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

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Date:   Fri, 5 Mar 2021 18:29:57 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Kai Huang <kai.huang@...el.com>
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 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;


>  	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.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette