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

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Date:   Thu, 30 Sep 2021 06:36:18 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Jason Wang <jasowang@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for
 confidential guest

On Thu, Sep 30, 2021 at 4:03 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Wed, Sep 29, 2021 at 06:05:09PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > 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 <dan.j.williams@...el.com>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.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/
[2]: https://lore.kernel.org/all/YQzF%2FutgrJfbZuHh@kroah.com/

> 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?