Re: x86/sgx: uapi change proposal

[Andy Lutomirski]

> On Dec 21, 2018, at 9:28 AM, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote:
>
> On Wed, Dec 19, 2018 at 06:58:48PM -0800, Andy Lutomirski wrote:
>>> On Dec 19, 2018, at 6:45 AM, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote:
>>>
>>>>> On Wed, Dec 19, 2018 at 09:36:16AM +0000, Jethro Beekman wrote:
>>>
>>> I agree with Jethro, passing the enclave_fd as a param is obnoxious.
>>> And it means the user needs to open /dev/sgx to do anything with an
>>> enclave fd, e.g. the enclave fd might be passed to a builder thread,
>>> it shouldn't also need the device fd.
>>>
>>> E.g.:
>>>
>>>   sgx_fd = open("/dev/sgx", O_RDWR);
>>>   BUG_ON(sgx_fd < 0);
>>>
>>>   enclave_fd = ioctl(sgx_fd, SGX_ENCLAVE_CREATE, &ecreate);
>>>   BUG_ON(enclave_fd < 0);
>>>
>>>   ret = ioctl(enclave_fd, SGX_ENCLAVE_ADD_PAGE, &eadd);
>>>   BUG_ON(ret);
>>>
>>>   ...
>>>
>>>   ret = ioctl(enclave_fd, SGX_ENCLAVE_INIT, &einit);
>>>   BUG_ON(ret);
>>>
>>>   ...
>>>
>>>   close(enclave_fd);
>>>   close(sgx_fd);
>>>
>>>
>>> Take a look at virt/kvm/kvm_main.c to see how KVM manages anon inodes
>>> and ioctls for VMs and vCPUs.
>>
>> Can one of you explain why SGX_ENCLAVE_CREATE is better than just
>> opening a new instance of /dev/sgx for each encalve?
>
> Directly associating /dev/sgx with an enclave means /dev/sgx can't be
> used to provide ioctl()'s for other SGX-related needs, e.g. to mmap()
> raw EPC and expose it a VM.  Proposed layout in the link below.  I'll
> also respond to Jarkko's question about exposing EPC through /dev/sgx
> instead of having KVM allocate it on behalf of the VM.

Hmm. I guess this makes some sense.  My instinct would be to do it a
little differently and have:

/dev/sgx/enclave: Each instance is an enclave.

/dev/sgx/epc: Used to get raw EPC for KVM. Might have different
permissions, perhaps 0660 and group kvm.

/dev/sgx/something_else: For when SGX v3 adds something else :)