SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)

[Haitao Huang]

On Wed, 15 May 2019 16:38:58 -0500, Sean Christopherson  
<sean.j.christopherson at intel.com> wrote:

> 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.

If I read code in file_map_prot_check() correctly, only when you request  
W+X at the same time that EXECMEM would be required for MAP_SHARED, right?
If so, I believe SGX enclaves would never need that.