Re: [RFC PATCH v3 07/27] x86/cpu/intel: Allow SGX virtualization without Launch Control support

[Sean Christopherson <seanjc@google.com>]

On Tue, Jan 26, 2021, Dave Hansen wrote:
> > -	enable_sgx = cpu_has(c, X86_FEATURE_SGX) &&
> > -		     cpu_has(c, X86_FEATURE_SGX_LC) &&
> > -		     IS_ENABLED(CONFIG_X86_SGX);
> > +	enable_sgx_any = cpu_has(c, X86_FEATURE_SGX) &&
> > +			 cpu_has(c, X86_FEATURE_SGX1) &&
> > +			 IS_ENABLED(CONFIG_X86_SGX);
> 
> The X86_FEATURE_SGX1 check seems to have snuck in here.  Why?

It's a best effort check to handle the scenario where SGX is enabled by BIOS,
but was disabled by hardware in response to a machine check bank being disabled.
Adding a check on SGX1 should be in a different patch.  I thought we had a
dicscussion about why the check was omitted in the merge of bare metal support,
but I can't find any such thread.

> > +	enable_sgx_driver = enable_sgx_any &&
> > +			    cpu_has(c, X86_FEATURE_SGX_LC);
> > +	enable_sgx_kvm = enable_sgx_any && enable_vmx &&
> > +			  IS_ENABLED(CONFIG_X86_SGX_KVM);
> >  
> >  	if (msr & FEAT_CTL_LOCKED)
> >  		goto update_caps;
> > @@ -136,15 +146,18 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
> >  	 * i.e. KVM is enabled, to avoid unnecessarily adding an attack vector
> >  	 * for the kernel, e.g. using VMX to hide malicious code.
> >  	 */
> > -	if (cpu_has(c, X86_FEATURE_VMX) && IS_ENABLED(CONFIG_KVM_INTEL)) {
> > +	if (enable_vmx) {
> >  		msr |= FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX;
> >  
> >  		if (tboot)
> >  			msr |= FEAT_CTL_VMX_ENABLED_INSIDE_SMX;
> >  	}
> >  
> > -	if (enable_sgx)
> > -		msr |= FEAT_CTL_SGX_ENABLED | FEAT_CTL_SGX_LC_ENABLED;
> > +	if (enable_sgx_kvm || enable_sgx_driver) {
> > +		msr |= FEAT_CTL_SGX_ENABLED;
> > +		if (enable_sgx_driver)
> > +			msr |= FEAT_CTL_SGX_LC_ENABLED;
> > +	}
> >  
> >  	wrmsrl(MSR_IA32_FEAT_CTL, msr);
> >  
> > @@ -167,10 +180,29 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
> >  	}
> >  
> >  update_sgx:
> > -	if (!(msr & FEAT_CTL_SGX_ENABLED) ||
> > -	    !(msr & FEAT_CTL_SGX_LC_ENABLED) || !enable_sgx) {
> > -		if (enable_sgx)
> > -			pr_err_once("SGX disabled by BIOS\n");
> > +	if (!(msr & FEAT_CTL_SGX_ENABLED)) {
> > +		if (enable_sgx_kvm || enable_sgx_driver)
> > +			pr_err_once("SGX disabled by BIOS.\n");
> >  		clear_cpu_cap(c, X86_FEATURE_SGX);
> > +		return;
> > +	}
> 
> 
> Isn't there a pr_fmt here already?  Won't these just look like:
> 
> 	sgx: SGX disabled by BIOS.
> 
> That seems a bit silly.

Eh, I like the explicit "SGX" to clarify that the hardware feature was disabled.