path: root/drivers/crypto/atmel-ecc.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Microchip / Atmel ECC (I2C) driver.
 *
 * Copyright (c) 2017, Microchip Technology Inc.
 * Author: Tudor Ambarus <tudor.ambarus@microchip.com>
 */

#include <linux/bitrev.h>
#include <linux/crc16.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of_device.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <crypto/internal/kpp.h>
#include <crypto/ecdh.h>
#include <crypto/kpp.h>
#include "atmel-ecc.h"

/* Used for binding tfm objects to i2c clients. */
struct atmel_ecc_driver_data {
	struct list_head i2c_client_list;
	spinlock_t i2c_list_lock;
} ____cacheline_aligned;

static struct atmel_ecc_driver_data driver_data;

/**
 * atmel_ecc_i2c_client_priv - i2c_client private data
 * @client              : pointer to i2c client device
 * @i2c_client_list_node: part of i2c_client_list
 * @lock                : lock for sending i2c commands
 * @wake_token          : wake token array of zeros
 * @wake_token_sz       : size in bytes of the wake_token
 * @tfm_count           : number of active crypto transformations on i2c client
 *
 * Reads and writes from/to the i2c client are sequential. The first byte
 * transmitted to the device is treated as the byte size. Any attempt to send
 * more than this number of bytes will cause the device to not ACK those bytes.
 * After the host writes a single command byte to the input buffer, reads are
 * prohibited until after the device completes command execution. Use a mutex
 * when sending i2c commands.
 */
struct atmel_ecc_i2c_client_priv {
	struct i2c_client *client;
	struct list_head i2c_client_list_node;
	struct mutex lock;
	u8 wake_token[WAKE_TOKEN_MAX_SIZE];
	size_t wake_token_sz;
	atomic_t tfm_count ____cacheline_aligned;
};

/**
 * atmel_ecdh_ctx - transformation context
 * @client     : pointer to i2c client device
 * @fallback   : used for unsupported curves or when user wants to use its own
 *               private key.
 * @public_key : generated when calling set_secret(). It's the responsibility
 *               of the user to not call set_secret() while
 *               generate_public_key() or compute_shared_secret() are in flight.
 * @curve_id   : elliptic curve id
 * @n_sz       : size in bytes of the n prime
 * @do_fallback: true when the device doesn't support the curve or when the user
 *               wants to use its own private key.
 */
struct atmel_ecdh_ctx {
	struct i2c_client *client;
	struct crypto_kpp *fallback;
	const u8 *public_key;
	unsigned int curve_id;
	size_t n_sz;
	bool do_fallback;
};

/**
 * atmel_ecc_work_data - data structure representing the work
 * @ctx : transformation context.
 * @cbk : pointer to a callback function to be invoked upon completion of this
 *        request. This has the form:
 *        callback(struct atmel_ecc_work_data *work_data, void *areq, u8 status)
 *        where:
 *        @work_data: data structure representing the work
 *        @areq     : optional pointer to an argument passed with the original
 *                    request.
 *        @status   : status returned from the i2c client device or i2c error.
 * @areq: optional pointer to a user argument for use at callback time.
 * @work: describes the task to be executed.
 * @cmd : structure used for communicating with the device.
 */
struct atmel_ecc_work_data {
	struct atmel_ecdh_ctx *ctx;
	void (*cbk)(struct atmel_ecc_work_data *work_data, void *areq,
		    int status);
	void *areq;
	struct work_struct work;
	struct atmel_ecc_cmd cmd;
};

static u16 atmel_ecc_crc16(u16 crc, const u8 *buffer, size_t len)
{
	return cpu_to_le16(bitrev16(crc16(crc, buffer, len)));
}

/**
 * atmel_ecc_checksum() - Generate 16-bit CRC as required by ATMEL ECC.
 * CRC16 verification of the count, opcode, param1, param2 and data bytes.
 * The checksum is saved in little-endian format in the least significant
 * two bytes of the command. CRC polynomial is 0x8005 and the initial register
 * value should be zero.
 *
 * @cmd : structure used for communicating with the device.
 */
static void atmel_ecc_checksum(struct atmel_ecc_cmd *cmd)
{
	u8 *data = &cmd->count;
	size_t len = cmd->count - CRC_SIZE;
	u16 *crc16 = (u16 *)(data + len);

	*crc16 = atmel_ecc_crc16(0, data, len);
}

static void atmel_ecc_init_read_cmd(struct atmel_ecc_cmd *cmd)
{
	cmd->word_addr = COMMAND;
	cmd->opcode = OPCODE_READ;
	/*
	 * Read the word from Configuration zone that contains the lock bytes
	 * (UserExtra, Selector, LockValue, LockConfig).
	 */
	cmd->param1 = CONFIG_ZONE;
	cmd->param2 = DEVICE_LOCK_ADDR;
	cmd->count = READ_COUNT;

	atmel_ecc_checksum(cmd);

	cmd->msecs = MAX_EXEC_TIME_READ;
	cmd->rxsize = READ_RSP_SIZE;
}

static void atmel_ecc_init_genkey_cmd(struct atmel_ecc_cmd *cmd, u16 keyid)
{
	cmd->word_addr = COMMAND;
	cmd->count = GENKEY_COUNT;
	cmd->opcode = OPCODE_GENKEY;
	cmd->param1 = GENKEY_MODE_PRIVATE;
	/* a random private key will be generated and stored in slot keyID */
	cmd->param2 = cpu_to_le16(keyid);

	atmel_ecc_checksum(cmd);

	cmd->msecs = MAX_EXEC_TIME_GENKEY;
	cmd->rxsize = GENKEY_RSP_SIZE;
}

static int atmel_ecc_init_ecdh_cmd(struct atmel_ecc_cmd *cmd,
				   struct scatterlist *pubkey)
{
	size_t copied;

	cmd->word_addr = COMMAND;
	cmd->count = ECDH_COUNT;
	cmd->opcode = OPCODE_ECDH;
	cmd->param1 = ECDH_PREFIX_MODE;
	/* private key slot */
	cmd->param2 = cpu_to_le16(DATA_SLOT_2);

	/*
	 * The device only supports NIST P256 ECC keys. The public key size will
	 * always be the same. Use a macro for the key size to avoid unnecessary
	 * computations.
	 */
	copied = sg_copy_to_buffer(pubkey,
				   sg_nents_for_len(pubkey,
						    ATMEL_ECC_PUBKEY_SIZE),
				   cmd->data, ATMEL_ECC_PUBKEY_SIZE);
	if (copied != ATMEL_ECC_PUBKEY_SIZE)
		return -EINVAL;

	atmel_ecc_checksum(cmd);

	cmd->msecs = MAX_EXEC_TIME_ECDH;
	cmd->rxsize = ECDH_RSP_SIZE;

	return 0;
}

/*
 * After wake and after execution of a command, there will be error, status, or
 * result bytes in the device's output register that can be retrieved by the
 * system. When the length of that group is four bytes, the codes returned are
 * detailed in error_list.
 */
static int atmel_ecc_status(struct device *dev, u8 *status)
{
	size_t err_list_len = ARRAY_SIZE(error_list);
	int i;
	u8 err_id = status[1];

	if (*status != STATUS_SIZE)
		return 0;

	if (err_id == STATUS_WAKE_SUCCESSFUL || err_id == STATUS_NOERR)
		return 0;

	for (i = 0; i < err_list_len; i++)
		if (error_list[i].value == err_id)
			break;

	/* if err_id is not in the error_list then ignore it */
	if (i != err_list_len) {
		dev_err(dev, "%02x: %s:\n", err_id, error_list[i].error_text);
		return err_id;
	}

	return 0;
}

static int atmel_ecc_wakeup(struct i2c_client *client)
{
	struct atmel_ecc_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
	u8 status[STATUS_RSP_SIZE];
	int ret;

	/*
	 * The device ignores any levels or transitions on the SCL pin when the
	 * device is idle, asleep or during waking up. Don't check for error
	 * when waking up the device.
	 */
	i2c_master_send(client, i2c_priv->wake_token, i2c_priv->wake_token_sz);

	/*
	 * Wait to wake t