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

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Date:   Thu, 17 Mar 2022 06:30:29 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     Haitao Huang <haitao.huang@...ux.intel.com>,
        "Dhanraj, Vijay" <vijay.dhanraj@...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, Mar 14, 2022 at 08:32:28AM -0700, Reinette Chatre wrote:
> Hi Jarkko,
> 
> On 3/13/2022 8:42 PM, Jarkko Sakkinen wrote:
> > On Fri, Mar 11, 2022 at 11:28:27AM -0800, Reinette Chatre wrote:
> >> Supporting permission restriction in an ioctl() enables the runtime to manage
> >> the enclave memory without needing to map it.
> > 
> > Which is opposite what you do in EAUG. You can also augment pages without
> > needing the map them. Sure you get that capability, but it is quite useless
> > in practice.
> > 
> >> I have considered the idea of supporting the permission restriction with
> >> mprotect() but as you can see in this response I did not find it to be
> >> practical.
> > 
> > Where is it practical? What is your application? How is it practical to
> > delegate the concurrency management of a split mprotect() to user space?
> > How do we get rid off a useless up-call to the host?
> > 
> 
> The email you responded to contained many obstacles against using mprotect()
> but you chose to ignore them and snipped them all from your response. Could
> you please address the issues instead of dismissing them? 

I did read the whole email but did not see anything that would make a case
for fully exposed EMODPR, or having asymmetrical towards how EAUG works.

I had the same discussion with Haitao about PROT_NONE earlier, and am
fully aware that PROT_READ is required.

BR, Jarkko