Subject: Re: [powerpc v6 2/3] Detect instruction fetch denied and report

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 16 Nov 2016 13:38:17 +0530

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()
>
> Signed-off-by: Balbir Singh <[email-masked]>
> ---
>  arch/powerpc/mm/fault.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index d0b137d..d498e40 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -390,6 +390,13 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  #endif /* CONFIG_8xx */
>  
>  	if (is_exec) {
> +
> +		/*
> +		 * An execution fault + no execute ?
> +		 */
> +		if (regs->msr & SRR1_ISI_N_OR_G)
> +			goto bad_area;
> +

Can we get that SRR1 value on cpu with  CPU_FTR_NOEXECUTE cleared ?
The comment below says, we should look at at VM_READ and VM_WRITE.

Also don't we need to look at user_mode(regs) here if we are moving this
above the vma check.

>  		/*
>  		 * Allow execution from readable areas if the MMU does not
>  		 * provide separate controls over reading and executing.
> @@ -404,6 +411,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  		    (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
>  		     !(vma->vm_flags & (VM_READ | VM_WRITE))))
>  			goto bad_area;
> +
>  #ifdef CONFIG_PPC_STD_MMU
>  		/*
>  		 * protfault should only happen due to us
> -- 
> 2.5.5