jump_table: Move entries into ro_after_init region

The __jump_table sections emitted into the core kernel and into
each module consist of statically initialized references into
other parts of the code, and with the exception of entries that
point into init code, which are defused at post-init time, these
data structures are never modified.

So let's move them into the ro_after_init section, to prevent them
from being corrupted inadvertently by buggy code, or deliberately
by an attacker.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Jessica Yu <jeyu@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-s390@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: https://lkml.kernel.org/r/20180919065144.25010-9-ard.biesheuvel@linaro.org

include/asm-generic/vmlinux.lds.h

@@ -253,10 +253,6 @@
 	STRUCT_ALIGN();							\
 	*(__tracepoints)						\
 	/* implement dynamic printk debug */				\
-	. = ALIGN(8);                                                   \
-	__start___jump_table = .;					\
-	KEEP(*(__jump_table))                                           \
-	__stop___jump_table = .;					\
 	. = ALIGN(8);							\
 	__start___verbose = .;						\
 	KEEP(*(__verbose))                                              \
@@ -300,6 +296,12 @@
 	. = __start_init_task + THREAD_SIZE;				\
 	__end_init_task = .;
 
+#define JUMP_TABLE_DATA							\
+	. = ALIGN(8);							\
+	__start___jump_table = .;					\
+	KEEP(*(__jump_table))						\
+	__stop___jump_table = .;
+
 /*
  * Allow architectures to handle ro_after_init data on their
  * own by defining an empty RO_AFTER_INIT_DATA.
@@ -308,6 +310,7 @@
 #define RO_AFTER_INIT_DATA						\
 	__start_ro_after_init = .;					\
 	*(.data..ro_after_init)						\
+	JUMP_TABLE_DATA							\
 	__end_ro_after_init = .;
 #endif