From mboxrd@z Thu Jan  1 00:00:00 1970
From: rostedt@goodmis.org (Steven Rostedt)
Date: Wed, 20 Jun 2018 21:29:06 -0400
Subject: Dynamic ftrace self test broken on ARM
In-Reply-To: <20180620230734.GO17671@n2100.armlinux.org.uk>
References: <65fb14b356bc0a414f1fe5cf5c6eb395@agner.ch>
 <20180618175437.3e6c85a1@gandalf.local.home>
 <b9f269ed2143688c38cdcbba7367b101@agner.ch>
 <20180619091735.7aec75d0@gandalf.local.home>
 <5e26cebbb2ebeb87fdc808509881736b@agner.ch>
 <20180620101311.0bcd73d3@gandalf.local.home>
 <7904ed3fe9f59a54526d64f366915b43@agner.ch>
 <e4181ae694d44913a8eba4618477bd3b@agner.ch>
 <ac0178fb75658a8d7d7b1931691c7755@agner.ch>
 <20180620230734.GO17671@n2100.armlinux.org.uk>
Message-ID: <20180620212906.24b7b66e@vmware.local.home>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, 21 Jun 2018 00:07:34 +0100
Russell King - ARM Linux <linux@armlinux.org.uk> wrote:


> > Any input from ARM folks?  
> 
> The same issues must exist on other architectures as ARM is not the only
> architecture to implement read-only kernel text and dynamic ftrace, so
> surely this problem isn't unique to ARM.

Probably because of the way set_kernel_text_ro() is implemented in
other archs. For example, in x86, we have:

void set_kernel_text_ro(void)
{
	unsigned long start = PFN_ALIGN(_text);
	unsigned long end = PFN_ALIGN(__stop___ex_table);

	if (!kernel_set_to_readonly)
		return;

	/*
	 * Set the kernel identity mapping for text RO.
	 */
	set_memory_ro(start, (end - start) >> PAGE_SHIFT);
}

and arm has:

void set_kernel_text_ro(void)
{
	set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
				current->active_mm);
}

Where x86's set_kernel_text_ro() is a nop until the
kernel_set_to_readonly is set.

Perhaps this may fix things?

[ Not even compiled tested ]

-- Steve

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index c186474422f3..0cc8e04295a4 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -736,20 +736,29 @@ static int __mark_rodata_ro(void *unused)
 	return 0;
 }
 
+static int kernel_set_to_readonly __read_mostly;
+
 void mark_rodata_ro(void)
 {
+	kernel_set_to_readonly = 1;
 	stop_machine(__mark_rodata_ro, NULL, NULL);
 	debug_checkwx();
 }
 
 void set_kernel_text_rw(void)
 {
+	if (!kernel_set_to_readonly)
+		return;
+
 	set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), false,
 				current->active_mm);
 }
 
 void set_kernel_text_ro(void)
 {
+	if (!kernel_set_to_readonly)
+		return;
+
 	set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
 				current->active_mm);
 }