1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * s390 TRNG device driver
4 *
5 * Driver for the TRNG (true random number generation) command
6 * available via CPACF extension MSA 7 on the s390 arch.
7
8 * Copyright IBM Corp. 2017
9 * Author(s): Harald Freudenberger <freude@de.ibm.com>
10 */
11
12#define KMSG_COMPONENT "trng"
13#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
14
15#include <linux/hw_random.h>
16#include <linux/kernel.h>
17#include <linux/module.h>
18#include <linux/cpufeature.h>
19#include <linux/miscdevice.h>
20#include <linux/debugfs.h>
21#include <linux/atomic.h>
22#include <linux/random.h>
23#include <linux/sched/signal.h>
24#include <asm/debug.h>
25#include <asm/cpacf.h>
26
27MODULE_LICENSE("GPL v2");
28MODULE_AUTHOR("IBM Corporation");
29MODULE_DESCRIPTION("s390 CPACF TRNG device driver");
30
31
32/* trng related debug feature things */
33
34static debug_info_t *debug_info;
35
36#define DEBUG_DBG(...)	debug_sprintf_event(debug_info, 6, ##__VA_ARGS__)
37#define DEBUG_INFO(...) debug_sprintf_event(debug_info, 5, ##__VA_ARGS__)
38#define DEBUG_WARN(...) debug_sprintf_event(debug_info, 4, ##__VA_ARGS__)
39#define DEBUG_ERR(...)	debug_sprintf_event(debug_info, 3, ##__VA_ARGS__)
40
41
42/* trng helpers */
43
44static atomic64_t trng_dev_counter = ATOMIC64_INIT(0);
45static atomic64_t trng_hwrng_counter = ATOMIC64_INIT(0);
46
47
48/* file io functions */
49
50static int trng_open(struct inode *inode, struct file *file)
51{
52	return nonseekable_open(inode, file);
53}
54
55static ssize_t trng_read(struct file *file, char __user *ubuf,
56			 size_t nbytes, loff_t *ppos)
57{
58	u8 buf[32];
59	u8 *p = buf;
60	unsigned int n;
61	ssize_t ret = 0;
62
63	/*
64	 * use buf for requests <= sizeof(buf),
65	 * otherwise allocate one page and fetch
66	 * pagewise.
67	 */
68
69	if (nbytes > sizeof(buf)) {
70		p = (u8 *) __get_free_page(GFP_KERNEL);
71		if (!p)
72			return -ENOMEM;
73	}
74
75	while (nbytes) {
76		if (need_resched()) {
77			if (signal_pending(current)) {
78				if (ret == 0)
79					ret = -ERESTARTSYS;
80				break;
81			}
82			schedule();
83		}
84		n = nbytes > PAGE_SIZE ? PAGE_SIZE : nbytes;
85		cpacf_trng(NULL, 0, p, n);
86		atomic64_add(n, &trng_dev_counter);
87		if (copy_to_user(ubuf, p, n)) {
88			ret = -EFAULT;
89			break;
90		}
91		nbytes -= n;
92		ubuf += n;
93		ret += n;
94	}
95
96	if (p != buf)
97		free_page((unsigned long) p);
98
99	DEBUG_DBG("trng_read()=%zd\n", ret);
100	return ret;
101}
102
103
104/* sysfs */
105
106static ssize_t trng_counter_show(struct device *dev,
107				 struct device_attribute *attr, char *buf)
108{
109	u64 dev_counter = atomic64_read(&trng_dev_counter);
110	u64 hwrng_counter = atomic64_read(&trng_hwrng_counter);
111#if IS_ENABLED(CONFIG_ARCH_RANDOM)
112	u64 arch_counter = atomic64_read(&s390_arch_random_counter);
113
114	return snprintf(buf, PAGE_SIZE,
115			"trng:  %llu\n"
116			"hwrng: %llu\n"
117			"arch:  %llu\n"
118			"total: %llu\n",
119			dev_counter, hwrng_counter, arch_counter,
120			dev_counter + hwrng_counter + arch_counter);
121#else
122	return snprintf(buf, PAGE_SIZE,
123			"trng:  %llu\n"
124			"hwrng: %llu\n"
125			"total: %llu\n",
126			dev_counter, hwrng_counter,
127			dev_counter + hwrng_counter);
128#endif
129}
130static DEVICE_ATTR(byte_counter, 0444, trng_counter_show, NULL);
131
132static struct attribute *trng_dev_attrs[] = {
133	&dev_attr_byte_counter.attr,
134	NULL
135};
136
137static const struct attribute_group trng_dev_attr_group = {
138	.attrs = trng_dev_attrs
139};
140
141static const struct attribute_group *trng_dev_attr_groups[] = {
142	&trng_dev_attr_group,
143	NULL
144};
145
146static const struct file_operations trng_fops = {
147	.owner		= THIS_MODULE,
148	.open		= &trng_open,
149	.release	= NULL,
150	.read		= &trng_read,
151	.llseek		= noop_llseek,
152};
153
154static struct miscdevice trng_dev = {
155	.name	= "trng",
156	.minor	= MISC_DYNAMIC_MINOR,
157	.mode	= 0444,
158	.fops	= &trng_fops,
159	.groups = trng_dev_attr_groups,
160};
161
162
163/* hwrng_register */
164
165static inline void _trng_hwrng_read(u8 *buf, size_t len)
166{
167	cpacf_trng(NULL, 0, buf, len);
168	atomic64_add(len, &trng_hwrng_counter);
169}
170
171static int trng_hwrng_data_read(struct hwrng *rng, u32 *data)
172{
173	size_t len = sizeof(*data);
174
175	_trng_hwrng_read((u8 *) data, len);
176
177	DEBUG_DBG("trng_hwrng_data_read()=%zu\n", len);
178
179	return len;
180}
181
182static int trng_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
183{
184	size_t len = max <= PAGE_SIZE ? max : PAGE_SIZE;
185
186	_trng_hwrng_read((u8 *) data, len);
187
188	DEBUG_DBG("trng_hwrng_read()=%zu\n", len);
189
190	return len;
191}
192
193/*
194 * hwrng register struct
195 * The trng is suppost to have 100% entropy, and thus
196 * we register with a very high quality value.
197 */
198static struct hwrng trng_hwrng_dev = {
199	.name		= "s390-trng",
200	.data_read	= trng_hwrng_data_read,
201	.read		= trng_hwrng_read,
202	.quality	= 999,
203};
204
205
206/* init and exit */
207
208static void __init trng_debug_init(void)
209{
210	debug_info = debug_register("trng", 1, 1, 4 * sizeof(long));
211	debug_register_view(debug_info, &debug_sprintf_view);
212	debug_set_level(debug_info, 3);
213}
214
215static void trng_debug_exit(void)
216{
217	debug_unregister(debug_info);
218}
219
220static int __init trng_init(void)
221{
222	int ret;
223
224	trng_debug_init();
225
226	/* check if subfunction CPACF_PRNO_TRNG is available */
227	if (!cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG)) {
228		DEBUG_INFO("trng_init CPACF_PRNO_TRNG not available\n");
229		ret = -ENODEV;
230		goto out_dbg;
231	}
232
233	ret = misc_register(&trng_dev);
234	if (ret) {
235		DEBUG_WARN("trng_init misc_register() failed rc=%d\n", ret);
236		goto out_dbg;
237	}
238
239	ret = hwrng_register(&trng_hwrng_dev);
240	if (ret) {
241		DEBUG_WARN("trng_init hwrng_register() failed rc=%d\n", ret);
242		goto out_misc;
243	}
244
245	DEBUG_DBG("trng_init successful\n");
246
247	return 0;
248
249out_misc:
250	misc_deregister(&trng_dev);
251out_dbg:
252	trng_debug_exit();
253	return ret;
254}
255
256static void __exit trng_exit(void)
257{
258	hwrng_unregister(&trng_hwrng_dev);
259	misc_deregister(&trng_dev);
260	trng_debug_exit();
261}
262
263module_cpu_feature_match(MSA, trng_init);
264module_exit(trng_exit);
265