linux-kernel - Re: [PATCH v39 15/24] x86/sgx: Add SGX_IOC_ENCLAVE

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Date:   Sat, 24 Oct 2020 14:40:04 +0300
From:   Jarkko Sakkinen <kernel.org@...nel.org>
To:     Jethro Beekman <jethro@...tanix.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Darren Kenny <darren.kenny@...cle.com>,
        Andy Lutomirski <luto@...nel.org>, akpm@...ux-foundation.org,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com, bp@...en8.de,
        cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        haitao.huang@...el.com, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, nhorman@...hat.com,
        npmccallum@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        sean.j.christopherson@...el.com, tglx@...utronix.de,
        yaozhangx@...gle.com, mikko.ylinen@...el.com
Subject: Re: [PATCH v39 15/24] x86/sgx: Add SGX_IOC_ENCLAVE_PROVISION

On Fri, Oct 23, 2020 at 04:23:55PM +0200, Jethro Beekman wrote:
> On 2020-10-23 12:17, Jarkko Sakkinen wrote:
> > On Tue, Oct 20, 2020 at 02:19:26PM -0700, Dave Hansen wrote:
> >> On 10/2/20 9:50 PM, Jarkko Sakkinen wrote:
> >>> + * Failure to explicitly request access to a restricted attribute will cause
> >>> + * sgx_ioc_enclave_init() to fail.  Currently, the only restricted attribute
> >>> + * is access to the PROVISION_KEY.
> >>
> >> Could we also justify why access is restricted, please?  Maybe:
> >>
> >> 	Access is restricted because PROVISION_KEY is burned uniquely
> >> 	into each each processor, making it a perfect unique identifier
> >> 	with privacy and fingerprinting implications.
> >>
> >> Are there any other reasons for doing it this way?
> > 
> > AFAIK, if I interperet the SDM correctl, PROVISION_KEY and
> > PROVISION_SEALING_KEY also have random salt added, i.e. they change
> > every boot cycle.
> > 
> > There is "RAND = yes" on those keys in Table 40-64 of Intel SDM volume
> > 3D :-)
> > 
> 
> This is nonsense. The whole point of sealing keys is that they don't
> change every boot. If did they they'd have no value over enclave
> memory. RAND means that the KEYID field from the KEYREQUEST is
> included in the derivation (as noted in the source row of the table
> you looked at).

I just looked that the column name is RAND, the row is called "Provision
key" and the cell has "Yes" in it.

> --
> Jethro Beekman | Fortanix

/Jarkko