Re: [PATCH v5] virtio-blk: Add validation for block size in config space

[Yongji Xie <xieyongji@xxxxxxxxxxxxx>]

On Mon, Aug 23, 2021 at 7:17 AM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote:
>
>
> 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 ?
>

A buggy device, the devices in an encrypted VM, or a userspace device
created by VDUSE [1].

[1] https://lore.kernel.org/kvm/20210818120642.165-1-xieyongji@xxxxxxxxxxxxx/

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

The value that is larger than PAGE_SIZE.  I think the block layer can
not handle the block size that is larger than PAGE_SIZE correctly,
e.g. in block_read_full_page().

>
> >
> > 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@xxxxxxxxxxxxx>
> > ---
> >   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)
>

I think PAGE_SIZE should be OK here. I didn't see a hard 4K limitation
in the kernel. NBD did the same check:

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
{
    if (!blksize)
    blksize = NBD_DEF_BLKSIZE;
    if (blksize < 512 || blksize > PAGE_SIZE || !is_power_of_2(blksize))
    return -EINVAL;

Thanks,
Yongji