/*
 * 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/smp_lock.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/random.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)
{
        cycle_kernel_lock();
        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*8);
                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,
};

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);