Re: [PATCH v6 03/11] x86: define IA32_FEATURE_CONTROL.SGX_ENABLE

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Sat, 2017-11-25 at 21:29 +0200, Jarkko Sakkinen wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
> 
> When IA32_FEATURE_CONTROL.SGX_ENABLE and IA32_FEATURE_CONTROL.LOCK are
> set by the pre-boot firmware, SGX is usable by the OS.

This implies that only pre-boot firmware can write feature control, which is not
true.  What about:

    SGX instructions (ENCLS and ENCLU) are usable if and only if SGX_ENABLE is
    set in the IA32_FEATURE_CONTROL MSR and said MSR is locked.

> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> ---
>  arch/x86/include/asm/msr-index.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-
> index.h
> index 17f5c12e1afd..b35cb98b5d60 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -435,6 +435,7 @@
>  #define FEATURE_CONTROL_LOCKED				(1<<0)
>  #define FEATURE_CONTROL_VMXON_ENABLED_INSIDE_SMX	(1<<1)
>  #define FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX	(1<<2)
> +#define FEATURE_CONTROL_SGX_ENABLE                      (1<<18)
>  #define FEATURE_CONTROL_LMCE				(1<<20)
>  
>  #define MSR_IA32_APICBASE		0x0000001b