[kernel-hardening] [RFC 2/7] init: add set_ro_mostly_after_init_rw/ro function

[Hoeun Ryu <hoeun.ryu@gmail.com>]

 Add set_ro_mostly_after_init_rw/ro pair to modify memory attributes for
memory marked as `ro_mostly_after_init`.

 I am doubtful that this is the right place where these functions reside and
these functions are suitable for all architectures for memory attributes
modification. Please comment.

Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
---
 include/linux/init.h |  6 ++++++
 init/main.c          | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/linux/init.h b/include/linux/init.h
index 79af096..d68e4f7 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -131,6 +131,12 @@ extern bool rodata_enabled;
 #endif
 #ifdef CONFIG_STRICT_KERNEL_RWX
 void mark_rodata_ro(void);
+
+void set_ro_mostly_after_init_rw(void);
+void set_ro_mostly_after_init_ro(void);
+#else
+static inline void set_ro_mostly_after_init_rw(void) { }
+static inline void set_ro_mostly_after_init_ro(void) { }
 #endif
 
 extern void (*late_time_init)(void);
diff --git a/init/main.c b/init/main.c
index 4719abf..a5d4873 100644
--- a/init/main.c
+++ b/init/main.c
@@ -941,6 +941,30 @@ static void mark_readonly(void)
 	} else
 		pr_info("Kernel memory protection disabled.\n");
 }
+
+void set_ro_mostly_after_init_rw(void)
+{
+	unsigned long start = PFN_ALIGN(__start_data_ro_mostly_after_init);
+	unsigned long end = PFN_ALIGN(&__end_data_ro_mostly_after_init);
+	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
+
+	if (!rodata_enabled)
+		return;
+
+	set_memory_rw(start, nr_pages);
+}
+
+void set_ro_mostly_after_init_ro(void)
+{
+	unsigned long start = PFN_ALIGN(__start_data_ro_mostly_after_init);
+	unsigned long end = PFN_ALIGN(&__end_data_ro_mostly_after_init);
+	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
+
+	if (!rodata_enabled)
+		return;
+
+	set_memory_ro(start, nr_pages);
+}
 #else
 static inline void mark_readonly(void)
 {
-- 
2.7.4