linux-kernel - Re: [RFC v4 03/17] x86: key creation with PKEY_DISABLE

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Date:   Tue, 27 Jun 2017 21:32:12 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        dave.hansen@...el.com, hbabu@...ibm.com, arnd@...db.de,
        akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v4 03/17] x86: key creation with PKEY_DISABLE_EXECUTE
 disallowed

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@...ibm.com>
> ---
>  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@...il.com>

Balbir Singh.