arch/s390/crypto/prng.c

   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 <linux/slab.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
  50 static int prng_open(struct inode *inode, struct file *file)
  51 {
  52         return nonseekable_open(inode, file);
  53 }
  54
  55 static void prng_add_entropy(void)
  56 {
  57         __u64 entropy[4];
  58         unsigned int i;
  59         int ret;
  60
  61         for (i = 0; i < 16; i++) {
  62                 ret = crypt_s390_kmc(KMC_PRNG, parm_block, (char *)entropy,
  63                                      (char *)entropy, sizeof(entropy));
  64                 BUG_ON(ret < 0 || ret != sizeof(entropy));
  65                 memcpy(parm_block, entropy, sizeof(entropy));
  66         }
  67 }
  68
  69 static void prng_seed(int nbytes)
  70 {
  71         char buf[16];
  72         int i = 0;
  73
  74         BUG_ON(nbytes > 16);
  75         get_random_bytes(buf, nbytes);
  76
  77         /* Add the entropy */
  78         while (nbytes >= 8) {
  79                 *((__u64 *)parm_block) ^= *((__u64 *)(buf+i));
  80                 prng_add_entropy();
  81                 i += 8;
  82                 nbytes -= 8;
  83         }
  84         prng_add_entropy();
  85 }
  86
  87 static ssize_t prng_read(struct file *file, char __user *ubuf, size_t nbytes,
  88                          loff_t *ppos)
  89 {
  90         int chunk, n;
  91         int ret = 0;
  92         int tmp;
  93
  94         /* nbytes can be arbitrary length, we split it into chunks */
  95         while (nbytes) {
  96                 /* same as in extract_entropy_user in random.c */
  97                 if (need_resched()) {
  98                         if (signal_pending(current)) {
  99                                 if (ret == 0)
 100                                         ret = -ERESTARTSYS;
 101                                 break;
 102                         }
 103                         schedule();
 104                 }
 105
 106                 /*
 107                  * we lose some random bytes if an attacker issues
 108                  * reads < 8 bytes, but we don't care
 109                  */
 110                 chunk = min_t(int, nbytes, prng_chunk_size);
 111
 112                 /* PRNG only likes multiples of 8 bytes */
 113                 n = (chunk + 7) & -8;
 114
 115                 if (p->count > prng_entropy_limit)
 116                         prng_seed(8);
 117
 118                 /* if the CPU supports PRNG stckf is present too */
 119                 asm volatile(".insn     s,0xb27c0000,%0"
 120                              : "=m" (*((unsigned long long *)p->buf)) : : "cc");
 121
 122                 /*
 123                  * Beside the STCKF the input for the TDES-EDE is the output
 124                  * of the last operation. We differ here from X9.17 since we
 125                  * only store one timestamp into the buffer. Padding the whole
 126                  * buffer with timestamps does not improve security, since
 127                  * successive stckf have nearly constant offsets.
 128                  * If an attacker knows the first timestamp it would be
 129                  * trivial to guess the additional values. One timestamp
 130                  * is therefore enough and still guarantees unique input values.
 131                  *
 132                  * Note: you can still get strict X9.17 conformity by setting
 133                  * prng_chunk_size to 8 bytes.
 134                 */
 135                 tmp = crypt_s390_kmc(KMC_PRNG, parm_block, p->buf, p->buf, n);
 136                 BUG_ON((tmp < 0) || (tmp != n));
 137
 138                 p->count += n;
 139
 140                 if (copy_to_user(ubuf, p->buf, chunk))
 141                         return -EFAULT;
 142
 143                 nbytes -= chunk;
 144                 ret += chunk;
 145                 ubuf += chunk;
 146         }
 147         return ret;
 148 }
 149
 150 static const struct file_operations prng_fops = {
 151         .owner          = THIS_MODULE,
 152         .open           = &prng_open,
 153         .release        = NULL,
 154         .read           = &prng_read,
 155         .llseek         = noop_llseek,
 156 };
 157
 158 static struct miscdevice prng_dev = {
 159         .name   = "prandom",
 160         .minor  = MISC_DYNAMIC_MINOR,
 161         .fops   = &prng_fops,
 162 };
 163
 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, CRYPT_S390_MSA))
 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
 201 static void __exit prng_exit(void)
 202 {
 203         /* wipe me */
 204         kzfree(p->buf);
 205         kfree(p);
 206
 207         misc_deregister(&prng_dev);
 208 }
 209
 210 module_init(prng_init);
 211 module_exit(prng_exit);