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/*
* Copyright IBM Corp. 2006,2007
* Author(s): Jan Glauber <jan.glauber@de.ibm.com>
* Driver for the s390 pseudo random number generator
*/
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/random.h>
#include <linux/slab.h>
#include <asm/debug.h>
#include <asm/uaccess.h>
#include "crypt_s390.h"
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Jan Glauber <jan.glauber@de.ibm.com>");
MODULE_DESCRIPTION("s390 PRNG interface");
static int prng_chunk_size = 256;
module_param(prng_chunk_size, int, S_IRUSR | S_IRGRP | S_IROTH);
MODULE_PARM_DESC(prng_chunk_size, "PRNG read chunk size in bytes");
static int prng_entropy_limit = 4096;
module_param(prng_entropy_limit, int, S_IRUSR | S_IRGRP | S_IROTH | S_IWUSR);
MODULE_PARM_DESC(prng_entropy_limit,
"PRNG add entropy after that much bytes were produced");
/*
* Any one who considers arithmetical methods of producing random digits is,
* of course, in a state of sin. -- John von Neumann
*/
struct s390_prng_data {
unsigned long count; /* how many bytes were produced */
char *buf;
};
static struct s390_prng_data *p;
/* copied from libica, use a non-zero initial parameter block */
static unsigned char parm_block[32] = {
0x0F,0x2B,0x8E,0x63,0x8C,0x8E,0xD2,0x52,0x64,0xB7,0xA0,0x7B,0x75,0x28,0xB8,0xF4,
0x75,0x5F,0xD2,0xA6,0x8D,0x97,0x11,0xFF,0x49,0xD8,0x23,0xF3,0x7E,0x21,0xEC,0xA0,
};
static int prng_open(struct inode *inode, struct file *file)
{
return nonseekable_open(inode, file);
}
static void prng_add_entropy(void)
{
__u64 entropy[4];
unsigned int i;
int ret;
for (i = 0; i < 16; i++) {
ret = crypt_s390_kmc(KMC_PRNG, parm_block, (char *)entropy,
(char *)entropy, sizeof(entropy));
BUG_ON(ret < 0 || ret != sizeof(entropy));
memcpy(parm_block, entropy, sizeof(entropy));
}
}
static void prng_seed(int nbytes)
{
char buf[16];
int i = 0;
BUG_ON(nbytes > 16);
get_random_bytes(buf, nbytes);
/* Add the entropy */
while (nbytes >= 8) {
*((__u64 *)parm_block) ^= *((__u64 *)buf+i);
prng_add_entropy();
i += 8;
nbytes -= 8;
}
prng_add_entropy();
}
static ssize_t prng_read(struct file *file, char __user *ubuf, size_t nbytes,
loff_t *ppos)
{
int chunk, n;
int ret = 0;
int tmp;
/* nbytes can be arbitrary length, we split it into chunks */
while (nbytes) {
/* same as in extract_entropy_user in random.c */
if (need_resched()) {
if (signal_pending(current)) {
if (ret == 0)
ret = -ERESTARTSYS;
break;
}
schedule();
}
/*
* we lose some random bytes if an attacker issues
* reads < 8 bytes, but we don't care
*/
chunk = min_t(int, nbytes, prng_chunk_size);
/* PRNG only likes multiples of 8 bytes */
n = (chunk + 7) & -8;
if (p->count > prng_entropy_limit)
prng_seed(8);
/* if the CPU supports PRNG stckf is present too */
asm volatile(".insn s,0xb27c0000,%0"
: "=m" (*((unsigned long long *)p->buf)) : : "cc");
/*
* Beside the STCKF the input for the TDES-EDE is the output
* of the last operation. We differ here from X9.17 since we
* only store one timestamp into the buffer. Padding the whole
* buffer with timestamps does not improve security, since
* successive stckf have nearly constant offsets.
* If an attacker knows the first timestamp it would be
* trivial to guess the additional values. One timestamp
* is therefore enough and still guarantees unique input values.
*
* Note: you can still get strict X9.17 conformity by setting
* prng_chunk_size to 8 bytes.
*/
tmp = crypt_s390_kmc(KMC_PRNG, parm_block, p->buf, p->buf, n);
BUG_ON((tmp < 0) || (tmp != n));
p->count += n;
if (copy_to_user(ubuf, p->buf, chunk))
return -EFAULT;
nbytes -= chunk;
ret += chunk;
ubuf += chunk;
}
return ret;
}
static const struct file_operations prng_fops = {
.owner = THIS_MODULE,
.open = &prng_open,
.release = NULL,
.read = &prng_read,
.llseek = noop_llseek,
};
static struct miscdevice prng_dev = {
.name = "prandom",
.minor = MISC_DYNAMIC_MINOR,
.fops = &prng_fops,
};
static int __init prng_init(void)
{
int ret;
/* check if the CPU has a PRNG */
if (!crypt_s390_func_available(KMC_PRNG))
return -EOPNOTSUPP;
if (prng_chunk_size < 8)
return -EINVAL;
p = kmalloc(sizeof(struct s390_prng_data), GFP_KERNEL);
if (!p)
return -ENOMEM;
p->count = 0;
p->buf = kmalloc(prng_chunk_size, GFP_KERNEL);
if (!p->buf) {
ret = -ENOMEM;
goto out_free;
}
/* initialize the PRNG, add 128 bits of entropy */
prng_seed(16);
ret = misc_register(&prng_dev);
if (ret)
goto out_buf;
return 0;
out_buf:
kfree(p->buf);
out_free:
kfree(p);
return ret;
}
static void __exit prng_exit(void)
{
/* wipe me */
kzfree(p->buf);
kfree(p);
misc_deregister(&prng_dev);
}
module_init(prng_init);
module_exit(prng_exit);
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