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

Sean Christopherson
2021-01-27T10:19:59Z

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.