linux-kernel - RE: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page permissions

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Date:   Mon, 28 Feb 2022 17:44:20 +0000
From:   "Dhanraj, Vijay" <vijay.dhanraj@...el.com>
To:     "Hansen, Dave" <dave.hansen@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
CC:     "Chatre, Reinette" <reinette.chatre@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...en8.de" <bp@...en8.de>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Zhang, Cathy" <cathy.zhang@...el.com>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "Shanahan, Mark" <mark.shanahan@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page
 permissions

> On 2/28/22 04:24, Jarkko Sakkinen wrote:
> >> Regarding the recent update of splitting the page permissions change
> >> request into two IOCTLS (RELAX and RESTRICT), can we combine them
> >> into one? That is, revert to how it was done in the v1 version?
> > They are logically separate complex functionalities:
> >
> > 1. "restrict" calls EMODPR and requires EACCEPT 2. "relax" increases
> > permissions up to vetted ("EADD") and could be
> >     combined with EMODPE called inside enclave.
> 
> It would be great to have a _slightly_ better justification than that.
> Existing permission interfaces like chmod or mprotect() don't have this
> asymmetry.
> 
> I think you're saying that the underlying hardware implementation is
> asymmetric, so the interface should be too.  I don't find that argument very
> convincing.  If the hardware interface is arcane and we can make it look more
> sane in the ioctl() layer, we should that, asymmetry or not.
> 

Very nice analogy with `mprotect` and agree to this. It would be simpler from
user space point of view if we can abstract this and maintain a single interface
to relax or restrict permission. But if committee feels having two IOCTLS is the way,
then will modify Gramine to adopt this approach.