1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Microchip / Atmel ECC (I2C) driver.
4 *
5 * Copyright (c) 2017, Microchip Technology Inc.
6 * Author: Tudor Ambarus
7 */
8
9 #include <linux/delay.h>
10 #include <linux/device.h>
11 #include <linux/err.h>
12 #include <linux/errno.h>
13 #include <linux/i2c.h>
14 #include <linux/init.h>
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/of.h>
18 #include <linux/scatterlist.h>
19 #include <linux/slab.h>
20 #include <linux/workqueue.h>
21 #include <crypto/internal/kpp.h>
22 #include <crypto/ecdh.h>
23 #include <crypto/kpp.h>
24 #include "atmel-i2c.h"
25
26 static struct atmel_ecc_driver_data driver_data;
27
28 /**
29 * struct atmel_ecdh_ctx - transformation context
30 * @client : pointer to i2c client device
31 * @fallback : used for unsupported curves or when user wants to use its own
32 * private key.
33 * @public_key : generated when calling set_secret(). It's the responsibility
34 * of the user to not call set_secret() while
35 * generate_public_key() or compute_shared_secret() are in flight.
36 * @curve_id : elliptic curve id
37 * @do_fallback: true when the device doesn't support the curve or when the user
38 * wants to use its own private key.
39 */
40 struct atmel_ecdh_ctx {
41 struct i2c_client *client;
42 struct crypto_kpp *fallback;
43 const u8 *public_key;
44 unsigned int curve_id;
45 bool do_fallback;
46 };
47
atmel_ecdh_done(struct atmel_i2c_work_data * work_data,void * areq,int status)48 static void atmel_ecdh_done(struct atmel_i2c_work_data *work_data, void *areq,
49 int status)
50 {
51 struct kpp_request *req = areq;
52 struct atmel_i2c_cmd *cmd = &work_data->cmd;
53 size_t copied, n_sz;
54
55 if (status)
56 goto free_work_data;
57
58 /* might want less than we've got */
59 n_sz = min_t(size_t, ATMEL_ECC_NIST_P256_N_SIZE, req->dst_len);
60
61 /* copy the shared secret */
62 copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst, n_sz),
63 &cmd->data[RSP_DATA_IDX], n_sz);
64 if (copied != n_sz)
65 status = -EINVAL;
66
67 /* fall through */
68 free_work_data:
69 kfree_sensitive(work_data);
70 kpp_request_complete(req, status);
71 }
72
73 /*
74 * A random private key is generated and stored in the device. The device
75 * returns the pair public key.
76 */
atmel_ecdh_set_secret(struct crypto_kpp * tfm,const void * buf,unsigned int len)77 static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
78 unsigned int len)
79 {
80 struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
81 struct atmel_i2c_cmd *cmd;
82 void *public_key;
83 struct ecdh params;
84 int ret = -ENOMEM;
85
86 /* free the old public key, if any */
87 kfree(ctx->public_key);
88 /* make sure you don't free the old public key twice */
89 ctx->public_key = NULL;
90
91 if (crypto_ecdh_decode_key(buf, len, ¶ms) < 0) {
92 dev_err(&ctx->client->dev, "crypto_ecdh_decode_key failed\n");
93 return -EINVAL;
94 }
95
96 if (params.key_size) {
97 /* fallback to ecdh software implementation */
98 ctx->do_fallback = true;
99 return crypto_kpp_set_secret(ctx->fallback, buf, len);
100 }
101
102 cmd = kmalloc(sizeof(*cmd), GFP_KERNEL);
103 if (!cmd)
104 return -ENOMEM;
105
106 /*
107 * The device only supports NIST P256 ECC keys. The public key size will
108 * always be the same. Use a macro for the key size to avoid unnecessary
109 * computations.
110 */
111 public_key = kmalloc(ATMEL_ECC_PUBKEY_SIZE, GFP_KERNEL);
112 if (!public_key)
113 goto free_cmd;
114
115 ctx->do_fallback = false;
116
117 atmel_i2c_init_genkey_cmd(cmd, DATA_SLOT_2);
118
119 ret = atmel_i2c_send_receive(ctx->client, cmd);
120 if (ret)
121 goto free_public_key;
122
123 /* save the public key */
124 memcpy(public_key, &cmd->data[RSP_DATA_IDX], ATMEL_ECC_PUBKEY_SIZE);
125 ctx->public_key = public_key;
126
127 kfree(cmd);
128 return 0;
129
130 free_public_key:
131 kfree(public_key);
132 free_cmd:
133 kfree(cmd);
134 return ret;
135 }
136
atmel_ecdh_generate_public_key(struct kpp_request * req)137 static int atmel_ecdh_generate_public_key(struct kpp_request *req)
138 {
139 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
140 struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
141 size_t copied, nbytes;
142 int ret = 0;
143
144 if (ctx->do_fallback) {
145 kpp_request_set_tfm(req, ctx->fallback);
146 return crypto_kpp_generate_public_key(req);
147 }
148
149 if (!ctx->public_key)
150 return -EINVAL;
151
152 /* might want less than we've got */
153 nbytes = min_t(size_t, ATMEL_ECC_PUBKEY_SIZE, req->dst_len);
154
155 /* public key was saved at private key generation */
156 copied = sg_copy_from_buffer(req->dst,
157 sg_nents_for_len(req->dst, nbytes),
158 ctx->public_key, nbytes);
159 if (copied != nbytes)
160 ret = -EINVAL;
161
162 return ret;
163 }
164
atmel_ecdh_compute_shared_secret(struct kpp_request * req)165 static int atmel_ecdh_compute_shared_secret(struct kpp_request *req)
166 {
167 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
168 struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
169 struct atmel_i2c_work_data *work_data;
170 gfp_t gfp;
171 int ret;
172
173 if (ctx->do_fallback) {
174 kpp_request_set_tfm(req, ctx->fallback);
175 return crypto_kpp_compute_shared_secret(req);
176 }
177
178 /* must have exactly two points to be on the curve */
179 if (req->src_len != ATMEL_ECC_PUBKEY_SIZE)
180 return -EINVAL;
181
182 gfp = (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ? GFP_KERNEL :
183 GFP_ATOMIC;
184
185 work_data = kmalloc(sizeof(*work_data), gfp);
186 if (!work_data)
187 return -ENOMEM;
188
189 work_data->ctx = ctx;
190 work_data->client = ctx->client;
191
192 ret = atmel_i2c_init_ecdh_cmd(&work_data->cmd, req->src);
193 if (ret)
194 goto free_work_data;
195
196 atmel_i2c_enqueue(work_data, atmel_ecdh_done, req);
197
198 return -EINPROGRESS;
199
200 free_work_data:
201 kfree(work_data);
202 return ret;
203 }
204
atmel_ecc_i2c_client_alloc(void)205 static struct i2c_client *atmel_ecc_i2c_client_alloc(void)
206 {
207 struct atmel_i2c_client_priv *i2c_priv, *min_i2c_priv = NULL;
208 struct i2c_client *client = ERR_PTR(-ENODEV);
209 int min_tfm_cnt = INT_MAX;
210 int tfm_cnt;
211
212 spin_lock(&driver_data.i2c_list_lock);
213
214 if (list_empty(&driver_data.i2c_client_list)) {
215 spin_unlock(&driver_data.i2c_list_lock);
216 return ERR_PTR(-ENODEV);
217 }
218
219 list_for_each_entry(i2c_priv, &driver_data.i2c_client_list,
220 i2c_client_list_node) {
221 tfm_cnt = atomic_read(&i2c_priv->tfm_count);
222 if (tfm_cnt < min_tfm_cnt) {
223 min_tfm_cnt = tfm_cnt;
224 min_i2c_priv = i2c_priv;
225 }
226 if (!min_tfm_cnt)
227 break;
228 }
229
230 if (min_i2c_priv) {
231 atomic_inc(&min_i2c_priv->tfm_count);
232 client = min_i2c_priv->client;
233 }
234
235 spin_unlock(&driver_data.i2c_list_lock);
236
237 return client;
238 }
239
atmel_ecc_i2c_client_free(struct i2c_client * client)240 static void atmel_ecc_i2c_client_free(struct i2c_client *client)
241 {
242 struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
243
244 atomic_dec(&i2c_priv->tfm_count);
245 }
246
atmel_ecdh_init_tfm(struct crypto_kpp * tfm)247 static int atmel_ecdh_init_tfm(struct crypto_kpp *tfm)
248 {
249 const char *alg = kpp_alg_name(tfm);
250 struct crypto_kpp *fallback;
251 struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
252
253 ctx->curve_id = ECC_CURVE_NIST_P256;
254 ctx->client = atmel_ecc_i2c_client_alloc();
255 if (IS_ERR(ctx->client)) {
256 pr_err("tfm - i2c_client binding failed\n");
257 return PTR_ERR(ctx->client);
258 }
259
260 fallback = crypto_alloc_kpp(alg, 0, CRYPTO_ALG_NEED_FALLBACK);
261 if (IS_ERR(fallback)) {
262 dev_err(&ctx->client->dev, "Failed to allocate transformation for '%s': %ld\n",
263 alg, PTR_ERR(fallback));
264 return PTR_ERR(fallback);
265 }
266
267 crypto_kpp_set_flags(fallback, crypto_kpp_get_flags(tfm));
268 ctx->fallback = fallback;
269
270 return 0;
271 }
272
atmel_ecdh_exit_tfm(struct crypto_kpp * tfm)273 static void atmel_ecdh_exit_tfm(struct crypto_kpp *tfm)
274 {
275 struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
276
277 kfree(ctx->public_key);
278 crypto_free_kpp(ctx->fallback);
279 atmel_ecc_i2c_client_free(ctx->client);
280 }
281
atmel_ecdh_max_size(struct crypto_kpp * tfm)282 static unsigned int atmel_ecdh_max_size(struct crypto_kpp *tfm)
283 {
284 struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
285
286 if (ctx->fallback)
287 return crypto_kpp_maxsize(ctx->fallback);
288
289 /*
290 * The device only supports NIST P256 ECC keys. The public key size will
291 * always be the same. Use a macro for the key size to avoid unnecessary
292 * computations.
293 */
294 return ATMEL_ECC_PUBKEY_SIZE;
295 }
296
297 static struct kpp_alg atmel_ecdh_nist_p256 = {
298 .set_secret = atmel_ecdh_set_secret,
299 .generate_public_key = atmel_ecdh_generate_public_key,
300 .compute_shared_secret = atmel_ecdh_compute_shared_secret,
301 .init = atmel_ecdh_init_tfm,
302 .exit = atmel_ecdh_exit_tfm,
303 .max_size = atmel_ecdh_max_size,
304 .base = {
305 .cra_flags = CRYPTO_ALG_NEED_FALLBACK,
306 .cra_name = "ecdh-nist-p256",
307 .cra_driver_name = "atmel-ecdh",
308 .cra_priority = ATMEL_ECC_PRIORITY,
309 .cra_module = THIS_MODULE,
310 .cra_ctxsize = sizeof(struct atmel_ecdh_ctx),
311 },
312 };
313
atmel_ecc_probe(struct i2c_client * client)314 static int atmel_ecc_probe(struct i2c_client *client)
315 {
316 struct atmel_i2c_client_priv *i2c_priv;
317 int ret;
318
319 ret = atmel_i2c_probe(client);
320 if (ret)
321 return ret;
322
323 i2c_priv = i2c_get_clientdata(client);
324
325 spin_lock(&driver_data.i2c_list_lock);
326 list_add_tail(&i2c_priv->i2c_client_list_node,
327 &driver_data.i2c_client_list);
328 spin_unlock(&driver_data.i2c_list_lock);
329
330 ret = crypto_register_kpp(&atmel_ecdh_nist_p256);
331 if (ret) {
332 spin_lock(&driver_data.i2c_list_lock);
333 list_del(&i2c_priv->i2c_client_list_node);
334 spin_unlock(&driver_data.i2c_list_lock);
335
336 dev_err(&client->dev, "%s alg registration failed\n",
337 atmel_ecdh_nist_p256.base.cra_driver_name);
338 } else {
339 dev_info(&client->dev, "atmel ecc algorithms registered in /proc/crypto\n");
340 }
341
342 return ret;
343 }
344
atmel_ecc_remove(struct i2c_client * client)345 static void atmel_ecc_remove(struct i2c_client *client)
346 {
347 struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
348
349 /* Return EBUSY if i2c client already allocated. */
350 if (atomic_read(&i2c_priv->tfm_count)) {
351 /*
352 * After we return here, the memory backing the device is freed.
353 * That happens no matter what the return value of this function
354 * is because in the Linux device model there is no error
355 * handling for unbinding a driver.
356 * If there is still some action pending, it probably involves
357 * accessing the freed memory.
358 */
359 dev_emerg(&client->dev, "Device is busy, expect memory corruption.\n");
360 return;
361 }
362
363 crypto_unregister_kpp(&atmel_ecdh_nist_p256);
364
365 spin_lock(&driver_data.i2c_list_lock);
366 list_del(&i2c_priv->i2c_client_list_node);
367 spin_unlock(&driver_data.i2c_list_lock);
368 }
369
370 #ifdef CONFIG_OF
371 static const struct of_device_id atmel_ecc_dt_ids[] = {
372 {
373 .compatible = "atmel,atecc508a",
374 }, {
375 /* sentinel */
376 }
377 };
378 MODULE_DEVICE_TABLE(of, atmel_ecc_dt_ids);
379 #endif
380
381 static const struct i2c_device_id atmel_ecc_id[] = {
382 { "atecc508a", 0 },
383 { }
384 };
385 MODULE_DEVICE_TABLE(i2c, atmel_ecc_id);
386
387 static struct i2c_driver atmel_ecc_driver = {
388 .driver = {
389 .name = "atmel-ecc",
390 .of_match_table = of_match_ptr(atmel_ecc_dt_ids),
391 },
392 .probe = atmel_ecc_probe,
393 .remove = atmel_ecc_remove,
394 .id_table = atmel_ecc_id,
395 };
396
atmel_ecc_init(void)397 static int __init atmel_ecc_init(void)
398 {
399 spin_lock_init(&driver_data.i2c_list_lock);
400 INIT_LIST_HEAD(&driver_data.i2c_client_list);
401 return i2c_add_driver(&atmel_ecc_driver);
402 }
403
atmel_ecc_exit(void)404 static void __exit atmel_ecc_exit(void)
405 {
406 atmel_i2c_flush_queue();
407 i2c_del_driver(&atmel_ecc_driver);
408 }
409
410 module_init(atmel_ecc_init);
411 module_exit(atmel_ecc_exit);
412
413 MODULE_AUTHOR("Tudor Ambarus");
414 MODULE_DESCRIPTION("Microchip / Atmel ECC (I2C) driver");
415 MODULE_LICENSE("GPL v2");
416
