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

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Message-ID: <Yav0/3jeJsuT3yEq@iki.fi>
Date:   Sun, 5 Dec 2021 01:08:47 +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 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.

> 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

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

/Jarkko