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

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Message-ID: <20210930065953-mutt-send-email-mst@kernel.org>
Date:   Thu, 30 Sep 2021 07:03:36 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Borislav Petkov <bp@...en8.de>, 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>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-usb@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for
 confidential guest

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.
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.

> ---
>  drivers/virtio/virtio.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 588e02fb91d3..377b0ccdc503 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -5,6 +5,8 @@
>  #include <linux/module.h>
>  #include <linux/idr.h>
>  #include <linux/of.h>
> +#include <linux/cc_platform.h>
> +#include <linux/device.h>
>  #include <uapi/linux/virtio_ids.h>
>  
>  /* Unique numbering for virtio devices. */
> @@ -390,6 +392,13 @@ int register_virtio_device(struct virtio_device *dev)
>  	dev->config_enabled = false;
>  	dev->config_change_pending = false;
>  
> +	/*
> +	 * For Confidential guest (like TDX), virtio devices are
> +	 * trusted. So set authorized status as true.
> +	 */
> +	if (cc_platform_has(CC_ATTR_GUEST_DEVICE_FILTER))
> +		dev->dev.authorized = true;
> +
>  	/* We always start by resetting the device, in case a previous
>  	 * driver messed it up.  This also tests that code path a little. */
>  	dev->config->reset(dev);
> -- 
> 2.25.1