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

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Date:   Tue, 28 Dec 2021 16:56:29 +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, Dec 13, 2021 at 02:12:44PM -0800, Reinette Chatre wrote:
> 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?

Yeah, let's continue with two ioctls for now, I agree.

/Jarkko