Re: [PATCH v2 0/4] Add blk_validate_block_size() helper for drivers to validate block size

Re: [PATCH v2 0/4] Add blk_validate_block_size() helper for drivers to validate block size

[Michael S. Tsirkin]

On Mon, Oct 25, 2021 at 10:25:02PM +0800, Xie Yongji wrote:
> The block layer can't support the block size larger than
> page size yet, so driver needs to validate the block size
> before setting it. Now this validation is done in device drivers
> with some duplicated codes. This series tries to add a block
> layer helper for it and makes loop driver, nbd driver and
> virtio-blk driver use it.
> 
> V1 to V2:
> - Return and print error if validation fails in virtio-blk driver

Please document how all this was tested.

> Xie Yongji (4):
>   block: Add a helper to validate the block size
>   nbd: Use blk_validate_block_size() to validate block size
>   loop: Use blk_validate_block_size() to validate block size
>   virtio-blk: Use blk_validate_block_size() to validate block size
> 
>  drivers/block/loop.c       | 17 ++---------------
>  drivers/block/nbd.c        |  3 ++-
>  drivers/block/virtio_blk.c | 11 +++++++++--
>  include/linux/blkdev.h     |  8 ++++++++
>  4 files changed, 21 insertions(+), 18 deletions(-)
> 
> -- 
> 2.11.0

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Re: [PATCH v2 4/4] virtio-blk: Use blk_validate_block_size() to validate block size

[Michael S. Tsirkin]

On Mon, Oct 25, 2021 at 10:25:06PM +0800, Xie Yongji wrote:
> The block layer can't support the block size larger than

the block size -> block sizes, or a block size

> page size yet.

And to add to that, a block size that's too small or
not a power of two won't work either, right?
Mention that too.


> If an untrusted device

nothing to do with trust. A misconfigured device.

> presents an invalid
> block size in configuration space, it will result in the
> kernel crash something like below:
> 
> [  506.154324] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [  506.160416] RIP: 0010:create_empty_buffers+0x24/0x100
> [  506.174302] Call Trace:
> [  506.174651]  create_page_buffers+0x4d/0x60
> [  506.175207]  block_read_full_page+0x50/0x380
> [  506.175798]  ? __mod_lruvec_page_state+0x60/0xa0
> [  506.176412]  ? __add_to_page_cache_locked+0x1b2/0x390
> [  506.177085]  ? blkdev_direct_IO+0x4a0/0x4a0
> [  506.177644]  ? scan_shadow_nodes+0x30/0x30
> [  506.178206]  ? lru_cache_add+0x42/0x60
> [  506.178716]  do_read_cache_page+0x695/0x740
> [  506.179278]  ? read_part_sector+0xe0/0xe0
> [  506.179821]  read_part_sector+0x36/0xe0
> [  506.180337]  adfspart_check_ICS+0x32/0x320
> [  506.180890]  ? snprintf+0x45/0x70
> [  506.181350]  ? read_part_sector+0xe0/0xe0
> [  506.181906]  bdev_disk_changed+0x229/0x5c0
> [  506.182483]  blkdev_get_whole+0x6d/0x90
> [  506.183013]  blkdev_get_by_dev+0x122/0x2d0
> [  506.183562]  device_add_disk+0x39e/0x3c0
> [  506.184472]  virtblk_probe+0x3f8/0x79b [virtio_blk]
> [  506.185461]  virtio_dev_probe+0x15e/0x1d0 [virtio]
> 
> So this patch tries to use the block layer helper to
> validate the block size.

I know you are trying to be polite but it's misplaced here.
Just say what it is:

Use a block layer helper to validate the block size.

> 
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> ---
>  drivers/block/virtio_blk.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 303caf2d17d0..8b5833997f8e 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -815,9 +815,16 @@ static int virtblk_probe(struct virtio_device *vdev)
>  	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
>  				   struct virtio_blk_config, blk_size,
>  				   &blk_size);
> -	if (!err)
> +	if (!err) {
> +		err = blk_validate_block_size(blk_size);
> +		if (err) {
> +			dev_err(&vdev->dev,
> +				"get invalid block size: %u\n", blk_size);

Probably hex. Add virtio_blk: and drop "get" here - it's ungrammatical.
	"virtio_blk: invalid block size: 0x%x\n", blk_size.

> +			goto out_cleanup_disk;
> +		}
> +
>  		blk_queue_logical_block_size(q, blk_size);
> -	else
> +	} else
>  		blk_size = queue_logical_block_size(q);
>  
>  	/* Use topology information if available */
> -- 
> 2.11.0

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