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

Dave Hansen
2021-09-13T19:25:43Z

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.

Windows has these expectations about booting with fully uninitialized
state. There are also a number of environments where QEMU is sandboxed
or drops permissions in a way that prevent free and open access to
/dev/sgx_vepc.

So good so far?