linux-kernel - Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove

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Message-ID: <fa8e8573-d907-11b0-60e1-f31e050beb64@intel.com>
Date:   Mon, 13 Sep 2021 12:25:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org, jarkko@...nel.org,
        dave.hansen@...ux.intel.com, yang.zhong@...el.com
Subject: Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

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?