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From:   Andy Lutomirski <luto@amacapital.net>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH v26 10/22] x86/sgx: Linux Enclave Driver
Date:   Sat, 15 Feb 2020 08:56:54 -0800
Message-Id: <033BCE0D-FA8C-40FB-849A-E401A5C6F6A3@amacapital.net>
References: <20200214175211.GE20690@linux.intel.com>
Cc:     Jethro Beekman <jethro@fortanix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
        dave.hansen@intel.com, nhorman@redhat.com, npmccallum@redhat.com,
        haitao.huang@intel.com, andriy.shevchenko@linux.intel.com,
        tglx@linutronix.de, kai.svahn@intel.com, bp@alien8.de,
        josh@joshtriplett.org, luto@kernel.org, kai.huang@intel.com,
        rientjes@google.com, cedric.xing@intel.com, puiterwijk@redhat.com,
        linux-security-module@vger.kernel.org,
        Haitao Huang <haitao.huang@linux.intel.com>
In-Reply-To: <20200214175211.GE20690@linux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Feb 14, 2020, at 9:52 AM, Sean Christopherson <sean.j.christopherson@in=
tel.com> wrote:
>=20
> =EF=BB=BFOn Fri, Feb 14, 2020 at 09:40:00AM -0800, Andy Lutomirski wrote:
>>=20
>>=20
>>>> On Feb 14, 2020, at 9:11 AM, Sean Christopherson <sean.j.christopherson=
@intel.com> wrote:
>>>=20
>>> =EF=BB=BFOn Fri, Feb 14, 2020 at 10:24:10AM +0100, Jethro Beekman wrote:=

>>>>> On 2020-02-13 19:07, Sean Christopherson wrote:
>>>>> On Thu, Feb 13, 2020 at 02:59:52PM +0100, Jethro Beekman wrote:
>>>>>> On 2020-02-09 22:25, Jarkko Sakkinen wrote:
>>>>>>> +/**
>>>>>>> + * struct sgx_enclave_add_pages - parameter structure for the
>>>>>>> + *                                %SGX_IOC_ENCLAVE_ADD_PAGE ioctl
>>>>>>> + * @src:    start address for the page data
>>>>>>> + * @offset:    starting page offset
>>>>>>> + * @length:    length of the data (multiple of the page size)
>>>>>>> + * @secinfo:    address for the SECINFO data
>>>>>>> + * @flags:    page control flags
>>>>>>> + * @count:    number of bytes added (multiple of the page size)
>>>>>>> + */
>>>>>>> +struct sgx_enclave_add_pages {
>>>>>>> +    __u64    src;
>>>>>>> +    __u64    offset;
>>>>>>> +    __u64    length;
>>>>>>> +    __u64    secinfo;
>>>>>>> +    __u64    flags;
>>>>>>> +    __u64    count;
>>>>>>> +};
>>>>>>=20
>>>>>> Compared to the last time I looked at the patch set, this API removes=
 the
>>>>>> ability to measure individual pages chunks. That is not acceptable.
>>>>>=20
>>>>> Why is it not acceptable?  E.g. what specific use case do you have tha=
t
>>>>> _requires_ on measuring partial 4k pages of an enclave?
>>>>=20
>>>> The use case is someone gives me an enclave and I want to load it. If I=
 don't
>>>> load it exactly as the enclave author specified, the enclave hash will b=
e
>>>> different, and it won't work.
>>>=20
>>> And if our ABI says "thou shall measure in 4k chunks", then it's an inva=
lid
>>> enclave if its author generated MRENCLAVE using a different granularity.=

>>=20
>> ISTM, unless there=E2=80=99s a particularly compelling reason, if an encl=
ave is
>> valid, we should be able to load it.
>=20
> That means we have to have a separate ioctl() for EEXTEND, otherwise we
> can't handle EADD[0]->EADD[1]->EADD[2]->EEXTEND[0]->EEXTEND[1]->EEXTEND[2]=
.
>=20
> I think we'd still want to keep the MEASURE flag for SGX_IOC_ENCLAVE_ADD_P=
AGE
> so that we can optimize EADD[0]->EEXTEND[0]->EADD[1]->EEXTEND[1].

Seems reasonable to me. I suppose such as ioctl could also be added later if=
 there=E2=80=99s a need.=