On Mon, Aug 23, 2021 at 7:17 AM Max Gurtovoy [off-list ref] wrote:

On 8/9/2021 1:16 PM, Xie Yongji wrote:

quoted

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@bytedance.com/ (local)

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().

quoted

And we also double check the value in virtblk_probe() in
case that it's changed after the validation.

Signed-off-by: Xie Yongji <redacted>
---
  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