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

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Message-ID: <f6a256a6-a7d7-a8e7-c9a8-e232203c63af@intel.com>
Date:   Mon, 28 Feb 2022 07:16:22 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        "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 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.

If we can't make it any more sane, let's say why the ioctl() must or
should be asymmetric.

The SGX2 page permission mechanism is horribly counter intuitive.
*Everybody* that looks at it thinks that it's wrong.  That means that we
have a lot of work ahead of us to explain the interfaces that get
layered on top.