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Date:   Wed, 15 May 2019 14:38:58 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
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Subject: Re: SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)
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On Wed, May 15, 2019 at 11:27:04AM -0700, Andy Lutomirski wrote:
> 2) Just like any other DSO, there are potential issues with how
> enclaves deal with writable vs executable memory.  This takes two
> forms.  First, a task should probably require EXECMEM, EXECMOD, or
> similar permission to run an enclave that can modify its own text.
> Second, it would be nice if a task that did *not* have EXECMEM,
> EXECMOD, or similar could still run the enclave if it had EXECUTE
> permission on the file containing the enclave.
> 
> Currently, this all works because DSOs are run by mmapping the file to
> create multiple VMAs, some of which are executable, non-writable, and
> non-CoWed, and some of which are writable but not executable.  With
> SGX, there's only really one inode per enclave (the anon_inode that
> comes form /dev/sgx/enclave), and it can only be sensibly mapped
> MAP_SHARED.

I was wrong when I said /dev/sgx/enclave creates and returns an anon
inode.  I was thinking of the KVM model for creating VMs.  SGX creates
an enclave when /dev/sgx/enclave is opened and associates the enclave
with the newly opened /dev/sgx/enclave fd.

Regardless, the fundamental problem remains, mmap() of EPC works on a
single inode.