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

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>, Andi Kleen <ak@linux.intel.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Michael Jamet <michael.jamet@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	x86@kernel.org, virtualization@lists.linux-foundation.org,
	Yehezkel Bernat <YehezkelShB@gmail.com>,
	Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
	linux-kernel@vger.kernel.org,
	Andreas Noever <andreas.noever@gmail.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-usb@vger.kernel.org,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest
Date: Thu, 30 Sep 2021 07:03:36 -0400	[thread overview]
Message-ID: <20210930065953-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20210930010511.3387967-5-sathyanarayanan.kuppuswamy@linux.intel.com>

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@intel.com>
> 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.
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

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