xref: /linux/drivers/crypto/exynos-rng.c (revision 2da68a77) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * exynos-rng.c - Random Number Generator driver for the Exynos
4  *
5  * Copyright (c) 2017 Krzysztof Kozlowski <krzk@kernel.org>
6  *
7  * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
8  * Copyright (C) 2012 Samsung Electronics
9  * Jonghwa Lee <jonghwa3.lee@samsung.com>
10  */
11 
12 #include <linux/clk.h>
13 #include <linux/crypto.h>
14 #include <linux/err.h>
15 #include <linux/io.h>
16 #include <linux/module.h>
17 #include <linux/mutex.h>
18 #include <linux/of_device.h>
19 #include <linux/platform_device.h>
20 
21 #include <crypto/internal/rng.h>
22 
23 #define EXYNOS_RNG_CONTROL		0x0
24 #define EXYNOS_RNG_STATUS		0x10
25 
26 #define EXYNOS_RNG_SEED_CONF		0x14
27 #define EXYNOS_RNG_GEN_PRNG	        BIT(1)
28 
29 #define EXYNOS_RNG_SEED_BASE		0x140
30 #define EXYNOS_RNG_SEED(n)		(EXYNOS_RNG_SEED_BASE + (n * 0x4))
31 #define EXYNOS_RNG_OUT_BASE		0x160
32 #define EXYNOS_RNG_OUT(n)		(EXYNOS_RNG_OUT_BASE + (n * 0x4))
33 
34 /* EXYNOS_RNG_CONTROL bit fields */
35 #define EXYNOS_RNG_CONTROL_START	0x18
36 /* EXYNOS_RNG_STATUS bit fields */
37 #define EXYNOS_RNG_STATUS_SEED_SETTING_DONE	BIT(1)
38 #define EXYNOS_RNG_STATUS_RNG_DONE		BIT(5)
39 
40 /* Five seed and output registers, each 4 bytes */
41 #define EXYNOS_RNG_SEED_REGS		5
42 #define EXYNOS_RNG_SEED_SIZE		(EXYNOS_RNG_SEED_REGS * 4)
43 
44 enum exynos_prng_type {
45 	EXYNOS_PRNG_UNKNOWN = 0,
46 	EXYNOS_PRNG_EXYNOS4,
47 	EXYNOS_PRNG_EXYNOS5,
48 };
49 
50 /*
51  * Driver re-seeds itself with generated random numbers to hinder
52  * backtracking of the original seed.
53  *
54  * Time for next re-seed in ms.
55  */
56 #define EXYNOS_RNG_RESEED_TIME		1000
57 #define EXYNOS_RNG_RESEED_BYTES		65536
58 
59 /*
60  * In polling mode, do not wait infinitely for the engine to finish the work.
61  */
62 #define EXYNOS_RNG_WAIT_RETRIES		100
63 
64 /* Context for crypto */
65 struct exynos_rng_ctx {
66 	struct exynos_rng_dev		*rng;
67 };
68 
69 /* Device associated memory */
70 struct exynos_rng_dev {
71 	struct device			*dev;
72 	enum exynos_prng_type		type;
73 	void __iomem			*mem;
74 	struct clk			*clk;
75 	struct mutex 			lock;
76 	/* Generated numbers stored for seeding during resume */
77 	u8				seed_save[EXYNOS_RNG_SEED_SIZE];
78 	unsigned int			seed_save_len;
79 	/* Time of last seeding in jiffies */
80 	unsigned long			last_seeding;
81 	/* Bytes generated since last seeding */
82 	unsigned long			bytes_seeding;
83 };
84 
85 static struct exynos_rng_dev *exynos_rng_dev;
86 
87 static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
88 {
89 	return readl_relaxed(rng->mem + offset);
90 }
91 
92 static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
93 {
94 	writel_relaxed(val, rng->mem + offset);
95 }
96 
97 static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
98 			       const u8 *seed, unsigned int slen)
99 {
100 	u32 val;
101 	int i;
102 
103 	/* Round seed length because loop iterates over full register size */
104 	slen = ALIGN_DOWN(slen, 4);
105 
106 	if (slen < EXYNOS_RNG_SEED_SIZE)
107 		return -EINVAL;
108 
109 	for (i = 0; i < slen ; i += 4) {
110 		unsigned int seed_reg = (i / 4) % EXYNOS_RNG_SEED_REGS;
111 
112 		val = seed[i] << 24;
113 		val |= seed[i + 1] << 16;
114 		val |= seed[i + 2] << 8;
115 		val |= seed[i + 3] << 0;
116 
117 		exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(seed_reg));
118 	}
119 
120 	val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
121 	if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
122 		dev_warn(rng->dev, "Seed setting not finished\n");
123 		return -EIO;
124 	}
125 
126 	rng->last_seeding = jiffies;
127 	rng->bytes_seeding = 0;
128 
129 	return 0;
130 }
131 
132 /*
133  * Start the engine and poll for finish.  Then read from output registers
134  * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
135  * random data (EXYNOS_RNG_SEED_SIZE).
136  *
137  * On success: return 0 and store number of read bytes under 'read' address.
138  * On error: return -ERRNO.
139  */
140 static int exynos_rng_get_random(struct exynos_rng_dev *rng,
141 				 u8 *dst, unsigned int dlen,
142 				 unsigned int *read)
143 {
144 	int retry = EXYNOS_RNG_WAIT_RETRIES;
145 
146 	if (rng->type == EXYNOS_PRNG_EXYNOS4) {
147 		exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
148 				  EXYNOS_RNG_CONTROL);
149 	} else if (rng->type == EXYNOS_PRNG_EXYNOS5) {
150 		exynos_rng_writel(rng, EXYNOS_RNG_GEN_PRNG,
151 				  EXYNOS_RNG_SEED_CONF);
152 	}
153 
154 	while (!(exynos_rng_readl(rng,
155 			EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
156 		cpu_relax();
157 
158 	if (!retry)
159 		return -ETIMEDOUT;
160 
161 	/* Clear status bit */
162 	exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
163 			  EXYNOS_RNG_STATUS);
164 	*read = min_t(size_t, dlen, EXYNOS_RNG_SEED_SIZE);
165 	memcpy_fromio(dst, rng->mem + EXYNOS_RNG_OUT_BASE, *read);
166 	rng->bytes_seeding += *read;
167 
168 	return 0;
169 }
170 
171 /* Re-seed itself from time to time */
172 static void exynos_rng_reseed(struct exynos_rng_dev *rng)
173 {
174 	unsigned long next_seeding = rng->last_seeding + \
175 				     msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
176 	unsigned long now = jiffies;
177 	unsigned int read = 0;
178 	u8 seed[EXYNOS_RNG_SEED_SIZE];
179 
180 	if (time_before(now, next_seeding) &&
181 	    rng->bytes_seeding < EXYNOS_RNG_RESEED_BYTES)
182 		return;
183 
184 	if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
185 		return;
186 
187 	exynos_rng_set_seed(rng, seed, read);
188 
189 	/* Let others do some of their job. */
190 	mutex_unlock(&rng->lock);
191 	mutex_lock(&rng->lock);
192 }
193 
194 static int exynos_rng_generate(struct crypto_rng *tfm,
195 			       const u8 *src, unsigned int slen,
196 			       u8 *dst, unsigned int dlen)
197 {
198 	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
199 	struct exynos_rng_dev *rng = ctx->rng;
200 	unsigned int read = 0;
201 	int ret;
202 
203 	ret = clk_prepare_enable(rng->clk);
204 	if (ret)
205 		return ret;
206 
207 	mutex_lock(&rng->lock);
208 	do {
209 		ret = exynos_rng_get_random(rng, dst, dlen, &read);
210 		if (ret)
211 			break;
212 
213 		dlen -= read;
214 		dst += read;
215 
216 		exynos_rng_reseed(rng);
217 	} while (dlen > 0);
218 	mutex_unlock(&rng->lock);
219 
220 	clk_disable_unprepare(rng->clk);
221 
222 	return ret;
223 }
224 
225 static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
226 			   unsigned int slen)
227 {
228 	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
229 	struct exynos_rng_dev *rng = ctx->rng;
230 	int ret;
231 
232 	ret = clk_prepare_enable(rng->clk);
233 	if (ret)
234 		return ret;
235 
236 	mutex_lock(&rng->lock);
237 	ret = exynos_rng_set_seed(ctx->rng, seed, slen);
238 	mutex_unlock(&rng->lock);
239 
240 	clk_disable_unprepare(rng->clk);
241 
242 	return ret;
243 }
244 
245 static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
246 {
247 	struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);
248 
249 	ctx->rng = exynos_rng_dev;
250 
251 	return 0;
252 }
253 
254 static struct rng_alg exynos_rng_alg = {
255 	.generate		= exynos_rng_generate,
256 	.seed			= exynos_rng_seed,
257 	.seedsize		= EXYNOS_RNG_SEED_SIZE,
258 	.base			= {
259 		.cra_name		= "stdrng",
260 		.cra_driver_name	= "exynos_rng",
261 		.cra_priority		= 300,
262 		.cra_ctxsize		= sizeof(struct exynos_rng_ctx),
263 		.cra_module		= THIS_MODULE,
264 		.cra_init		= exynos_rng_kcapi_init,
265 	}
266 };
267 
268 static int exynos_rng_probe(struct platform_device *pdev)
269 {
270 	struct exynos_rng_dev *rng;
271 	int ret;
272 
273 	if (exynos_rng_dev)
274 		return -EEXIST;
275 
276 	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
277 	if (!rng)
278 		return -ENOMEM;
279 
280 	rng->type = (enum exynos_prng_type)of_device_get_match_data(&pdev->dev);
281 
282 	mutex_init(&rng->lock);
283 
284 	rng->dev = &pdev->dev;
285 	rng->clk = devm_clk_get(&pdev->dev, "secss");
286 	if (IS_ERR(rng->clk)) {
287 		dev_err(&pdev->dev, "Couldn't get clock.\n");
288 		return PTR_ERR(rng->clk);
289 	}
290 
291 	rng->mem = devm_platform_ioremap_resource(pdev, 0);
292 	if (IS_ERR(rng->mem))
293 		return PTR_ERR(rng->mem);
294 
295 	platform_set_drvdata(pdev, rng);
296 
297 	exynos_rng_dev = rng;
298 
299 	ret = crypto_register_rng(&exynos_rng_alg);
300 	if (ret) {
301 		dev_err(&pdev->dev,
302 			"Couldn't register rng crypto alg: %d\n", ret);
303 		exynos_rng_dev = NULL;
304 	}
305 
306 	return ret;
307 }
308 
309 static int exynos_rng_remove(struct platform_device *pdev)
310 {
311 	crypto_unregister_rng(&exynos_rng_alg);
312 
313 	exynos_rng_dev = NULL;
314 
315 	return 0;
316 }
317 
318 static int __maybe_unused exynos_rng_suspend(struct device *dev)
319 {
320 	struct exynos_rng_dev *rng = dev_get_drvdata(dev);
321 	int ret;
322 
323 	/* If we were never seeded then after resume it will be the same */
324 	if (!rng->last_seeding)
325 		return 0;
326 
327 	rng->seed_save_len = 0;
328 	ret = clk_prepare_enable(rng->clk);
329 	if (ret)
330 		return ret;
331 
332 	mutex_lock(&rng->lock);
333 
334 	/* Get new random numbers and store them for seeding on resume. */
335 	exynos_rng_get_random(rng, rng->seed_save, sizeof(rng->seed_save),
336 			      &(rng->seed_save_len));
337 
338 	mutex_unlock(&rng->lock);
339 
340 	dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
341 		rng->seed_save_len);
342 
343 	clk_disable_unprepare(rng->clk);
344 
345 	return 0;
346 }
347 
348 static int __maybe_unused exynos_rng_resume(struct device *dev)
349 {
350 	struct exynos_rng_dev *rng = dev_get_drvdata(dev);
351 	int ret;
352 
353 	/* Never seeded so nothing to do */
354 	if (!rng->last_seeding)
355 		return 0;
356 
357 	ret = clk_prepare_enable(rng->clk);
358 	if (ret)
359 		return ret;
360 
361 	mutex_lock(&rng->lock);
362 
363 	ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);
364 
365 	mutex_unlock(&rng->lock);
366 
367 	clk_disable_unprepare(rng->clk);
368 
369 	return ret;
370 }
371 
372 static SIMPLE_DEV_PM_OPS(exynos_rng_pm_ops, exynos_rng_suspend,
373 			 exynos_rng_resume);
374 
375 static const struct of_device_id exynos_rng_dt_match[] = {
376 	{
377 		.compatible = "samsung,exynos4-rng",
378 		.data = (const void *)EXYNOS_PRNG_EXYNOS4,
379 	}, {
380 		.compatible = "samsung,exynos5250-prng",
381 		.data = (const void *)EXYNOS_PRNG_EXYNOS5,
382 	},
383 	{ },
384 };
385 MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
386 
387 static struct platform_driver exynos_rng_driver = {
388 	.driver		= {
389 		.name	= "exynos-rng",
390 		.pm	= &exynos_rng_pm_ops,
391 		.of_match_table = exynos_rng_dt_match,
392 	},
393 	.probe		= exynos_rng_probe,
394 	.remove		= exynos_rng_remove,
395 };
396 
397 module_platform_driver(exynos_rng_driver);
398 
399 MODULE_DESCRIPTION("Exynos H/W Random Number Generator driver");
400 MODULE_AUTHOR("Krzysztof Kozlowski <krzk@kernel.org>");
401 MODULE_LICENSE("GPL v2");
402