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 
27 MODULE_LICENSE("GPL v2");
28 MODULE_AUTHOR("IBM Corporation");
29 MODULE_DESCRIPTION("s390 CPACF TRNG device driver");
30 
31 
32 /* trng related debug feature things */
33 
34 static 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 
44 static atomic64_t trng_dev_counter = ATOMIC64_INIT(0);
45 static atomic64_t trng_hwrng_counter = ATOMIC64_INIT(0);
46 
47 
48 /* file io functions */
49 
50 static int trng_open(struct inode *inode, struct file *file)
51 {
52 	return nonseekable_open(inode, file);
53 }
54 
55 static 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 
106 static 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 sysfs_emit(buf,
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 sysfs_emit(buf,
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 }
130 static DEVICE_ATTR(byte_counter, 0444, trng_counter_show, NULL);
131 
132 static struct attribute *trng_dev_attrs[] = {
133 	&dev_attr_byte_counter.attr,
134 	NULL
135 };
136 
137 static const struct attribute_group trng_dev_attr_group = {
138 	.attrs = trng_dev_attrs
139 };
140 
141 static const struct attribute_group *trng_dev_attr_groups[] = {
142 	&trng_dev_attr_group,
143 	NULL
144 };
145 
146 static 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 
154 static 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 
165 static 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 
171 static 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 
182 static 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 supposed to have 100% entropy, and thus we register with a very
196  * high quality value. If we ever have a better driver in the future, we should
197  * change this value again when we merge this driver.
198  */
199 static struct hwrng trng_hwrng_dev = {
200 	.name		= "s390-trng",
201 	.data_read	= trng_hwrng_data_read,
202 	.read		= trng_hwrng_read,
203 	.quality	= 1024,
204 };
205 
206 
207 /* init and exit */
208 
209 static void __init trng_debug_init(void)
210 {
211 	debug_info = debug_register("trng", 1, 1, 4 * sizeof(long));
212 	debug_register_view(debug_info, &debug_sprintf_view);
213 	debug_set_level(debug_info, 3);
214 }
215 
216 static void trng_debug_exit(void)
217 {
218 	debug_unregister(debug_info);
219 }
220 
221 static int __init trng_init(void)
222 {
223 	int ret;
224 
225 	trng_debug_init();
226 
227 	/* check if subfunction CPACF_PRNO_TRNG is available */
228 	if (!cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG)) {
229 		DEBUG_INFO("trng_init CPACF_PRNO_TRNG not available\n");
230 		ret = -ENODEV;
231 		goto out_dbg;
232 	}
233 
234 	ret = misc_register(&trng_dev);
235 	if (ret) {
236 		DEBUG_WARN("trng_init misc_register() failed rc=%d\n", ret);
237 		goto out_dbg;
238 	}
239 
240 	ret = hwrng_register(&trng_hwrng_dev);
241 	if (ret) {
242 		DEBUG_WARN("trng_init hwrng_register() failed rc=%d\n", ret);
243 		goto out_misc;
244 	}
245 
246 	DEBUG_DBG("trng_init successful\n");
247 
248 	return 0;
249 
250 out_misc:
251 	misc_deregister(&trng_dev);
252 out_dbg:
253 	trng_debug_exit();
254 	return ret;
255 }
256 
257 static void __exit trng_exit(void)
258 {
259 	hwrng_unregister(&trng_hwrng_dev);
260 	misc_deregister(&trng_dev);
261 	trng_debug_exit();
262 }
263 
264 module_cpu_feature_match(MSA, trng_init);
265 module_exit(trng_exit);
266