Re: [RFC PATCH v5 06/26] x86/cpu/intel: Allow SGX virtualization without Launch Control support

Jarkko Sakkinen
2021-02-16T08:39:17Z

On Tue, Feb 16, 2021 at 05:03:26AM +0000, Huang, Kai wrote:
> >
> > On Sun, Feb 14, 2021 at 02:29:05AM +1300, Kai Huang wrote:
> > > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > >
> > > The kernel will currently disable all SGX support if the hardware does
> > > not support launch control. Make it more permissive to allow SGX
> > > virtualization on systems without Launch Control support. This will
> > > allow KVM to expose SGX to guests that have less-strict requirements
> > > on the availability of flexible launch control.
> > >
> > > Improve error message to distinguish between three cases. There are
> > > two cases where SGX support is completely disabled:
> > > 1) SGX has been disabled completely by the BIOS
> > > 2) SGX LC is locked by the BIOS. Bare-metal support is disabled because
> > > of LC unavailability. SGX virtualization is unavailable (because of
> > > Kconfig).
> > > One where it is partially available:
> > > 3) SGX LC is locked by the BIOS. Bare-metal support is disabled because
> > > of LC unavailability. SGX virtualization is supported.
> > >
> > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > > Co-developed-by: Kai Huang <kai.huang@intel.com>
> > > Signed-off-by: Kai Huang <kai.huang@intel.com>
> > > ---
> > > v4->v5:
> > >
> > > - No code change.
> > >
> > > v3->v4:
> > >
> > > - Removed cpu_has(X86_FEATURE_SGX1) check in enable_sgx_any, since it
> > logically
> > > is not related to KVM SGX series, per Sean.
> > > - Changed declaration of variables to be in reverse-christmas tree style, per
> > > Jarkko.
> > >
> > > v2->v3:
> > >
> > > - Added to use 'enable_sgx_any', per Dave.
> > > - Changed to call clear_cpu_cap() directly, rather than using clear_sgx_caps()
> > > and clear_sgx_lc().
> > > - Changed to use CONFIG_X86_SGX_KVM, instead of
> > CONFIG_X86_SGX_VIRTUALIZATION.
> > >
> > > v1->v2:
> > >
> > > - Refined commit message per Dave's comments.
> > > - Added check to only enable SGX virtualization when VMX is supported, per
> > > Dave's comment.
> > > - Refined error msg print to explicitly call out SGX virtualization will be
> > > supported when LC is locked by BIOS, per Dave's comment.
> > >
> > > ---
> > > arch/x86/kernel/cpu/feat_ctl.c | 57
> > > ++++++++++++++++++++++++++--------
> > > 1 file changed, 44 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/arch/x86/kernel/cpu/feat_ctl.c
> > > b/arch/x86/kernel/cpu/feat_ctl.c index 27533a6e04fa..96c370284913
> > > 100644
> > > --- a/arch/x86/kernel/cpu/feat_ctl.c
> > > +++ b/arch/x86/kernel/cpu/feat_ctl.c
> > > @@ -105,7 +105,8 @@ early_param("nosgx", nosgx); void
> > > init_ia32_feat_ctl(struct cpuinfo_x86 *c) {
> > > bool tboot = tboot_enabled();
> > > - bool enable_sgx;
> > > + bool enable_sgx_any, enable_sgx_kvm, enable_sgx_driver;
> > > + bool enable_vmx;
> > > u64 msr;
> > >
> > > if (rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr)) { @@ -114,13 +115,21
> > @@
> > > void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
> > > return;
> > > }
> > >
> > > + enable_vmx = cpu_has(c, X86_FEATURE_VMX) &&
> > > + IS_ENABLED(CONFIG_KVM_INTEL);
> >
> > It's less than 100 characters:
>
> Just carious, shouldn't be 80 characters to wrap a new line, instead of 100?

Try with checkpatch.pl.

>
> >
> > enable_vmx = cpu_has(c, X86_FEATURE_VMX) &&
> > IS_ENABLED(CONFIG_KVM_INTEL);
> >
> > This is better:
> >
> > enable_vmx = IS_ENABLED(CONFIG_KVM_INTEL) && cpu_has(c,
> > X86_FEATURE_VMX);
> >
> > You only want to evaluate cpu_has() if COHNFIG_KVM_INTEL is enabled.
>
> If you look at the original code, cpu_has() comes first. It's just one-time booting time code, and I don't think it matters.
>
> Btw, are you also suggesting IS_ENABLED(CONFIG_X86_SGX) should come before cpu_has() for SGX in below code?
>
> That being said, cpu_has() comes first for both VMX and SGX in the original code. I don't know why I need to change the sequence in this patch.
>
> >
> > > +
> > > /*
> > > - * Enable SGX if and only if the kernel supports SGX and Launch Control
> > > - * is supported, i.e. disable SGX if the LE hash MSRs can't be written.
> > > + * Separate out SGX driver enabling from KVM. This allows KVM
> > > + * guests to use SGX even if the kernel SGX driver refuses to
> > > + * use it. This happens if flexible Faunch Control is not
> > > + * available.
> > > */
> > > - 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) &&
> > > + IS_ENABLED(CONFIG_X86_SGX);
> > > + 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 +145,18 @@ 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 +179,29 @@ 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);
> >
> > Empty line before return statement.
>
> It's just two statements inside the if() {} statement. Putting a new line here is too sparse IMHO.
>
> I'd like to hear more.

This was a common review comment in original SGX series, so I'm
sticking to the pattern.

>
> Dave, do you have any comment?
>
> >
> > > + return;
> > > + }
> > > +
> > > + /*
> > > + * VMX feature bit may be cleared due to being disabled in BIOS,
> > > + * in which case SGX virtualization cannot be supported either.
> > > + */
> > > + if (!cpu_has(c, X86_FEATURE_VMX) && enable_sgx_kvm) {
> > > + pr_err_once("SGX virtualization disabled due to lack of VMX.\n");
> > > + enable_sgx_kvm = 0;
> > > + }
> > > +
> > > + if (!(msr & FEAT_CTL_SGX_LC_ENABLED) && enable_sgx_driver) {
> > > + if (!enable_sgx_kvm) {
> > > + pr_err_once("SGX Launch Control is locked. Disable
> > SGX.\n");
> > > + clear_cpu_cap(c, X86_FEATURE_SGX);
> > > + } else {
> > > + pr_err_once("SGX Launch Control is locked. Support
> > SGX virtualization only.\n");
> > > + clear_cpu_cap(c, X86_FEATURE_SGX_LC);
> > > + }
> > > }
> > > }
> > > --
> > > 2.29.2
> > >
> > >
> >
> > /Jarkko
>

/Jarkko