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

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Date:   Sat, 11 Dec 2021 09:57:51 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
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

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.

> 
> > 
> > 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).

> Reinette

/Jarkko