linux-kernel - Re: [PATCH V3] virtio: disable notification hardening by default

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Date:   Wed, 22 Jun 2022 10:32:26 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jason Wang <jasowang@...hat.com>, pasic@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, borntraeger@...ibm.com,
        agordeev@...ux.ibm.com, mst@...hat.com, jasowang@...hat.com,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     ben@...adent.org.uk, david@...hat.com
Subject: Re: [PATCH V3] virtio: disable notification hardening by default

On Wed, Jun 22 2022, Jason Wang <jasowang@...hat.com> wrote:

> We try to harden virtio device notifications in 8b4ec69d7e09 ("virtio:
> harden vring IRQ"). It works with the assumption that the driver or
> core can properly call virtio_device_ready() at the right
> place. Unfortunately, this seems to be not true and uncover various
> bugs of the existing drivers, mainly the issue of using
> virtio_device_ready() incorrectly.
>
> So let's having a Kconfig option and disable it by default. It gives

s/having/have/

> us a breath to fix the drivers and then we can consider to enable it
> by default.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> Changes since V2:
> - Tweak the Kconfig help
> - Add comment for the read_lock() pairing in virtio_ccw
> ---
>  drivers/s390/virtio/virtio_ccw.c |  9 ++++++++-
>  drivers/virtio/Kconfig           | 13 +++++++++++++
>  drivers/virtio/virtio.c          |  2 ++
>  drivers/virtio/virtio_ring.c     | 12 ++++++++++++
>  include/linux/virtio_config.h    |  2 ++
>  5 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index 97e51c34e6cf..1f6a358f65f0 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -1136,8 +1136,13 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
>  			vcdev->err = -EIO;
>  	}
>  	virtio_ccw_check_activity(vcdev, activity);
> -	/* Interrupts are disabled here */
> +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> +	/*
> +	 * Paried with virtio_ccw_synchronize_cbs() and interrupts are

s/Paried/Paired/

> +	 * disabled here.
> +	 */
>  	read_lock(&vcdev->irq_lock);
> +#endif
>  	for_each_set_bit(i, indicators(vcdev),
>  			 sizeof(*indicators(vcdev)) * BITS_PER_BYTE) {
>  		/* The bit clear must happen before the vring kick. */
> @@ -1146,7 +1151,9 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
>  		vq = virtio_ccw_vq_by_ind(vcdev, i);
>  		vring_interrupt(0, vq);
>  	}
> +#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
>  	read_unlock(&vcdev->irq_lock);
> +#endif
>  	if (test_bit(0, indicators2(vcdev))) {
>  		virtio_config_changed(&vcdev->vdev);
>  		clear_bit(0, indicators2(vcdev));


Reviewed-by: Cornelia Huck <cohuck@...hat.com>