Re: [PATCH v2 3/4] rpmb: create virtio rpmb frontend driver

Harald Mommer
2022-06-16T15:44:21Z

On 05.04.22 11:37, Alex Bennée wrote:
> +++ b/drivers/rpmb/virtio_rpmb.c
> ...
> +static int rpmb_virtio_write_blocks(struct device *dev, u8 target,
> + int len, u8 *req, int rlen, u8 *resp)
> +{
> + struct virtio_rpmb_info *vi = dev_get_drvdata(dev);
> + struct virtio_rpmb_frame *request = (struct virtio_rpmb_frame *) req;
> + struct virtio_rpmb_frame *response = (struct virtio_rpmb_frame *) resp;
> + struct scatterlist out_frame;
> + struct scatterlist in_frame;
> + struct scatterlist *sgs[2];
> + int blocks, data_len, received;
> +
> + if (!len || (len % VIRTIO_RPMB_FRAME_SZ) != 0 || !request)
> + return -EINVAL;
> +
> + /* The first frame will contain the details of the request */
> + if (be16_to_cpu(request->req_resp) != VIRTIO_RPMB_REQ_DATA_WRITE)
> + return -EINVAL;
> +
> + blocks = be16_to_cpu(request->block_count);
> + if (blocks > vi->max_wr)
> + return -EINVAL;

Not exactly. The virtio specification reserves 0 for "unlimited". And I
see no special handling for 0 in your code. Damned trap in the
specification.

What's "unlimited"? As the blocks_count in the rpmb frame is a be16 I
guess it's 65535. But if you consider this theoretically you have a
possible max array allocation of 16 MB - 512B max. instead of the 16 KB
- 512B you have with 255. Getting headache about this "unlimited" in the
virtio specification. I don't like the theoretical possibility having to
allocate 16MB dynamically for a moment due to this "unlimited".

And of course there is the same problem in virtio_rpmb_read_blocks()
with max_rd.

A fix is needed, either 0 is 65535 or 0 is 255. Choosing 255 as
implementation decision would be limiting down but maybe without any
practical impact. For UFS it's a single byte bRPMBReadWriteSize only in
JESD220C-2.2 GEOMETRY DESCRIPTOR and 0 is not defined there as
"unlimited". Unfortunately I've no idea about the other possible
underlying technologies (eMMC, NVMe, ...).

> ...
> +}
> +...
> +static int rpmb_virtio_read_blocks(struct device *dev, u8 target,
> + int addr, int count, int len, u8 *data)
> +{
> ...
> + if (count > vi->max_rd)
> + return -EINVAL;
See above.
> ...

--
Dipl.-Ing. Harald Mommer
Senior Software Engineer

OpenSynergy GmbH
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