[PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[Mithil Bavishi]

With CONFIG_CFI enabled, OMAP4 can trap in omap4_enter_lowpower()
because omap_pm_ops.finish_suspend points directly to the assembly
routine omap4_finish_suspend, which lacks the expected KCFI type
metadata.

Add a small C wrapper with the exact callback prototype and use it for
finish_suspend.

Signed-off-by: Mithil Bavishi <bavishimithil@gmail.com>
---
 arch/arm/mach-omap2/omap-mpuss-lowpower.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-omap2/omap-mpuss-lowpower.c b/arch/arm/mach-omap2/omap-mpuss-lowpower.c
index f18ef45e2..1c51b2f97 100644
--- a/arch/arm/mach-omap2/omap-mpuss-lowpower.c
+++ b/arch/arm/mach-omap2/omap-mpuss-lowpower.c
@@ -111,6 +111,11 @@ static struct cpu_pm_ops omap_pm_ops = {
 	.hotplug_restart	= dummy_cpu_resume,
 };
 
+static int omap4_finish_suspend_wrapper(unsigned long cpu_state)
+{
+	return omap4_finish_suspend(cpu_state);
+}
+
 /*
  * Program the wakeup routine address for the CPU0 and CPU1
  * used for OFF or DORMANT wakeup.
@@ -437,7 +442,7 @@ int __init omap4_mpuss_init(void)
 	}
 
 	if (cpu_is_omap44xx()) {
-		omap_pm_ops.finish_suspend = omap4_finish_suspend;
+		omap_pm_ops.finish_suspend = omap4_finish_suspend_wrapper;
 		omap_pm_ops.resume = omap4_cpu_resume;
 		omap_pm_ops.scu_prepare = scu_pwrst_prepare;
 		omap_pm_ops.hotplug_restart = omap4_secondary_startup;
-- 
2.43.0

Re: [PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[Nathan Chancellor]

On Tue, May 12, 2026 at 12:23:41AM -0400, Mithil Bavishi wrote:
> With CONFIG_CFI enabled, OMAP4 can trap in omap4_enter_lowpower()
> because omap_pm_ops.finish_suspend points directly to the assembly
> routine omap4_finish_suspend, which lacks the expected KCFI type
> metadata.

It sounds like omap4_finish_suspend() should be defined with
SYM_TYPED_FUNC_START then? Is that the case for all of the other
functions that are added to omap_pm_ops?

> Add a small C wrapper with the exact callback prototype and use it for
> finish_suspend.
> 
> Signed-off-by: Mithil Bavishi <bavishimithil@gmail.com>
> ---
>  arch/arm/mach-omap2/omap-mpuss-lowpower.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-omap2/omap-mpuss-lowpower.c b/arch/arm/mach-omap2/omap-mpuss-lowpower.c
> index f18ef45e2..1c51b2f97 100644
> --- a/arch/arm/mach-omap2/omap-mpuss-lowpower.c
> +++ b/arch/arm/mach-omap2/omap-mpuss-lowpower.c
> @@ -111,6 +111,11 @@ static struct cpu_pm_ops omap_pm_ops = {
>  	.hotplug_restart	= dummy_cpu_resume,
>  };
>  
> +static int omap4_finish_suspend_wrapper(unsigned long cpu_state)
> +{
> +	return omap4_finish_suspend(cpu_state);
> +}
> +
>  /*
>   * Program the wakeup routine address for the CPU0 and CPU1
>   * used for OFF or DORMANT wakeup.
> @@ -437,7 +442,7 @@ int __init omap4_mpuss_init(void)
>  	}
>  
>  	if (cpu_is_omap44xx()) {
> -		omap_pm_ops.finish_suspend = omap4_finish_suspend;
> +		omap_pm_ops.finish_suspend = omap4_finish_suspend_wrapper;
>  		omap_pm_ops.resume = omap4_cpu_resume;
>  		omap_pm_ops.scu_prepare = scu_pwrst_prepare;
>  		omap_pm_ops.hotplug_restart = omap4_secondary_startup;
> -- 
> 2.43.0
> 

-- 
Cheers,
Nathan

Re: [PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[Andreas Kemnade]

On Tue, 12 May 2026 16:34:42 +0900
Nathan Chancellor <nathan@kernel.org> wrote:

> On Tue, May 12, 2026 at 12:23:41AM -0400, Mithil Bavishi wrote:
> > With CONFIG_CFI enabled, OMAP4 can trap in omap4_enter_lowpower()
> > because omap_pm_ops.finish_suspend points directly to the assembly
> > routine omap4_finish_suspend, which lacks the expected KCFI type
> > metadata.  
> 
> It sounds like omap4_finish_suspend() should be defined with
> SYM_TYPED_FUNC_START then? Is that the case for all of the other
> functions that are added to omap_pm_ops?
> 
omap_cpu_resume: the address is written to some cpu register and
on that way casted to u32. So therefore does not trigger CFI.
Same for secondary_startup which is also assembler code.
scu_prepare is C.

DO you have a pointer to any documentation:
:~/linux$ grep -R SYM_TYPED_FUNC_START Documentation/

Regards,
Andreas

Re: [PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[Nathan Chancellor]

On Tue, May 12, 2026 at 10:02:07AM +0200, Andreas Kemnade wrote:
> On Tue, 12 May 2026 16:34:42 +0900
> Nathan Chancellor <nathan@kernel.org> wrote:
> 
> > On Tue, May 12, 2026 at 12:23:41AM -0400, Mithil Bavishi wrote:
> > > With CONFIG_CFI enabled, OMAP4 can trap in omap4_enter_lowpower()
> > > because omap_pm_ops.finish_suspend points directly to the assembly
> > > routine omap4_finish_suspend, which lacks the expected KCFI type
> > > metadata.  
> > 
> > It sounds like omap4_finish_suspend() should be defined with
> > SYM_TYPED_FUNC_START then? Is that the case for all of the other
> > functions that are added to omap_pm_ops?
> > 
> omap_cpu_resume: the address is written to some cpu register and
> on that way casted to u32. So therefore does not trigger CFI.
> Same for secondary_startup which is also assembler code.
> scu_prepare is C.
> 
> DO you have a pointer to any documentation:
> :~/linux$ grep -R SYM_TYPED_FUNC_START Documentation/

I don't think we have any formal documentation for SYM_TYPED_FUNC_START
(it should probably be documented via kernel-doc?) but you can read the
commit message of the change that added it for more information:

  e84e008e7b02 ("cfi: Add type helper macros")

-- 
Cheers,
Nathan

Re: [PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[Mithil Bavishi]

> I don't think we have any formal documentation for SYM_TYPED_FUNC_START
> (it should probably be documented via kernel-doc?) but you can read the
> commit message of the change that added it for more information:
>
>  e84e008e7b02 ("cfi: Add type helper macros")

Thanks, I had a look at it and other similar commits like

c50d328 ("arm64: Add types to indirect called assembly functions")

I was not aware of SYM_TYPED_FUNC_START before hence the logical approach
was just to wrap the function. But now with this I'll send a v2 with the
ENTRY and ENDPROC changed to SYM_TYPED_FUNC_START and SYM_FUNC_END.

Best,
Mithil

Re: [PATCH] ARM: OMAP2+: Make OMAP4 finish_suspend callback CFI-safe

[Andreas Kemnade]

On Tue, 12 May 2026 22:57:57 +0900
Nathan Chancellor <nathan@kernel.org> wrote:

> On Tue, May 12, 2026 at 10:02:07AM +0200, Andreas Kemnade wrote:
> > On Tue, 12 May 2026 16:34:42 +0900
> > Nathan Chancellor <nathan@kernel.org> wrote:
> >   
> > > On Tue, May 12, 2026 at 12:23:41AM -0400, Mithil Bavishi wrote:  
> > > > With CONFIG_CFI enabled, OMAP4 can trap in omap4_enter_lowpower()
> > > > because omap_pm_ops.finish_suspend points directly to the assembly
> > > > routine omap4_finish_suspend, which lacks the expected KCFI type
> > > > metadata.    
> > > 
> > > It sounds like omap4_finish_suspend() should be defined with
> > > SYM_TYPED_FUNC_START then? Is that the case for all of the other
> > > functions that are added to omap_pm_ops?
> > >   
> > omap_cpu_resume: the address is written to some cpu register and
> > on that way casted to u32. So therefore does not trigger CFI.
> > Same for secondary_startup which is also assembler code.
> > scu_prepare is C.
> > 
> > DO you have a pointer to any documentation:
> > :~/linux$ grep -R SYM_TYPED_FUNC_START Documentation/  
> 
> I don't think we have any formal documentation for SYM_TYPED_FUNC_START
> (it should probably be documented via kernel-doc?) but you can read the
> commit message of the change that added it for more information:
> 
>   e84e008e7b02 ("cfi: Add type helper macros")
> 
Ok, I found what is the missing piece of the puzzle in my head:
"
In order to make this easier, the compiler emits a
    __kcfi_typeid_<function> symbol for each address-taken function
    declaration in C, which contains the expected type identifier that
    we can refer to in assembly code.
"
So time to look into my backyard if anything more is there.

Regards,
Andreas