linux-kernel - Re: [PATCH V2 03/12] virtio-console: switch to use .validate()

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Date:   Wed, 13 Oct 2021 05:50:56 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, f.hetzelt@...berlin.de,
        david.kaplan@....com, konrad.wilk@...cle.com,
        Amit Shah <amit@...nel.org>
Subject: Re: [PATCH V2 03/12] virtio-console: switch to use .validate()

On Tue, Oct 12, 2021 at 02:52:18PM +0800, Jason Wang wrote:
> This patch switches to use validate() to filter out the features that
> is not supported by the rproc.

are not supported

> 
> Cc: Amit Shah <amit@...nel.org>
> Signed-off-by: Jason Wang <jasowang@...hat.com>


Does this have anything to do with hardening?

It seems cleaner to not negotiate features we do not use,
but given we did this for many years ... should we bother
at this point?


> ---
>  drivers/char/virtio_console.c | 41 ++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 7eaf303a7a86..daeed31df622 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1172,9 +1172,7 @@ static void resize_console(struct port *port)
>  
>  	vdev = port->portdev->vdev;
>  
> -	/* Don't test F_SIZE at all if we're rproc: not a valid feature! */
> -	if (!is_rproc_serial(vdev) &&
> -	    virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
> +	if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
>  		hvc_resize(port->cons.hvc, port->cons.ws);
>  }
>  
> @@ -1981,6 +1979,29 @@ static void virtcons_remove(struct virtio_device *vdev)
>  	kfree(portdev);
>  }
>  
> +static int virtcons_validate(struct virtio_device *vdev)
> +{
> +	if (is_rproc_serial(vdev)) {
> +		/* Don't test F_SIZE at all if we're rproc: not a
> +		 * valid feature! */


This comment needs to be fixed now. And the format's wrong
since you made it a multi-line comment.
Should be
	/*
	 * like
	 * this
	 */

> +		__virtio_clear_bit(vdev, VIRTIO_CONSOLE_F_SIZE);
> +		/* Don't test MULTIPORT at all if we're rproc: not a
> +		 * valid feature! */
> +		__virtio_clear_bit(vdev, VIRTIO_CONSOLE_F_MULTIPORT);
> +	}
> +
> +	/* We only need a config space if features are offered */
> +	if (!vdev->config->get &&
> +	    (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE)
> +	     || virtio_has_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT))) {
> +		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> +			__func__);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Once we're further in boot, we get probed like any other virtio
>   * device.

This switches the order of tests around, so if an rproc device
offers VIRTIO_CONSOLE_F_SIZE or VIRTIO_CONSOLE_F_MULTIPORT
without get it will now try to work instead of failing.

Which is maybe a worthy goal, but given rproc does not support
virtio 1.0 it also risks trying to drive something completely
unreasonable.

Overall does not feel like hardening which is supposed to make
things more strict, not less.


> @@ -1996,15 +2017,6 @@ static int virtcons_probe(struct virtio_device *vdev)
>  	bool multiport;
>  	bool early = early_put_chars != NULL;
>  
> -	/* We only need a config space if features are offered */
> -	if (!vdev->config->get &&
> -	    (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE)
> -	     || virtio_has_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT))) {
> -		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> -			__func__);
> -		return -EINVAL;
> -	}
> -
>  	/* Ensure to read early_put_chars now */
>  	barrier();
>  
> @@ -2031,9 +2043,7 @@ static int virtcons_probe(struct virtio_device *vdev)
>  	multiport = false;
>  	portdev->max_nr_ports = 1;
>  
> -	/* Don't test MULTIPORT at all if we're rproc: not a valid feature! */
> -	if (!is_rproc_serial(vdev) &&
> -	    virtio_cread_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
> +	if (virtio_cread_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
>  				 struct virtio_console_config, max_nr_ports,
>  				 &portdev->max_nr_ports) == 0) {
>  		multiport = true;
> @@ -2210,6 +2220,7 @@ static struct virtio_driver virtio_console = {
>  	.driver.name =	KBUILD_MODNAME,
>  	.driver.owner =	THIS_MODULE,
>  	.id_table =	id_table,
> +	.validate = 	virtcons_validate,
>  	.probe =	virtcons_probe,
>  	.remove =	virtcons_remove,
>  	.config_changed = config_intr,
> -- 
> 2.25.1