1 /*
2 * Copyright IBM Corp. 2006,2007
3 * Author(s): Jan Glauber <jan.glauber@de.ibm.com>
4 * Driver for the s390 pseudo random number generator
5 */
6 #include <linux/fs.h>
7 #include <linux/init.h>
8 #include <linux/kernel.h>
9 #include <linux/smp_lock.h>
10 #include <linux/miscdevice.h>
11 #include <linux/module.h>
12 #include <linux/moduleparam.h>
13 #include <linux/random.h>
14 #include <asm/debug.h>
15 #include <asm/uaccess.h>
16
17 #include "crypt_s390.h"
18
19 MODULE_LICENSE("GPL");
20 MODULE_AUTHOR("Jan Glauber <jan.glauber@de.ibm.com>");
21 MODULE_DESCRIPTION("s390 PRNG interface");
22
23 static int prng_chunk_size = 256;
24 module_param(prng_chunk_size, int, S_IRUSR | S_IRGRP | S_IROTH);
25 MODULE_PARM_DESC(prng_chunk_size, "PRNG read chunk size in bytes");
26
27 static int prng_entropy_limit = 4096;
28 module_param(prng_entropy_limit, int, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR);
29 MODULE_PARM_DESC(prng_entropy_limit,
30 "PRNG add entropy after that much bytes were produced");
31
32 /*
33 * Any one who considers arithmetical methods of producing random digits is,
34 * of course, in a state of sin. -- John von Neumann
35 */
36
37 struct s390_prng_data {
38 unsigned long count; /* how many bytes were produced */
39 char *buf;
40 };
41
42 static struct s390_prng_data *p;
43
44 /* copied from libica, use a non-zero initial parameter block */
45 static unsigned char parm_block[32] = {
46 0x0F,0x2B,0x8E,0x63,0x8C,0x8E,0xD2,0x52,0x64,0xB7,0xA0,0x7B,0x75,0x28,0xB8,0xF4,
47 0x75,0x5F,0xD2,0xA6,0x8D,0x97,0x11,0xFF,0x49,0xD8,0x23,0xF3,0x7E,0x21,0xEC,0xA0,
48 };
49
prng_open(struct inode * inode,struct file * file)50 static int prng_open(struct inode *inode, struct file *file)
51 {
52 cycle_kernel_lock();
53 return nonseekable_open(inode, file);
54 }
55
prng_add_entropy(void)56 static void prng_add_entropy(void)
57 {
58 __u64 entropy[4];
59 unsigned int i;
60 int ret;
61
62 for (i = 0; i < 16; i++) {
63 ret = crypt_s390_kmc(KMC_PRNG, parm_block, (char *)entropy,
64 (char *)entropy, sizeof(entropy));
65 BUG_ON(ret < 0 || ret != sizeof(entropy));
66 memcpy(parm_block, entropy, sizeof(entropy));
67 }
68 }
69
prng_seed(int nbytes)70 static void prng_seed(int nbytes)
71 {
72 char buf[16];
73 int i = 0;
74
75 BUG_ON(nbytes > 16);
76 get_random_bytes(buf, nbytes);
77
78 /* Add the entropy */
79 while (nbytes >= 8) {
80 *((__u64 *)parm_block) ^= *((__u64 *)buf+i*8);
81 prng_add_entropy();
82 i += 8;
83 nbytes -= 8;
84 }
85 prng_add_entropy();
86 }
87
prng_read(struct file * file,char __user * ubuf,size_t nbytes,loff_t * ppos)88 static ssize_t prng_read(struct file *file, char __user *ubuf, size_t nbytes,
89 loff_t *ppos)
90 {
91 int chunk, n;
92 int ret = 0;
93 int tmp;
94
95 /* nbytes can be arbitrary length, we split it into chunks */
96 while (nbytes) {
97 /* same as in extract_entropy_user in random.c */
98 if (need_resched()) {
99 if (signal_pending(current)) {
100 if (ret == 0)
101 ret = -ERESTARTSYS;
102 break;
103 }
104 schedule();
105 }
106
107 /*
108 * we lose some random bytes if an attacker issues
109 * reads < 8 bytes, but we don't care
110 */
111 chunk = min_t(int, nbytes, prng_chunk_size);
112
113 /* PRNG only likes multiples of 8 bytes */
114 n = (chunk + 7) & -8;
115
116 if (p->count > prng_entropy_limit)
117 prng_seed(8);
118
119 /* if the CPU supports PRNG stckf is present too */
120 asm volatile(".insn s,0xb27c0000,%0"
121 : "=m" (*((unsigned long long *)p->buf)) : : "cc");
122
123 /*
124 * Beside the STCKF the input for the TDES-EDE is the output
125 * of the last operation. We differ here from X9.17 since we
126 * only store one timestamp into the buffer. Padding the whole
127 * buffer with timestamps does not improve security, since
128 * successive stckf have nearly constant offsets.
129 * If an attacker knows the first timestamp it would be
130 * trivial to guess the additional values. One timestamp
131 * is therefore enough and still guarantees unique input values.
132 *
133 * Note: you can still get strict X9.17 conformity by setting
134 * prng_chunk_size to 8 bytes.
135 */
136 tmp = crypt_s390_kmc(KMC_PRNG, parm_block, p->buf, p->buf, n);
137 BUG_ON((tmp < 0) || (tmp != n));
138
139 p->count += n;
140
141 if (copy_to_user(ubuf, p->buf, chunk))
142 return -EFAULT;
143
144 nbytes -= chunk;
145 ret += chunk;
146 ubuf += chunk;
147 }
148 return ret;
149 }
150
151 static const struct file_operations prng_fops = {
152 .owner = THIS_MODULE,
153 .open = &prng_open,
154 .release = NULL,
155 .read = &prng_read,
156 };
157
158 static struct miscdevice prng_dev = {
159 .name = "prandom",
160 .minor = MISC_DYNAMIC_MINOR,
161 .fops = &prng_fops,
162 };
163
prng_init(void)164 static int __init prng_init(void)
165 {
166 int ret;
167
168 /* check if the CPU has a PRNG */
169 if (!crypt_s390_func_available(KMC_PRNG))
170 return -EOPNOTSUPP;
171
172 if (prng_chunk_size < 8)
173 return -EINVAL;
174
175 p = kmalloc(sizeof(struct s390_prng_data), GFP_KERNEL);
176 if (!p)
177 return -ENOMEM;
178 p->count = 0;
179
180 p->buf = kmalloc(prng_chunk_size, GFP_KERNEL);
181 if (!p->buf) {
182 ret = -ENOMEM;
183 goto out_free;
184 }
185
186 /* initialize the PRNG, add 128 bits of entropy */
187 prng_seed(16);
188
189 ret = misc_register(&prng_dev);
190 if (ret)
191 goto out_buf;
192 return 0;
193
194 out_buf:
195 kfree(p->buf);
196 out_free:
197 kfree(p);
198 return ret;
199 }
200
prng_exit(void)201 static void __exit prng_exit(void)
202 {
203 /* wipe me */
204 memset(p->buf, 0, prng_chunk_size);
205 kfree(p->buf);
206 kfree(p);
207
208 misc_deregister(&prng_dev);
209 }
210
211 module_init(prng_init);
212 module_exit(prng_exit);
213