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

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Date:   Mon, 13 Dec 2021 14:12:44 -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 12/10/2021 11:57 PM, Jarkko Sakkinen wrote:
> On Mon, 2021-12-06 at 13:42 -0800, Reinette Chatre wrote:
>> 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.
> 
> SGX_IOC_ENCLAVE_ADD_PAGES is also operation working on pages within an
> enclave.
> 
> Also, to be aligned with SGX_IOC_ENCLAVE_ADD_PAGES, the new operations
> should also take secinfo as input.

ok, will do.

> 
>>
>>>
>>> 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?
> 
> I would considering introducing just one new ioctl:
> 
>    SGX_IOC_ENCLAVE_MODIFY_PAGES
> 
> and choose either operations based on e.g. a flag
> (see flags field SGX_IOC_ENCLAVE_ADD_PAGES).
> 

There seems to be different opinion about the single ioctl() as 
per:https://lore.kernel.org/lkml/0fb14185-5cc3-a963-253d-2e119b4a52bb@intel.com/

I thus plan to proceed with the two ioctls, both taking secinfo as 
input. Would that be ok with you?

Reinette