Re: [PATCH v26 10/22] x86/sgx: Linux Enclave Driver

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Andy Lutomirski <luto@amacapital.net>
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>
Subject: Re: [PATCH v26 10/22] x86/sgx: Linux Enclave Driver
Date: Fri, 14 Feb 2020 09:52:11 -0800	[thread overview]
Message-ID: <20200214175211.GE20690@linux.intel.com> (raw)
In-Reply-To: <D18DD438-2458-4264-9D56-A05EB84BB545@amacapital.net>

On Fri, Feb 14, 2020 at 09:40:00AM -0800, Andy Lutomirski wrote:
> 
> 
> > On Feb 14, 2020, at 9:11 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> > 
> > On 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;
> >>>>> +};
> >>>> 
> >>>> 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.
> >>> 
> >>> Why is it not acceptable?  E.g. what specific use case do you have that
> >>> _requires_ on measuring partial 4k pages of an enclave?
> >> 
> >> 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 be
> >> different, and it won't work.
> > 
> > And if our ABI says "thou shall measure in 4k chunks", then it's an invalid
> > enclave if its author generated MRENCLAVE using a different granularity.
> 
> ISTM, unless there’s a particularly compelling reason, if an enclave is
> valid, we should be able to load it.

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].

I think we'd still want to keep the MEASURE flag for SGX_IOC_ENCLAVE_ADD_PAGE
so that we can optimize EADD[0]->EEXTEND[0]->EADD[1]->EEXTEND[1].