Re: x86/sgx: uapi change proposal

[Jarkko Sakkinen]

On Fri, Dec 21, 2018 at 10:24:54AM -0800, Sean Christopherson wrote:
> On Fri, Dec 21, 2018 at 09:12:46AM -0800, Andy Lutomirski wrote:
> > > 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 :)
> 
> Mmmm, I like this approach a lot.  It would allow userspace to easily
> manage permissions for each "feature", e.g. give all users access to
> /dev/sgx/epc but restrict /dev/sgx/enclave.
> 
> And we could add e.g. /dev/sgx/admin if we wanted to exposed ioctls()
> that apply to all aspects of SGX.
> 
> Do you know if /dev/sgx/epc could be dynamically created, e.g. by
> KVM when the kvm_intel module is loaded?  That would seal the deal for
> me as it'd keep open the option of having KVM handle oversubscription
> of guest EPC while exposing EPC through /dev/sgx instead of /dev/kvm.  

No issues with this approach from my side but won't use it for v19.

Please share these comments when reviewing v19. Neither objections to
have this interface.

/Jarkko