Dynamic ftrace self test broken on ARM

Commit Message

Steven Rostedt June 21, 2018, 1:29 a.m. UTC

On Thu, 21 Jun 2018 00:07:34 +0100
Russell King - ARM Linux <[e-mail]> 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

Comments

Stefan Agner June 21, 2018, 7:25 a.m. UTC | #1

On 21.06.2018 03:29, Steven Rostedt wrote:
> On Thu, 21 Jun 2018 00:07:34 +0100
> Russell King - ARM Linux <[e-mail]> 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);
>  }

This aligns nicely with how this has been solved with commit
162396309745 ("ftrace, x86: make kernel text writable only for
conversions") a while ago.
Reviewed-by: Stefan Agner <[e-mail]>

Compiled and tested here, selftest as well as ftrace at runtime seems to
work fine.
Tested-by: Stefan Agner <[e-mail]>

Thanks Steven! Can you send a patch or should I do it?

--
Stefan

Steven Rostedt June 21, 2018, 1:51 p.m. UTC | #2

On Thu, 21 Jun 2018 09:25:48 +0200
Stefan Agner <[e-mail]> wrote:


> This aligns nicely with how this has been solved with commit
> 162396309745 ("ftrace, x86: make kernel text writable only for
> conversions") a while ago.
> Reviewed-by: Stefan Agner <[e-mail]>
> 
> Compiled and tested here, selftest as well as ftrace at runtime seems to
> work fine.
> Tested-by: Stefan Agner <[e-mail]>
> 
> Thanks Steven! Can you send a patch or should I do it?

I'll resend a proper patch. Thanks for looking into it!

-- Steve

Patch

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);
 }