linux-kernel - [PATCH] arm: ftrace: fix dynamic ftrace with DEBUG_RODATA and !FRAME

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Date:   Wed, 15 Mar 2017 18:07:39 +0000
From:   Abel Vesa <abelvesa@...ux.com>
To:     nicstange@...il.com, rabin@....in, keescook@...omium.org
Cc:     Abel Vesa <abelvesa@...ux.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm: ftrace: fix dynamic ftrace with DEBUG_RODATA and !FRAME_POINTER

The support for dynamic ftrace with CONFIG_DEBUG_RODATA involves
overriding the weak arch_ftrace_update_code() with a variant which makes
the kernel text writable around the patching.

This override was however added under the CONFIG_OLD_MCOUNT ifdef, and
CONFIG_OLD_MCOUNT is only enabled if frame pointers are enabled.

This leads to non-functional dynamic ftrace (ftrace triggers a
WARN_ON()) when CONFIG_DEBUG_RODATA is enabled and CONFIG_FRAME_POINTER
is not.

Move the override out of that ifdef and into the CONFIG_DYNAMIC_FTRACE
ifdef where it belongs.

Fixes: 80d6b0c2eed2a ("ARM: mm: allow text and rodata sections to be read-only")

Suggested-by: Nicolai Stange <nicstange@...il.com>
Suggested-by: Rabin Vincent <rabin@....in>
Signed-off-by: Abel Vesa <abelvesa@...ux.com>
---
 arch/arm/kernel/ftrace.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 3f17594..414e60e 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -29,11 +29,6 @@
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE
-#ifdef CONFIG_OLD_MCOUNT
-#define OLD_MCOUNT_ADDR	((unsigned long) mcount)
-#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
-
-#define	OLD_NOP		0xe1a00000	/* mov r0, r0 */
 
 static int __ftrace_modify_code(void *data)
 {
@@ -51,6 +46,12 @@ void arch_ftrace_update_code(int command)
 	stop_machine(__ftrace_modify_code, &command, NULL);
 }
 
+#ifdef CONFIG_OLD_MCOUNT
+#define OLD_MCOUNT_ADDR	((unsigned long) mcount)
+#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
+
+#define	OLD_NOP		0xe1a00000	/* mov r0, r0 */
+
 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
 {
 	return rec->arch.old_mcount ? OLD_NOP : NOP;
-- 
2.7.4