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

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 22 Aug 2016 11:35:36 +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()
>

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() ?

> 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