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

[Andreas Kemnade <andreas@kemnade.info>]

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