Jan Glauber | 1b27829 | 2007-02-05 21:18:22 +0100 | [diff] [blame] | 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/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 | |
| 18 | MODULE_LICENSE("GPL"); |
| 19 | MODULE_AUTHOR("Jan Glauber <jan.glauber@de.ibm.com>"); |
| 20 | MODULE_DESCRIPTION("s390 PRNG interface"); |
| 21 | |
| 22 | static int prng_chunk_size = 256; |
| 23 | module_param(prng_chunk_size, int, S_IRUSR | S_IRGRP | S_IROTH); |
| 24 | MODULE_PARM_DESC(prng_chunk_size, "PRNG read chunk size in bytes"); |
| 25 | |
| 26 | static int prng_entropy_limit = 4096; |
| 27 | module_param(prng_entropy_limit, int, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR); |
| 28 | MODULE_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 | |
| 36 | struct s390_prng_data { |
| 37 | unsigned long count; /* how many bytes were produced */ |
| 38 | char *buf; |
| 39 | }; |
| 40 | |
| 41 | static struct s390_prng_data *p; |
| 42 | |
| 43 | /* copied from libica, use a non-zero initial parameter block */ |
| 44 | static unsigned char parm_block[32] = { |
| 45 | 0x0F,0x2B,0x8E,0x63,0x8C,0x8E,0xD2,0x52,0x64,0xB7,0xA0,0x7B,0x75,0x28,0xB8,0xF4, |
| 46 | 0x75,0x5F,0xD2,0xA6,0x8D,0x97,0x11,0xFF,0x49,0xD8,0x23,0xF3,0x7E,0x21,0xEC,0xA0, |
| 47 | }; |
| 48 | |
| 49 | static int prng_open(struct inode *inode, struct file *file) |
| 50 | { |
| 51 | return nonseekable_open(inode, file); |
| 52 | } |
| 53 | |
| 54 | static 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 | |
| 68 | static 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 | |
| 86 | static 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 Perches | c2e3bba | 2008-01-26 14:11:18 +0100 | [diff] [blame] | 93 | /* nbytes can be arbitrary length, we split it into chunks */ |
Jan Glauber | 1b27829 | 2007-02-05 21:18:22 +0100 | [diff] [blame] | 94 | 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 Engelhardt | 5c81cdb | 2008-01-26 14:11:29 +0100 | [diff] [blame] | 149 | static const struct file_operations prng_fops = { |
Jan Glauber | 1b27829 | 2007-02-05 21:18:22 +0100 | [diff] [blame] | 150 | .owner = THIS_MODULE, |
| 151 | .open = &prng_open, |
| 152 | .release = NULL, |
| 153 | .read = &prng_read, |
| 154 | }; |
| 155 | |
| 156 | static struct miscdevice prng_dev = { |
| 157 | .name = "prandom", |
| 158 | .minor = MISC_DYNAMIC_MINOR, |
| 159 | .fops = &prng_fops, |
| 160 | }; |
| 161 | |
| 162 | static 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 | |
| 195 | out_buf: |
| 196 | kfree(p->buf); |
| 197 | out_free: |
| 198 | kfree(p); |
| 199 | return ret; |
| 200 | } |
| 201 | |
| 202 | static 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 | |
| 212 | module_init(prng_init); |
| 213 | module_exit(prng_exit); |