linux-kernel - Re: [PATCH 10/25] x86/sgx: Support enclave page permission changes

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Date:   Mon, 6 Dec 2021 13:42:08 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
CC:     <dave.hansen@...ux.intel.com>, <tglx@...utronix.de>,
        <bp@...en8.de>, <luto@...nel.org>, <mingo@...hat.com>,
        <linux-sgx@...r.kernel.org>, <x86@...nel.org>, <seanjc@...gle.com>,
        <kai.huang@...el.com>, <cathy.zhang@...el.com>,
        <cedric.xing@...el.com>, <haitao.huang@...el.com>,
        <mark.shanahan@...el.com>, <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/25] x86/sgx: Support enclave page permission changes

Hi Jarkko,

On 12/4/2021 3:08 PM, Jarkko Sakkinen wrote:
> On Wed, Dec 01, 2021 at 11:23:08AM -0800, Reinette Chatre wrote:
>> In the initial (SGX1) version of SGX, pages in an enclave need to be
>> created with permissions that support all usages of the pages, from the
>> time the enclave is initialized until it is unloaded. For example,
>> pages used by a JIT compiler or when code needs to otherwise be
>> relocated need to always have RWX permissions.
>>
>> SGX2 includes two functions that can be used to modify the enclave page
>> permissions of regular enclave pages within an initialized enclave.
>> ENCLS[EMODPR] is run from the OS and used to restrict enclave page
>> permissions while ENCLU[EMODPE] is run from within the enclave to
>> extend enclave page permissions.
>>
>> Enclave page permission changes need to be approached with care and
>> for this reason this initial support is to allow enclave page
>> permission changes _only_ if the new permissions are the same or
>> more restrictive that the permissions originally vetted at the time the
>> pages were added to the enclave. Support for extending enclave page
>> permissions beyond what was originally vetted is deferred.
> 
> This paragraph is out-of-scope for a commit message. You could have
> this in the cover letter but not here. I would just remove it.

I think this is essential information that is mentioned in the cover 
letter _and_ in this changelog. I will follow Dave's guidance and avoid 
"deferred" by just removing that last sentence.

> 
>> Whether enclave page permissions are restricted or extended it
>> is necessary to ensure that the page table entries and enclave page
>> permissions are in sync. Introduce a new ioctl, SGX_IOC_PAGE_MODP, to
> 
> SGX_IOC_PAGE_MODP does not match the naming convetion of these:
> 
> * SGX_IOC_ENCLAVE_CREATE
> * SGX_IOC_ENCLAVE_ADD_PAGES
> * SGX_IOC_ENCLAVE_INIT

ah - my understanding was that the SGX_IOC_ENCLAVE prefix related to 
operations related to the entire enclave and thus I introduced the 
prefix SGX_IOC_PAGE to relate to operations on pages within an enclave.

> 
> A better name would be SGX_IOC_ENCLAVE_MOD_PROTECTIONS. It doesn't
> do harm to be a more verbose.

Will do. I see later you propose SGX_IOC_ENCLAVE_MODIFY_TYPE - would you 
like them to be consistent wrt MOD/MODIFY?

Reinette