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Subject: Re: [PATCH v5] virtio-blk: Add validation for block size in config
 space
To:     Xie Yongji <xieyongji@bytedance.com>, <mst@redhat.com>,
        <jasowang@redhat.com>, <stefanha@redhat.com>
CC:     <virtualization@lists.linux-foundation.org>,
        <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20210809101609.148-1-xieyongji@bytedance.com>
From:   Max Gurtovoy <mgurtovoy@nvidia.com>
Message-ID: <e6ab104e-a18b-3f17-9cd8-6a6b689b56b4@nvidia.com>
Date:   Mon, 23 Aug 2021 02:17:21 +0300
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On 8/9/2021 1:16 PM, Xie Yongji wrote:
> An untrusted device might presents an invalid block size
> in configuration space. This tries to add validation for it
> in the validate callback and clear the VIRTIO_BLK_F_BLK_SIZE
> feature bit if the value is out of the supported range.

This is not clear to me. What is untrusted device ? is it a buggy device ?

What is the return value for the blk_size in this case that you try to 
override ?


>
> And we also double check the value in virtblk_probe() in
> case that it's changed after the validation.
>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> ---
>   drivers/block/virtio_blk.c | 39 +++++++++++++++++++++++++++++++++------
>   1 file changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 4b49df2dfd23..afb37aac09e8 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -692,6 +692,28 @@ static const struct blk_mq_ops virtio_mq_ops = {
>   static unsigned int virtblk_queue_depth;
>   module_param_named(queue_depth, virtblk_queue_depth, uint, 0444);
>   
> +static int virtblk_validate(struct virtio_device *vdev)
> +{
> +	u32 blk_size;
> +
> +	if (!vdev->config->get) {
> +		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> +			__func__);
> +		return -EINVAL;
> +	}
> +
> +	if (!virtio_has_feature(vdev, VIRTIO_BLK_F_BLK_SIZE))
> +		return 0;
> +
> +	blk_size = virtio_cread32(vdev,
> +			offsetof(struct virtio_blk_config, blk_size));
> +
> +	if (blk_size < SECTOR_SIZE || blk_size > PAGE_SIZE)
> +		__virtio_clear_bit(vdev, VIRTIO_BLK_F_BLK_SIZE);

is it PAGE_SIZE or SZ_4K ?

Do we support a 64K blk size (PPC PAGE_SIZE)

> +
> +	return 0;
> +}
> +
>   static int virtblk_probe(struct virtio_device *vdev)
>   {
>   	struct virtio_blk *vblk;
> @@ -703,12 +725,6 @@ static int virtblk_probe(struct virtio_device *vdev)
>   	u8 physical_block_exp, alignment_offset;
>   	unsigned int queue_depth;
>   
> -	if (!vdev->config->get) {
> -		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> -			__func__);
> -		return -EINVAL;
> -	}
> -
>   	err = ida_simple_get(&vd_index_ida, 0, minor_to_index(1 << MINORBITS),
>   			     GFP_KERNEL);
>   	if (err < 0)
> @@ -823,6 +839,14 @@ static int virtblk_probe(struct virtio_device *vdev)
>   	else
>   		blk_size = queue_logical_block_size(q);
>   
> +	if (unlikely(blk_size < SECTOR_SIZE || blk_size > PAGE_SIZE)) {
> +		dev_err(&vdev->dev,
> +			"block size is changed unexpectedly, now is %u\n",
> +			blk_size);
> +		err = -EINVAL;
> +		goto err_cleanup_disk;
> +	}
> +
>   	/* Use topology information if available */
>   	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
>   				   struct virtio_blk_config, physical_block_exp,
> @@ -881,6 +905,8 @@ static int virtblk_probe(struct virtio_device *vdev)
>   	device_add_disk(&vdev->dev, vblk->disk, virtblk_attr_groups);
>   	return 0;
>   
> +err_cleanup_disk:
> +	blk_cleanup_disk(vblk->disk);
>   out_free_tags:
>   	blk_mq_free_tag_set(&vblk->tag_set);
>   out_free_vq:
> @@ -983,6 +1009,7 @@ static struct virtio_driver virtio_blk = {
>   	.driver.name			= KBUILD_MODNAME,
>   	.driver.owner			= THIS_MODULE,
>   	.id_table			= id_table,
> +	.validate			= virtblk_validate,
>   	.probe				= virtblk_probe,
>   	.remove				= virtblk_remove,
>   	.config_changed			= virtblk_config_changed,