[PATCH v4 1/2] arm64: Support execute-only permissions with Enhanced PAN

[Catalin Marinas]

On Fri, Mar 12, 2021 at 05:38:10PM +0000, Vladimir Murzin wrote:
> @@ -992,6 +995,18 @@ static inline bool arch_wants_old_prefaulted_pte(void)
>  }
>  #define arch_wants_old_prefaulted_pte	arch_wants_old_prefaulted_pte
>  
> +static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
> +{
> +	if (cpus_have_const_cap(ARM64_HAS_EPAN))
> +		return prot;
> +
> +	if (pgprot_val(prot) != pgprot_val(PAGE_EXECONLY))
> +		return prot;
> +
> +	return PAGE_READONLY_EXEC;
> +}

Just a thought: we could allow exec-only permissions if
!system_uses_hw_pan(), though not sure it's worth it. We'd have 8.0 CPUs
with exec-only then a gap up to 8.7 when we add it back in (since most
kernels will turn PAN on).

-- 
Catalin