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

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Date:   Mon, 28 Feb 2022 14:19:17 +0100
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     "Dhanraj, Vijay" <vijay.dhanraj@...el.com>
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 Mon, Feb 28, 2022 at 01:25:07PM +0100, Jarkko Sakkinen wrote:
> On Wed, Feb 23, 2022 at 07:21:50PM +0000, Dhanraj, Vijay wrote:
> > Hi All,
> > 
> > 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.
> 
> I don't think it is a good idea.

I.e. in microarchitecture there is no EMODP but two different flows, 
and thus it is not sane to act like there was with that kind of ioctl.
It is as granular as the hardware is this way, and I think that is
common sense.

It would make much sense as combining ECREATE/EADD/EINIT into a single
multi-function ioctl. Often user space needs to be anyway have at least
some logically distinct flows fore these.

BR, Jarkko