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Jan Glauber1b278292007-02-05 21:18:22 +01001/*
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/miscdevice.h>
10#include <linux/module.h>
11#include <linux/moduleparam.h>
12#include <linux/random.h>
13#include <asm/debug.h>
14#include <asm/uaccess.h>
15
16#include "crypt_s390.h"
17
18MODULE_LICENSE("GPL");
19MODULE_AUTHOR("Jan Glauber <jan.glauber@de.ibm.com>");
20MODULE_DESCRIPTION("s390 PRNG interface");
21
22static int prng_chunk_size = 256;
23module_param(prng_chunk_size, int, S_IRUSR | S_IRGRP | S_IROTH);
24MODULE_PARM_DESC(prng_chunk_size, "PRNG read chunk size in bytes");
25
26static int prng_entropy_limit = 4096;
27module_param(prng_entropy_limit, int, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR);
28MODULE_PARM_DESC(prng_entropy_limit,
29 "PRNG add entropy after that much bytes were produced");
30
31/*
32 * Any one who considers arithmetical methods of producing random digits is,
33 * of course, in a state of sin. -- John von Neumann
34 */
35
36struct s390_prng_data {
37 unsigned long count; /* how many bytes were produced */
38 char *buf;
39};
40
41static struct s390_prng_data *p;
42
43/* copied from libica, use a non-zero initial parameter block */
44static unsigned char parm_block[32] = {
450x0F,0x2B,0x8E,0x63,0x8C,0x8E,0xD2,0x52,0x64,0xB7,0xA0,0x7B,0x75,0x28,0xB8,0xF4,
460x75,0x5F,0xD2,0xA6,0x8D,0x97,0x11,0xFF,0x49,0xD8,0x23,0xF3,0x7E,0x21,0xEC,0xA0,
47};
48
49static int prng_open(struct inode *inode, struct file *file)
50{
51 return nonseekable_open(inode, file);
52}
53
54static void prng_add_entropy(void)
55{
56 __u64 entropy[4];
57 unsigned int i;
58 int ret;
59
60 for (i = 0; i < 16; i++) {
61 ret = crypt_s390_kmc(KMC_PRNG, parm_block, (char *)entropy,
62 (char *)entropy, sizeof(entropy));
63 BUG_ON(ret < 0 || ret != sizeof(entropy));
64 memcpy(parm_block, entropy, sizeof(entropy));
65 }
66}
67
68static void prng_seed(int nbytes)
69{
70 char buf[16];
71 int i = 0;
72
73 BUG_ON(nbytes > 16);
74 get_random_bytes(buf, nbytes);
75
76 /* Add the entropy */
77 while (nbytes >= 8) {
78 *((__u64 *)parm_block) ^= *((__u64 *)buf+i*8);
79 prng_add_entropy();
80 i += 8;
81 nbytes -= 8;
82 }
83 prng_add_entropy();
84}
85
86static ssize_t prng_read(struct file *file, char __user *ubuf, size_t nbytes,
87 loff_t *ppos)
88{
89 int chunk, n;
90 int ret = 0;
91 int tmp;
92
Joe Perchesc2e3bba2008-01-26 14:11:18 +010093 /* nbytes can be arbitrary length, we split it into chunks */
Jan Glauber1b278292007-02-05 21:18:22 +010094 while (nbytes) {
95 /* same as in extract_entropy_user in random.c */
96 if (need_resched()) {
97 if (signal_pending(current)) {
98 if (ret == 0)
99 ret = -ERESTARTSYS;
100 break;
101 }
102 schedule();
103 }
104
105 /*
106 * we lose some random bytes if an attacker issues
107 * reads < 8 bytes, but we don't care
108 */
109 chunk = min_t(int, nbytes, prng_chunk_size);
110
111 /* PRNG only likes multiples of 8 bytes */
112 n = (chunk + 7) & -8;
113
114 if (p->count > prng_entropy_limit)
115 prng_seed(8);
116
117 /* if the CPU supports PRNG stckf is present too */
118 asm volatile(".insn s,0xb27c0000,%0"
119 : "=m" (*((unsigned long long *)p->buf)) : : "cc");
120
121 /*
122 * Beside the STCKF the input for the TDES-EDE is the output
123 * of the last operation. We differ here from X9.17 since we
124 * only store one timestamp into the buffer. Padding the whole
125 * buffer with timestamps does not improve security, since
126 * successive stckf have nearly constant offsets.
127 * If an attacker knows the first timestamp it would be
128 * trivial to guess the additional values. One timestamp
129 * is therefore enough and still guarantees unique input values.
130 *
131 * Note: you can still get strict X9.17 conformity by setting
132 * prng_chunk_size to 8 bytes.
133 */
134 tmp = crypt_s390_kmc(KMC_PRNG, parm_block, p->buf, p->buf, n);
135 BUG_ON((tmp < 0) || (tmp != n));
136
137 p->count += n;
138
139 if (copy_to_user(ubuf, p->buf, chunk))
140 return -EFAULT;
141
142 nbytes -= chunk;
143 ret += chunk;
144 ubuf += chunk;
145 }
146 return ret;
147}
148
Jan Engelhardt5c81cdb2008-01-26 14:11:29 +0100149static const struct file_operations prng_fops = {
Jan Glauber1b278292007-02-05 21:18:22 +0100150 .owner = THIS_MODULE,
151 .open = &prng_open,
152 .release = NULL,
153 .read = &prng_read,
154};
155
156static struct miscdevice prng_dev = {
157 .name = "prandom",
158 .minor = MISC_DYNAMIC_MINOR,
159 .fops = &prng_fops,
160};
161
162static int __init prng_init(void)
163{
164 int ret;
165
166 /* check if the CPU has a PRNG */
167 if (!crypt_s390_func_available(KMC_PRNG))
168 return -EOPNOTSUPP;
169
170 if (prng_chunk_size < 8)
171 return -EINVAL;
172
173 p = kmalloc(sizeof(struct s390_prng_data), GFP_KERNEL);
174 if (!p)
175 return -ENOMEM;
176 p->count = 0;
177
178 p->buf = kmalloc(prng_chunk_size, GFP_KERNEL);
179 if (!p->buf) {
180 ret = -ENOMEM;
181 goto out_free;
182 }
183
184 /* initialize the PRNG, add 128 bits of entropy */
185 prng_seed(16);
186
187 ret = misc_register(&prng_dev);
188 if (ret) {
189 printk(KERN_WARNING
190 "Could not register misc device for PRNG.\n");
191 goto out_buf;
192 }
193 return 0;
194
195out_buf:
196 kfree(p->buf);
197out_free:
198 kfree(p);
199 return ret;
200}
201
202static void __exit prng_exit(void)
203{
204 /* wipe me */
205 memset(p->buf, 0, prng_chunk_size);
206 kfree(p->buf);
207 kfree(p);
208
209 misc_deregister(&prng_dev);
210}
211
212module_init(prng_init);
213module_exit(prng_exit);