aboutsummaryrefslogtreecommitdiff
path: root/drivers/crypto/atmel-ecc.c
blob: 9bd8e5167be34bfc9ad67381f45853664a580c75 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
// 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/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-i2c.h"

static struct atmel_ecc_driver_data driver_data;

/**
 * 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;
};

static void atmel_ecdh_done(struct atmel_i2c_work_data *work_data, void *areq,
			    int status)
{
	struct kpp_request *req = areq;
	struct atmel_ecdh_ctx *ctx = work_data->ctx;
	struct atmel_i2c_cmd *cmd = &work_data->cmd;
	size_t copied, n_sz;

	if (status)
		goto free_work_data;

	/* might want less than we've got */
	n_sz = min_t(size_t, ctx->n_sz, req->dst_len);

	/* copy the shared secret */
	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst, n_sz),
				     &cmd->data[RSP_DATA_IDX], n_sz);
	if (copied != n_sz)
		status = -EINVAL;

	/* fall through */
free_work_data:
	kfree_sensitive(work_data);
	kpp_request_complete(req, status);
}

static unsigned int atmel_ecdh_supported_curve(unsigned int curve_id)
{
	if (curve_id == ECC_CURVE_NIST_P256)
		return ATMEL_ECC_NIST_P256_N_SIZE;

	return 0;
}

/*
 * A random private key is generated and stored in the device. The device
 * returns the pair public key.
 */
static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
				 unsigned int len)
{
	struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
	struct atmel_i2c_cmd *cmd;
	void *public_key;
	struct ecdh params;
	int ret = -ENOMEM;

	/* free the old public key, if any */
	kfree(ctx->public_key);
	/* make sure you don't free the old public key twice */
	ctx->public_key = NULL;

	if (crypto_ecdh_decode_key(buf, len, &params) < 0) {
		dev_err(&ctx->client->dev, "crypto_ecdh_decode_key failed\n");
		return -EINVAL;
	}

	ctx->n_sz = atmel_ecdh_supported_curve(params.curve_id);
	if (!ctx->n_sz || params.key_size) {
		/* fallback to ecdh software implementation */
		ctx->do_fallback = true;
		return crypto_kpp_set_secret(ctx->fallback, buf, len);
	}

	cmd = kmalloc(sizeof(*cmd), GFP_KERNEL);
	if (!cmd)
		return -ENOMEM;

	/*
	 * 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.
	 */
	public_key = kmalloc(ATMEL_ECC_PUBKEY_SIZE, GFP_KERNEL);
	if (!public_key)
		goto free_cmd;

	ctx->do_fallback = false;
	ctx->curve_id = params.curve_id;

	atmel_i2c_init_genkey_cmd(cmd, DATA_SLOT_2);

	ret = atmel_i2c_send_receive(ctx->client, cmd);
	if (ret)
		goto free_public_key;

	/* save the public key */
	memcpy(public_key, &cmd->data[RSP_DATA_IDX], ATMEL_ECC_PUBKEY_SIZE);
	ctx->public_key = public_key;

	kfree(cmd);
	return 0;

free_public_key:
	kfree(public_key);
free_cmd:
	kfree(cmd);
	return ret;
}

static int atmel_ecdh_generate_public_key(struct kpp_request *req)
{
	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
	struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
	size_t copied, nbytes;
	int ret = 0;

	if (ctx->do_fallback) {
		kpp_request_set_tfm(req, ctx->fallback);
		return crypto_kpp_generate_public_key(req);
	}

	if (!ctx->public_key)
		return -EINVAL;

	/* might want less than we've got */
	nbytes = min_t(size_t, ATMEL_ECC_PUBKEY_SIZE, req->dst_len);

	/* public key was saved at private key generation */
	copied = sg_copy_from_buffer(req->dst,
				     sg_nents_for_len(req->dst, nbytes),
				     ctx->public_key, nbytes);
	if (copied != nbytes)
		ret = -EINVAL;

	return ret;
}

static int atmel_ecdh_compute_shared_secret(struct kpp_request *req)
{
	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
	struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
	struct atmel_i2c_work_data *work_data;
	gfp_t gfp;
	int ret;

	if (ctx->do_fallback) {
		kpp_request_set_tfm(req, ctx->fallback);
		return crypto_kpp_compute_shared_secret(req);
	}

	/* must have exactly two points to be on the curve */
	if (req->src_len != ATMEL_ECC_PUBKEY_SIZE)
		return -EINVAL;

	gfp = (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ? GFP_KERNEL :
							     GFP_ATOMIC;

	work_data = kmalloc(sizeof(*work_data), gfp);
	if (!work_data)
		return -ENOMEM;

	work_data->ctx = ctx;
	work_data->client = ctx->client;

	ret = atmel_i2c_init_ecdh_cmd(&work_data->cmd, req->src);
	if (ret)
		goto free_work_data;

	atmel_i2c_enqueue(work_data, atmel_ecdh_done, req);

	return -EINPROGRESS;

free_work_data:
	kfree(work_data);
	return ret;
}

static struct i2c_client *atmel_ecc_i2c_client_alloc(void)
{
	struct atmel_i2c_client_priv *i2c_priv, *min_i2c_priv = NULL;
	struct i2c_client *client = ERR_PTR(-ENODEV);
	int min_tfm_cnt = INT_MAX;
	int tfm_cnt;

	spin_lock(&driver_data.i2c_list_lock);

	if (list_empty(&driver_data.i2c_client_list)) {
		spin_unlock(&driver_data.i2c_list_lock);
		return ERR_PTR(-ENODEV);
	}

	list_for_each_entry(i2c_priv, &driver_data.i2c_client_list,
			    i2c_client_list_node) {
		tfm_cnt = atomic_read(&i2c_priv->tfm_count);
		if (tfm_cnt < min_tfm_cnt) {
			min_tfm_cnt = tfm_cnt;
			min_i2c_priv = i2c_priv;
		}
		if (!min_tfm_cnt)
			break;
	}

	if (min_i2c_priv) {
		atomic_inc(&min_i2c_priv->tfm_count);
		client = min_i2c_priv->client;
	}

	spin_unlock(&driver_data.i2c_list_lock);

	return client;
}

static void atmel_ecc_i2c_client_free(struct i2c_client *client)
{
	struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);

	atomic_dec(&i2c_priv->tfm_count);
}

static int atmel_ecdh_init_tfm(struct crypto_kpp *tfm)
{
	const char *alg = kpp_alg_name(tfm);
	struct crypto_kpp *fallback;
	struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);

	ctx->client = atmel_ecc_i2c_client_alloc();
	if (IS_ERR(ctx->client)) {
		pr_err("tfm - i2c_client binding failed\n");
		return PTR_ERR(ctx->client);
	}

	fallback = crypto_alloc_kpp(alg, 0, CRYPTO_ALG_NEED_FALLBACK);
	if (IS_ERR(fallback)) {
		dev_err(&ctx->client->dev, "Failed to allocate transformation for '%s': %ld\n",
			alg, PTR_ERR(fallback));
		return PTR_ERR(fallback);
	}

	crypto_kpp_set_flags(fallback, crypto_kpp_get_flags(tfm));
	ctx->fallback = fallback;

	return 0;
}

static void atmel_ecdh_exit_tfm(struct crypto_kpp *tfm)
{
	struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);

	kfree(ctx->public_key);
	crypto_free_kpp(ctx->fallback);
	atmel_ecc_i2c_client_free(ctx->client);
}

static unsigned int atmel_ecdh_max_size(struct crypto_kpp *tfm)
{
	struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);

	if (ctx->fallback)
		return crypto_kpp_maxsize(ctx->fallback);

	/*
	 * 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.
	 */
	return ATMEL_ECC_PUBKEY_SIZE;
}

static struct kpp_alg atmel_ecdh = {
	.set_secret = atmel_ecdh_set_secret,
	.generate_public_key = atmel_ecdh_generate_public_key,
	.compute_shared_secret = atmel_ecdh_compute_shared_secret,
	.init = atmel_ecdh_init_tfm,
	.exit = atmel_ecdh_exit_tfm,
	.max_size = atmel_ecdh_max_size,
	.base = {
		.cra_flags = CRYPTO_ALG_NEED_FALLBACK,
		.cra_name = "ecdh",
		.cra_driver_name = "atmel-ecdh",
		.cra_priority = ATMEL_ECC_PRIORITY,
		.cra_module = THIS_MODULE,
		.cra_ctxsize = sizeof(struct atmel_ecdh_ctx),
	},
};

static int atmel_ecc_probe(struct i2c_client *client,
			   const struct i2c_device_id *id)
{
	struct atmel_i2c_client_priv *i2c_priv;
	int ret;

	ret = atmel_i2c_probe(client, id);
	if (ret)
		return ret;

	i2c_priv = i2c_get_clientdata(client);

	spin_lock(&driver_data.i2c_list_lock);
	list_add_tail(&i2c_priv->i2c_client_list_node,
		      &driver_data.i2c_client_list);
	spin_unlock(&driver_data.i2c_list_lock);

	ret = crypto_register_kpp(&atmel_ecdh);
	if (ret) {
		spin_lock(&driver_data.i2c_list_lock);
		list_del(&i2c_priv->i2c_client_list_node);
		spin_unlock(&driver_data.i2c_list_lock);

		dev_err(&client->dev, "%s alg registration failed\n",
			atmel_ecdh.base.cra_driver_name);
	} else {
		dev_info(&client->dev, "atmel ecc algorithms registered in /proc/crypto\n");
	}

	return ret;
}

static int atmel_ecc_remove(struct i2c_client *client)
{
	struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);

	/* Return EBUSY if i2c client already allocated. */
	if (atomic_read(&i2c_priv->tfm_count)) {
		dev_err(&client->dev, "Device is busy\n");
		return -EBUSY;
	}

	crypto_unregister_kpp(&atmel_ecdh);

	spin_lock(&driver_data.i2c_list_lock);
	list_del(&i2c_priv->i2c_client_list_node);
	spin_unlock(&driver_data.i2c_list_lock);

	return 0;
}

#ifdef CONFIG_OF
static const struct of_device_id atmel_ecc_dt_ids[] = {
	{
		.compatible = "atmel,atecc508a",
	}, {
		/* sentinel */
	}
};
MODULE_DEVICE_TABLE(of, atmel_ecc_dt_ids);
#endif

static const struct i2c_device_id atmel_ecc_id[] = {
	{ "atecc508a", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, atmel_ecc_id);

static struct i2c_driver atmel_ecc_driver = {
	.driver = {
		.name	= "atmel-ecc",
		.of_match_table = of_match_ptr(atmel_ecc_dt_ids),
	},
	.probe		= atmel_ecc_probe,
	.remove		= atmel_ecc_remove,
	.id_table	= atmel_ecc_id,
};

static int __init atmel_ecc_init(void)
{
	spin_lock_init(&driver_data.i2c_list_lock);
	INIT_LIST_HEAD(&driver_data.i2c_client_list);
	return i2c_add_driver(&atmel_ecc_driver);
}

static void __exit atmel_ecc_exit(void)
{
	flush_scheduled_work();
	i2c_del_driver(&atmel_ecc_driver);
}

module_init(atmel_ecc_init);
module_exit(atmel_ecc_exit);

MODULE_AUTHOR("Tudor Ambarus <tudor.ambarus@microchip.com>");
MODULE_DESCRIPTION("Microchip / Atmel ECC (I2C) driver");
MODULE_LICENSE("GPL v2");