Re: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing shadow stack

[Dave Hansen]

On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

This still needs a changelog, even if you think it's simple.
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -446,6 +446,15 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
>  	error = -ENOMEM;
>  	if (!vma)
>  		goto out;
> +
> +	/*
> +	 * Do not allow changing shadow stack memory.
> +	 */
> +	if (vma->vm_flags & VM_SHSTK) {
> +		error = -EINVAL;
> +		goto out;
> +	}
> +

I think this is a _bit_ draconian.  Why shouldn't we be able to use
protection keys with a shadow stack?  Or, set it to PROT_NONE?