linux-kernel - Re: [PATCH 06/25] x86/cpu/intel: Allow SGX virtualization without Launch Control support

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Date:   Mon, 8 Mar 2021 12:50:26 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, seanjc@...gle.com, jarkko@...nel.org,
        luto@...nel.org, dave.hansen@...el.com, rick.p.edgecombe@...el.com,
        haitao.huang@...el.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, jethro@...tanix.com,
        b.thiel@...teo.de
Subject: Re: [PATCH 06/25] x86/cpu/intel: Allow SGX virtualization without
 Launch Control support

On Fri, 5 Mar 2021 18:29:57 +0100 Borislav Petkov wrote:
> On Mon, Mar 01, 2021 at 10:45:02PM +1300, Kai Huang wrote:
> > From: Sean Christopherson <sean.j.christopherson@...el.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@...el.com>
> > Co-developed-by: Kai Huang <kai.huang@...el.com>
> > Acked-by: Dave Hansen <dave.hansen@...el.com>
> > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > ---
> >  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;
> 
> The preferred ordering of variable declarations at the beginning of a
> function is reverse fir tree order::
> 
> 	struct long_struct_name *descriptive_name;
> 	unsigned long foo, bar;
> 	unsigned int tmp;
> 	int ret;
> 

Will do.

Since as you suggested, enable_sgx_any will be removed, and initializing
enable_sgx_driver/kvm will be moved into the if () statement, I think we should
explicitly initialize them here. How about below?

	bool enable_sgx_kvm = enable_sgx_driver = false;
	bool tboot = tboot_enabled();
	bool enable_vmx;
	...

> 
> >  	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);
> > +
> >  	/*
> > -	 * 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);
> 
> That enable_sgx_any use looks weird. You can get rid of it:
> 
> 	if (cpu_has(c, X86_FEATURE_SGX) && IS_ENABLED(CONFIG_X86_SGX)) {
> 		enable_sgx_driver = cpu_has(c, X86_FEATURE_SGX_LC);
> 		enable_sgx_kvm    = enable_vmx && IS_ENABLED(CONFIG_X86_SGX_KVM);
> 	}
> 
> and yap, let longer lines stick out.

Thanks. Will do.

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette