linux-kernel - Re: [PATCH v11 07/13] x86, sgx: detect Intel SGX

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Date:   Tue, 19 Jun 2018 16:33:43 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        sean.j.christopherson@...el.com, nhorman@...hat.com,
        npmccallum@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>,
        "open list:INTEL SGX" <intel-sgx-kernel-dev@...ts.01.org>
Subject: Re: [PATCH v11 07/13] x86, sgx: detect Intel SGX

On Fri, Jun 08, 2018 at 10:36:14AM -0700, Dave Hansen wrote:
> > +config INTEL_SGX_CORE
> > +	prompt "Intel SGX core functionality
> > +	depends on X86_64 && CPU_SUP_INTEL
> > +	help
> > +	Intel Software Guard eXtensions (SGX) is a set of CPU instructions
> > +	that allows ring 3 applications to create enclaves; private regions
> > +	of memory that are protected, by hardware, from unauthorized access
> > +	and/or modification.
> 
> That semicolon needs to be a colon.  The second half of that sentence is
> not a stand-alone statement.
> 
> > +	This option enables kernel recognition of SGX, high-level management
> > +	of the Enclave Page Cache (EPC), tracking and writing of SGX Launch
> > +	Enclave Hash MSRs, and allows for virtualization of SGX via KVM. By
> > +	iteslf, this option does not provide SGX support to userspace.
> > +
> > +	For details, see Documentation/x86/intel_sgx.rst
> > +
> > +	If unsure, say N.
> > +
> >  config EFI
> >  	bool "EFI runtime service support"
> >  	depends on ACPI
> > diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> > new file mode 100644
> > index 000000000000..fa3e6e0eb8af
> > --- /dev/null
> > +++ b/arch/x86/include/asm/sgx.h
> > @@ -0,0 +1,25 @@
> > +// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
> > +// Copyright(c) 2016-18 Intel Corporation.
> > +//
> > +// Authors:
> > +//
> > +// Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > +// Suresh Siddha <suresh.b.siddha@...el.com>
> > +// Sean Christopherson <sean.j.christopherson@...el.com>
> > +
> > +#ifndef _ASM_X86_SGX_H
> > +#define _ASM_X86_SGX_H
> > +
> > +#include <linux/types.h>
> > +
> > +#define SGX_CPUID 0x12
> 
> Hey, I just saw 0x12 as a magic, hard-coded number earlier in these
> patches.  It seems cruel to hard-code it, and then also have a #define
> that isn't used.

It i then is a regression in the series. I'll fix it.

> > +enum sgx_cpuid {
> > +	SGX_CPUID_CAPABILITIES	= 0,
> > +	SGX_CPUID_ATTRIBUTES	= 1,
> > +	SGX_CPUID_EPC_BANKS	= 2,
> > +};
> 
> These are cpuid *leaves*, right?  Please make this clear that these are
> hardware-defined values and not some kind of software construct.
> 
> > +bool sgx_enabled __ro_after_init = false;
> > +EXPORT_SYMBOL(sgx_enabled);
> > +
> > +static __init bool sgx_is_enabled(void)
> > +{
> > +	unsigned long fc;
> > +
> > +	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
> > +		return false;
> 
> Not necessary. CPUID does this part for you.
> 
> > +	if (!boot_cpu_has(X86_FEATURE_SGX))
> > +		return false;
> > +
> > +	if (!boot_cpu_has(X86_FEATURE_SGX1))
> > +		return false;
> > +
> > +	rdmsrl(MSR_IA32_FEATURE_CONTROL, fc);
> > +	if (!(fc & FEATURE_CONTROL_LOCKED))
> > +		return false;
> > +
> > +	if (!(fc & FEATURE_CONTROL_SGX_ENABLE))
> > +		return false;
> 
> Comments, please.  Why would this happen?  What would it mean?

Thanks for the feedback! I'll refine the parts that you pointed out.

/Jarkko