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Date:   Fri, 17 May 2019 09:05:05 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     "Xing, Cedric" <cedric.xing@intel.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        Paul Moore <paul@paul-moore.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        Eric Paris <eparis@parisplace.org>,
        "selinux@vger.kernel.org" <selinux@vger.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Jethro Beekman <jethro@fortanix.com>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Dr. Greg" <greg@enjellic.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "nhorman@redhat.com" <nhorman@redhat.com>,
        "npmccallum@redhat.com" <npmccallum@redhat.com>,
        "Ayoun, Serge" <serge.ayoun@intel.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
        "Huang, Haitao" <haitao.huang@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Svahn, Kai" <kai.svahn@intel.com>, Borislav Petkov <bp@alien8.de>,
        Josh Triplett <josh@joshtriplett.org>,
        "Huang, Kai" <kai.huang@intel.com>,
        David Rientjes <rientjes@google.com>
Subject: Re: SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)
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On Thu, May 16, 2019 at 05:35:16PM -0700, Andy Lutomirski wrote:
> On Thu, May 16, 2019 at 3:23 PM Xing, Cedric <cedric.xing@intel.com> wrote:
> > And if you are with me on that bigger picture, the next question is: what
> > should be the default behavior of security_sgx_mprot() for
> > existing/non-SGX-aware LSM modules/policies? I'd say a reasonable default
> > is to allow R, RW and RX, but not anything else. It'd suffice to get rid of
> > EXECMEM/EXECMOD requirements on enclave applications. For SGX1, EPCM
> > permissions are immutable so it really doesn't matter what
> > security_sgx_mprot() does. For SGX2 and beyond, there's still time and new
> > SGX-aware LSM modules/policies will probably have emerged by then.
> 
> I hadn't thought about the SGX1 vs SGX2 difference.  If the driver
> initially only wants to support SGX1, then I guess we really could get
> away with constraining the EPC flags based on the source page
> permission and not restricting mprotect() and mmap() permissions on
> /dev/sgx/enclave at all.

No, SGX1 vs SGX2 support in the kernel is irrelevant.  Well, unless the
driver simply refuses to load on SGX2 hardware, but I don't think anyone
wants to go that route.  There is no enabling or attribute bit required
to execute ENCLU[EMODPE], e.g. an enclave can effect RW->RWX in the EPCM
on SGX2 hardware regardless of what the kernel is doing.

IMO the kernel should ignore the EPCM from an LSM perspective.