-only within mark_rodata_ro

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 include/asm-generic/vmlinux.lds.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6a67ab94b553..c4436d072d37 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -250,6 +250,14 @@
 	VMLINUX_SYMBOL(__end_init_task) = .;
 
 /*
+ * Allow architectures to handle ro_after_init data on their
+ * own by defining an empty RO_AFTER_INIT_DATA.
+ */
+#ifndef RO_AFTER_INIT_DATA
+#define RO_AFTER_INIT_DATA *(.data..ro_after_init)
+#endif
+
+/*
  * Read only Data
  */
 #define RO_DATA_SECTION(align)						\
@@ -257,7 +265,7 @@
 	.rodata           : AT(ADDR(.rodata) - LOAD_OFFSET) {		\
 		VMLINUX_SYMBOL(__start_rodata) = .;			\
 		*(.rodata) *(.rodata.*)					\
-		*(.data..ro_after_init)	/* Read only after init */	\
+		RO_AFTER_INIT_DATA	/* Read only after init */	\
 		*(__vermagic)		/* Kernel version magic */	\
 		. = ALIGN(8);						\
 		VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .;		\
-- 
2.6.6