linux-kernel - Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

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Message-Id: <C11C9312-65BC-460A-8F9F-608E101AE5C1@amacapital.net>
Date:   Tue, 27 Nov 2018 09:55:45 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     "Dr. Greg" <greg@...ellic.com>, Andy Lutomirski <luto@...nel.org>,
        X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-sgx@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        nhorman@...hat.com, npmccallum@...hat.com,
        "Ayoun, Serge" <serge.ayoun@...el.com>, shay.katz-zamir@...el.com,
        haitao.huang@...ux.intel.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Svahn, Kai" <kai.svahn@...el.com>, mark.shanahan@...el.com,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver



> On Nov 27, 2018, at 8:41 AM, Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:
> 
>> On Tue, Nov 27, 2018 at 02:55:33AM -0600, Dr. Greg wrote:
>> Since the thread has become a bit divergent I wanted to note that we
>> have offered a proposal for a general policy management framework
>> based on MRSIGNER values.  This framework is consistent with the SGX
>> security model, ie. cryptographic rather then DAC based policy
>> controls.  This framework also allows a much more flexible policy
>> implementation that doesn't result in combinatoric issues.
>> 
>> Our framework also allows the preservation of the current ABI which
>> allows an EINITTOKEN to be passed in from userspace.  The framework
>> also supports the ability to specify that only a kernel based launch
>> enclave (LE) should be available if the platform owner or distribution
>> should desire to implement such a model.
>> 
>> The policy management framework is straight forward.  Three linked
>> lists or their equivalent which are populated through /sysfs
>> pseudo-files or equivalent plumbing.  Each list is populated with
>> MRSIGNER values for signing keys that are allowed to initialize
>> enclaves under three separate conditions.
>> 
>> 1.) General enclaves without special attribute bits.
>> 
>> 2.) Enclaves with the SGX_FLAGS_PROVISION_KEY attribute set. - i.e.,
>> 'Provisioning Enclaves'.
>> 
>> 3.) Enclaves with the SGX_FLAGS_LICENSE_KEY attribute set - i.e., 'Launch
>> Enclaves'.
>> 
>> An all-null MRSIGNER value serves as a 'sealing' value that locks a
>> list from any further modifications.
>> 
>> This architecture allows platform policies to be specified and then
>> sealed at early boot by the root user.  At that point cryptographic
>> policy controls are in place rather then DAC based controls, the
>> latter of which have perpetual security liabilities in addition to the
>> useability constraints inherent in a DAC or device node model.
>> 
>> We have developed an independent implementation of the PSW and
>> arguably have as much experience with issues surrounding how to
>> interact with the device driver as anyone.  We have spent a lot of
>> time thinking about these issues and the above framework provides the
>> most flexible architecture available.
> 
> Sounds like a lot bloat and policy added to the kernel whereas with
> Andy's proposal you can implement logic to a daemon and provide only
> mechanism to do it.
> 
> 

Well, almost. We’d need SGX_IOC_FREEZE_MR{ENCLAVE,SIGNER} or similar.  Or maybe the daemon could handle the entire loading process.  But this can wait until after the main driver is upstream.

This does lead to a question: enclaves are kind-of-sort-of mapped into a given address space. What happens if you issue the various ioctls in the context of a different mm?  For that matter, can two processes mmap the same enclave?