RE: [PATCH v4 1/3] rpmb: add Replay Protected Memory Block (RPMB) subsystem

[Avri Altman]

> A number of storage technologies support a specialised hardware
> partition designed to be resistant to replay attacks. The underlying
> HW protocols differ but the operations are common. The RPMB partition
> cannot be accessed via standard block layer, but by a set of specific
> RPMB commands: WRITE, READ, GET_WRITE_COUNTER, and PROGRAM_KEY.
What about the other rpmb operations?
There are 7 operations in eMMC.

............

> +/**
> + * rpmb_dev_find_device() - return first matching rpmb device
> + * @data: data for the match function
> + * @match: the matching function
> + *
> + * Iterate over registered RPMB devices, and call @match() for each passing
> + * it the RPMB device and @data.
> + *
> + * The return value of @match() is checked for each call. If it returns
> + * anything other 0, break and return the found RPMB device.
> + *
> + * It's the callers responsibility to call rpmb_dev_put() on the returned
> + * device, when it's done with it.
> + *
> + * Returns: a matching rpmb device or NULL on failure
> + */
> +struct rpmb_dev *rpmb_dev_find_device(const void *data,
> +                                     const struct rpmb_dev *start,
> +                                     int (*match)(struct rpmb_dev *rdev,
> +                                                  const void *data))
> +{
> +       struct rpmb_dev *rdev;
> +       struct list_head *pos;
> +
> +       mutex_lock(&rpmb_mutex);
> +       if (start)
> +               pos = start->list_node.next;
> +       else
> +               pos = rpmb_dev_list.next;
> +
> +       while (pos != &rpmb_dev_list) {
Why not just list_for_each_entry instead?

> +               rdev = container_of(pos, struct rpmb_dev, list_node);
> +               if (match(rdev, data)) {
> +                       rpmb_dev_get(rdev);
> +                       goto out;
> +               }
> +               pos = pos->next;
> +       }
> +       rdev = NULL;
> +
> +out:
> +       mutex_unlock(&rpmb_mutex);
> +
> +       return rdev;
> +}

.....................

> +/**
> + * rpmb_dev_register - register RPMB partition with the RPMB subsystem
> + * @dev: storage device of the rpmb device
> + * @ops: device specific operations
> + *
> + * While registering the RPMB partition extract needed device information
> + * while needed resources are available.
> + *
> + * Returns: a pointer to a 'struct rpmb_dev' or an ERR_PTR on failure
> + */
> +struct rpmb_dev *rpmb_dev_register(struct device *dev,
> +                                  struct rpmb_descr *descr)
> +{
> +       struct rpmb_dev *rdev;
> +
> +       if (!dev || !descr || !descr->route_frames || !descr->dev_id ||
> +           !descr->dev_id_len)
> +               return ERR_PTR(-EINVAL);
> +
> +       rdev = kzalloc(sizeof(*rdev), GFP_KERNEL);
> +       if (!rdev)
> +               return ERR_PTR(-ENOMEM);
> +       rdev->descr = *descr;
> +       rdev->descr.dev_id = kmemdup(descr->dev_id, descr->dev_id_len,
> +                                    GFP_KERNEL);
In addition to the dev_id, wouldn't it make sense to have your own IDA as well?

> +       if (!rdev->descr.dev_id) {
> +               kfree(rdev);
> +               return ERR_PTR(-ENOMEM);
> +       }
> +
> +       rdev->parent_dev = dev;
> +
> +       dev_dbg(rdev->parent_dev, "registered device\n");
> +
> +       mutex_lock(&rpmb_mutex);
> +       list_add_tail(&rdev->list_node, &rpmb_dev_list);
> +       blocking_notifier_call_chain(&rpmb_interface,
> RPMB_NOTIFY_ADD_DEVICE,
> +                                    rdev);
> +       mutex_unlock(&rpmb_mutex);
> +
> +       return rdev;
> +}
> +EXPORT_SYMBOL_GPL(rpmb_dev_register);

............

> new file mode 100644
> index 000000000000..251d6b7e6d15
> --- /dev/null
> +++ b/include/linux/rpmb.h
> @@ -0,0 +1,136 @@
> +/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0 */
> +/*
> + * Copyright (C) 2015-2019 Intel Corp. All rights reserved
> + * Copyright (C) 2021-2022 Linaro Ltd
> + */
> +#ifndef __RPMB_H__
> +#define __RPMB_H__
> +
> +#include <linux/types.h>
> +#include <linux/device.h>
> +#include <linux/notifier.h>
> +
> +/**
> + * enum rpmb_type - type of underlying storage technology
> + *
> + * @RPMB_TYPE_EMMC  : emmc (JESD84-B50.1)
> + * @RPMB_TYPE_UFS   : UFS (JESD220)
> + * @RPMB_TYPE_NVME  : NVM Express
> + */
> +enum rpmb_type {
> +       RPMB_TYPE_EMMC,
> +       RPMB_TYPE_UFS,
> +       RPMB_TYPE_NVME,
> +};
> +
> +/**
> + * struct rpmb_descr - RPMB descriptor provided by the underlying block
> device
The use of the term "rpmb descriptor" may be slightly misleading.
This is because in UFS there are various descriptors that identifies various characteristics,
e.g. device descriptor, geometry descriptor, unit descriptor etc., 
and recently UFS4.0 introduced a new descriptor - RPMB descriptor....

Thanks,
Avri