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 #include <asm/archrandom.h>
27 
28 MODULE_LICENSE("GPL v2");
29 MODULE_AUTHOR("IBM Corporation");
30 MODULE_DESCRIPTION("s390 CPACF TRNG device driver");
31 
32 
33 /* trng related debug feature things */
34 
35 static debug_info_t *debug_info;
36 
37 #define DEBUG_DBG(...)	debug_sprintf_event(debug_info, 6, ##__VA_ARGS__)
38 #define DEBUG_INFO(...) debug_sprintf_event(debug_info, 5, ##__VA_ARGS__)
39 #define DEBUG_WARN(...) debug_sprintf_event(debug_info, 4, ##__VA_ARGS__)
40 #define DEBUG_ERR(...)	debug_sprintf_event(debug_info, 3, ##__VA_ARGS__)
41 
42 
43 /* trng helpers */
44 
45 static atomic64_t trng_dev_counter = ATOMIC64_INIT(0);
46 static atomic64_t trng_hwrng_counter = ATOMIC64_INIT(0);
47 
48 
49 /* file io functions */
50 
51 static int trng_open(struct inode *inode, struct file *file)
52 {
53 	return nonseekable_open(inode, file);
54 }
55 
56 static ssize_t trng_read(struct file *file, char __user *ubuf,
57 			 size_t nbytes, loff_t *ppos)
58 {
59 	u8 buf[32];
60 	u8 *p = buf;
61 	unsigned int n;
62 	ssize_t ret = 0;
63 
64 	/*
65 	 * use buf for requests <= sizeof(buf),
66 	 * otherwise allocate one page and fetch
67 	 * pagewise.
68 	 */
69 
70 	if (nbytes > sizeof(buf)) {
71 		p = (u8 *) __get_free_page(GFP_KERNEL);
72 		if (!p)
73 			return -ENOMEM;
74 	}
75 
76 	while (nbytes) {
77 		if (need_resched()) {
78 			if (signal_pending(current)) {
79 				if (ret == 0)
80 					ret = -ERESTARTSYS;
81 				break;
82 			}
83 			schedule();
84 		}
85 		n = nbytes > PAGE_SIZE ? PAGE_SIZE : nbytes;
86 		cpacf_trng(NULL, 0, p, n);
87 		atomic64_add(n, &trng_dev_counter);
88 		if (copy_to_user(ubuf, p, n)) {
89 			ret = -EFAULT;
90 			break;
91 		}
92 		nbytes -= n;
93 		ubuf += n;
94 		ret += n;
95 	}
96 
97 	if (p != buf)
98 		free_page((unsigned long) p);
99 
100 	DEBUG_DBG("trng_read()=%zd\n", ret);
101 	return ret;
102 }
103 
104 
105 /* sysfs */
106 
107 static ssize_t trng_counter_show(struct device *dev,
108 				 struct device_attribute *attr, char *buf)
109 {
110 	u64 dev_counter = atomic64_read(&trng_dev_counter);
111 	u64 hwrng_counter = atomic64_read(&trng_hwrng_counter);
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 }
122 static DEVICE_ATTR(byte_counter, 0444, trng_counter_show, NULL);
123 
124 static struct attribute *trng_dev_attrs[] = {
125 	&dev_attr_byte_counter.attr,
126 	NULL
127 };
128 
129 static const struct attribute_group trng_dev_attr_group = {
130 	.attrs = trng_dev_attrs
131 };
132 
133 static const struct attribute_group *trng_dev_attr_groups[] = {
134 	&trng_dev_attr_group,
135 	NULL
136 };
137 
138 static const struct file_operations trng_fops = {
139 	.owner		= THIS_MODULE,
140 	.open		= &trng_open,
141 	.release	= NULL,
142 	.read		= &trng_read,
143 	.llseek		= noop_llseek,
144 };
145 
146 static struct miscdevice trng_dev = {
147 	.name	= "trng",
148 	.minor	= MISC_DYNAMIC_MINOR,
149 	.mode	= 0444,
150 	.fops	= &trng_fops,
151 	.groups = trng_dev_attr_groups,
152 };
153 
154 
155 /* hwrng_register */
156 
157 static inline void _trng_hwrng_read(u8 *buf, size_t len)
158 {
159 	cpacf_trng(NULL, 0, buf, len);
160 	atomic64_add(len, &trng_hwrng_counter);
161 }
162 
163 static int trng_hwrng_data_read(struct hwrng *rng, u32 *data)
164 {
165 	size_t len = sizeof(*data);
166 
167 	_trng_hwrng_read((u8 *) data, len);
168 
169 	DEBUG_DBG("trng_hwrng_data_read()=%zu\n", len);
170 
171 	return len;
172 }
173 
174 static int trng_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
175 {
176 	size_t len = max <= PAGE_SIZE ? max : PAGE_SIZE;
177 
178 	_trng_hwrng_read((u8 *) data, len);
179 
180 	DEBUG_DBG("trng_hwrng_read()=%zu\n", len);
181 
182 	return len;
183 }
184 
185 /*
186  * hwrng register struct
187  * The trng is supposed to have 100% entropy, and thus we register with a very
188  * high quality value. If we ever have a better driver in the future, we should
189  * change this value again when we merge this driver.
190  */
191 static struct hwrng trng_hwrng_dev = {
192 	.name		= "s390-trng",
193 	.data_read	= trng_hwrng_data_read,
194 	.read		= trng_hwrng_read,
195 };
196 
197 
198 /* init and exit */
199 
200 static void __init trng_debug_init(void)
201 {
202 	debug_info = debug_register("trng", 1, 1, 4 * sizeof(long));
203 	debug_register_view(debug_info, &debug_sprintf_view);
204 	debug_set_level(debug_info, 3);
205 }
206 
207 static void trng_debug_exit(void)
208 {
209 	debug_unregister(debug_info);
210 }
211 
212 static int __init trng_init(void)
213 {
214 	int ret;
215 
216 	trng_debug_init();
217 
218 	/* check if subfunction CPACF_PRNO_TRNG is available */
219 	if (!cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG)) {
220 		DEBUG_INFO("trng_init CPACF_PRNO_TRNG not available\n");
221 		ret = -ENODEV;
222 		goto out_dbg;
223 	}
224 
225 	ret = misc_register(&trng_dev);
226 	if (ret) {
227 		DEBUG_WARN("trng_init misc_register() failed rc=%d\n", ret);
228 		goto out_dbg;
229 	}
230 
231 	ret = hwrng_register(&trng_hwrng_dev);
232 	if (ret) {
233 		DEBUG_WARN("trng_init hwrng_register() failed rc=%d\n", ret);
234 		goto out_misc;
235 	}
236 
237 	DEBUG_DBG("trng_init successful\n");
238 
239 	return 0;
240 
241 out_misc:
242 	misc_deregister(&trng_dev);
243 out_dbg:
244 	trng_debug_exit();
245 	return ret;
246 }
247 
248 static void __exit trng_exit(void)
249 {
250 	hwrng_unregister(&trng_hwrng_dev);
251 	misc_deregister(&trng_dev);
252 	trng_debug_exit();
253 }
254 
255 module_cpu_feature_match(S390_CPU_FEATURE_MSA, trng_init);
256 module_exit(trng_exit);
257