Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

Jarkko Sakkinen
2021-09-13T21:16:42Z

On Mon, 2021-09-13 at 12:25 -0700, Dave Hansen wrote:
> On 9/13/21 11:35 AM, Paolo Bonzini wrote:
> > > > Apart from reclaiming, /dev/sgx_vepc might disappear between the first
> > > > open() and subsequent ones.
> > >
> > > Aside from it being rm'd, I don't think that's possible.
> > >
> >
> > Being rm'd would be a possibility in principle, and it would be ugly for
> > it to cause issues on running VMs. Also I'd like for it to be able to
> > pass /dev/sgx_vepc in via a file descriptor, and run QEMU in a chroot or
> > a mount namespace. Alternatively, with seccomp it may be possible to
> > sandbox a running QEMU process in such a way that open() is forbidden at
> > runtime (all hotplug is done via file descriptor passing); it is not yet
> > possible, but it is a goal.
>
> OK, so maybe another way of saying this:
>
> For bare-metal SGX on real hardware, the hardware provides guarantees
> SGX state at reboot. For instance, all pages start out uninitialized.
> The vepc driver provides a similar guarantee today for freshly-opened
> vepc instances.
>
> But, vepc users have a problem: they might want to run an OS that
> expects to be booted with clean, fully uninitialized SGX state, just as
> it would be on bare-metal. Right now, the only way to get that is to
> create a new vepc instance. That might not be possible in all
> configurations, like if the permission to open(/dev/sgx_vepc) has been
> lost since the VM was first booted.

So you maintain your systems in a way that this does not happen?

/Jarkko