Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest

On Thu, Sep 30, 2021 at 4:03 AM Michael S. Tsirkin [off-list ref] wrote:

On Wed, Sep 29, 2021 at 06:05:09PM -0700, Kuppuswamy Sathyanarayanan wrote:

quoted

Confidential guest platforms like TDX have a requirement to allow
only trusted devices. By default the confidential-guest core will
arrange for all devices to default to unauthorized (via
dev_default_authorization) in device_initialize(). Since virtio
driver is already hardened against the attack from the un-trusted host,
override the confidential computing default unauthorized state

Reviewed-by: Dan Williams <redacted>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Architecturally this all looks backwards. IIUC nothing about virtio
makes it authorized or trusted. The driver is hardened,
true, but this should be set at the driver not the device level.

That's was my initial reaction to this proposal as well, and I ended
up leading Sathya astray from what Greg wanted. Greg rightly points
out that the "authorized" attribute from USB and Thunderbolt already
exists [1] [2]. So the choice is find an awkward way to mix driver
trust with existing bus-local "authorized" mechanisms, or promote the
authorized capability to the driver-core. This patch set implements
the latter to keep the momentum on the already shipping design scheme
to not add to the driver-core maintenance burden.

[1]: https://lore.kernel.org/all/YQuaJ78y8j1UmBoz@kroah.com/ (local)
[2]: https://lore.kernel.org/all/YQzF%2FutgrJfbZuHh@kroah.com/ (local)

And in particular, not all virtio drivers are hardened -
I think at this point blk and scsi drivers have been hardened - so
treating them all the same looks wrong.

My understanding was that they have been audited, Sathya?
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