RE: [PATCH v1 00/15] Add support for Nitro Enclaves

Tian, Kevin
2020-04-26T08:16:44Z

> From: Paraschiv, Andra-Irina <andraprs@amazon.com>
> Sent: Friday, April 24, 2020 9:59 PM
>
>
> On 24/04/2020 12:59, Tian, Kevin wrote:
> >
> >> From: Paraschiv, Andra-Irina
> >> Sent: Thursday, April 23, 2020 9:20 PM
> >>
> >> On 22/04/2020 00:46, Paolo Bonzini wrote:
> >>> On 21/04/20 20:41, Andra Paraschiv wrote:
> >>>> An enclave communicates with the primary VM via a local
> communication
> >> channel,
> >>>> using virtio-vsock [2]. An enclave does not have a disk or a network
> device
> >>>> attached.
> >>> Is it possible to have a sample of this in the samples/ directory?
> >> I can add in v2 a sample file including the basic flow of how to use the
> >> ioctl interface to create / terminate an enclave.
> >>
> >> Then we can update / build on top it based on the ongoing discussions on
> >> the patch series and the received feedback.
> >>
> >>> I am interested especially in:
> >>>
> >>> - the initial CPU state: CPL0 vs. CPL3, initial program counter, etc.
> >>>
> >>> - the communication channel; does the enclave see the usual local APIC
> >>> and IOAPIC interfaces in order to get interrupts from virtio-vsock, and
> >>> where is the virtio-vsock device (virtio-mmio I suppose) placed in
> memory?
> >>>
> >>> - what the enclave is allowed to do: can it change privilege levels,
> >>> what happens if the enclave performs an access to nonexistent memory,
> >> etc.
> >>> - whether there are special hypercall interfaces for the enclave
> >> An enclave is a VM, running on the same host as the primary VM, that
> >> launched the enclave. They are siblings.
> >>
> >> Here we need to think of two components:
> >>
> >> 1. An enclave abstraction process - a process running in the primary VM
> >> guest, that uses the provided ioctl interface of the Nitro Enclaves
> >> kernel driver to spawn an enclave VM (that's 2 below).
> >>
> >> How does all gets to an enclave VM running on the host?
> >>
> >> There is a Nitro Enclaves emulated PCI device exposed to the primary VM.
> >> The driver for this new PCI device is included in the current patch series.
> >>
> >> The ioctl logic is mapped to PCI device commands e.g. the
> >> NE_ENCLAVE_START ioctl maps to an enclave start PCI command or the
> >> KVM_SET_USER_MEMORY_REGION maps to an add memory PCI
> command.
> >> The PCI
> >> device commands are then translated into actions taken on the hypervisor
> >> side; that's the Nitro hypervisor running on the host where the primary
> >> VM is running.
> >>
> >> 2. The enclave itself - a VM running on the same host as the primary VM
> >> that spawned it.
> >>
> >> The enclave VM has no persistent storage or network interface attached,
> >> it uses its own memory and CPUs + its virtio-vsock emulated device for
> >> communication with the primary VM.
> > sounds like a firecracker VM?
>
> It's a VM crafted for enclave needs.
>
> >
> >> The memory and CPUs are carved out of the primary VM, they are
> dedicated
> >> for the enclave. The Nitro hypervisor running on the host ensures memory
> >> and CPU isolation between the primary VM and the enclave VM.
> > In last paragraph, you said that the enclave VM uses its own memory and
> > CPUs. Then here, you said the memory/CPUs are carved out and dedicated
> > from the primary VM. Can you elaborate which one is accurate? or a mixed
> > model?
>
> Memory and CPUs are carved out of the primary VM and are dedicated for
> the enclave VM. I mentioned above as "its own" in the sense that the
> primary VM doesn't use these carved out resources while the enclave is
> running, as they are dedicated to the enclave.
>
> Hope that now it's more clear.

yes, it's clearer.

>
> >
> >>
> >> These two components need to reflect the same state e.g. when the
> >> enclave abstraction process (1) is terminated, the enclave VM (2) is
> >> terminated as well.
> >>
> >> With regard to the communication channel, the primary VM has its own
> >> emulated virtio-vsock PCI device. The enclave VM has its own emulated
> >> virtio-vsock device as well. This channel is used, for example, to fetch
> >> data in the enclave and then process it. An application that sets up the
> >> vsock socket and connects or listens, depending on the use case, is then
> >> developed to use this channel; this happens on both ends - primary VM
> >> and enclave VM.
> > How does the application in the primary VM assign task to be executed
> > in the enclave VM? I didn't see such command in this series, so suppose
> > it is also communicated through virtio-vsock?
>
> The application that runs in the enclave needs to be packaged in an
> enclave image together with the OS ( e.g. kernel, ramdisk, init ) that
> will run in the enclave VM.
>
> Then the enclave image is loaded in memory. After booting is finished,
> the application starts. Now, depending on the app implementation and use
> case, one example can be that the app in the enclave waits for data to
> be fetched in via the vsock channel.
>

OK, I thought the code/data was dynamically injected from the primary
VM and then run in the enclave. From your description it sounds like
a servicing model that an auto-running application wait for and respond
service request from the application in the primary VM.

Thanks
Kevin