Subject: Re: [PATCH 2/2] Detect instruction fetch denied and report

From: Balbir Singh <[email-masked]>
Date: Mon, 22 Aug 2016 17:55:28 +1000

On Mon, Aug 22, 2016 at 11:35:36AM +0530, Aneesh Kumar K.V wrote:
> Balbir Singh <[email-masked]> writes:
> 
> > ISA 3 allows for prevention of instruction fetch and execution
> > of user mode pages. If such an error occurs, SRR1 bit 35
> > reports the error. We catch and report the error in do_page_fault()
> >
> 
> But what does the error mean ? A buggy application ? IIUC, it indicate a
> buggy kernel isn't it ?. So should we kill the application or panic() ?
>

We oops.. basically we get a kernel fault. We handle it the same way
we handle other kernel faults.
 
> 
> > Signed-off-by: Balbir Singh <[email-masked]>
> > ---
> >  arch/powerpc/mm/fault.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> > index a4db22f..f162e77 100644
> > --- a/arch/powerpc/mm/fault.c
> > +++ b/arch/powerpc/mm/fault.c
> > @@ -404,6 +404,10 @@ good_area:
> >  		    (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
> >  		     !(vma->vm_flags & (VM_READ | VM_WRITE))))
> >  			goto bad_area;
> > +#ifdef CONFIG_PPC_RADIX_MMU
> > +		if (radix_enabled() && regs->msr & PPC_BIT(35))
> > +			goto bad_area;
> > +#endif
> >  #ifdef CONFIG_PPC_STD_MMU
> >  		/*
> >  		 * protfault should only happen due to us
> 
> -aneesh
>