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

[Reinette Chatre]

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