Re: [RFC v4 03/17] x86: key creation with PKEY_DISABLE_EXECUTE disallowed

[Balbir Singh]

On Tue, 2017-06-27 at 03:11 -0700, Ram Pai wrote:
> x86 does not support disabling execute permissions on a pkey.
> 
> Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
> ---
>  arch/x86/kernel/fpu/xstate.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index c24ac1e..d582631 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -900,6 +900,9 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
>  	if (!boot_cpu_has(X86_FEATURE_OSPKE))
>  		return -EINVAL;
>  
> +	if (init_val & PKEY_DISABLE_EXECUTE)
> +		return -EINVAL;
> +
>  	/* Set the bits we need in PKRU:  */
>  	if (init_val & PKEY_DISABLE_ACCESS)
>  		new_pkru_bits |= PKRU_AD_BIT;

I am not an x86 expert. IIUC, execute disable is done via allocating an
execute_only_pkey and checking vma_key via AD + vma_flags against VM_EXEC.

Your patch looks good to me

Acked-by: Balbir Singh <bsingharora@xxxxxxxxx>

Balbir Singh.