FreeBSD/Linux Kernel Cross Reference
sys/dev/random/darn.c

     /*-
      * Copyright (c) 2018 Justin Hibbits
      * Copyright (c) 2013 The FreeBSD Foundation
      * Copyright (c) 2013 David E. O'Brien <obrien@NUXI.org>
      * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
      * All rights reserved.
      *
      * Portions of this software were developed by Konstantin Belousov
      * under sponsorship from the FreeBSD Foundation.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer
     *    in this position and unchanged.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     *
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/kernel.h>
    #include <sys/conf.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/module.h>
    #include <sys/random.h>
    #include <sys/systm.h>
    
    #include <machine/cpu.h>
    #include <machine/md_var.h>
    
    #include <dev/random/randomdev.h>
    
    /*
     * Power ISA 3.0 adds a "darn" instruction (Deliver A Random Number).  The RNG
     * backing this instruction conforms to NIST SP800-90B and SP800-90C at the
     * point of hardware design, and provides a minimum of 0.5 bits of entropy per
     * bit.
     */
    
    #define RETRY_COUNT     10
    
    static u_int random_darn_read(void *, u_int);
    
    static struct random_source random_darn = {
            .rs_ident = "PowerISA DARN random number generator",
            .rs_source = RANDOM_PURE_DARN,
            .rs_read = random_darn_read
    };
    
    static inline int
    darn_rng_store(u_long *buf)
    {
            u_long rndval;
            int retry;
    
            for (retry = RETRY_COUNT; retry > 0; --retry) {
                    /* "DARN %rN, 1" instruction */
                    /*
                     * Arguments for DARN: rN and "L", where "L" can be one of:
                     * 0 - 32-bit conditional random number
                     * 1 - Conditional random number (conditioned to remove bias)
                     * 2 - Raw random number         (unprocessed, may include bias)
                     * 3 - Reserved
                     */
                    __asm __volatile(".long 0x7c0105e6 | (%0 << 21)" :
                        "+r"(rndval));
                    if (rndval != ~0)
                            break;
            }
    
            *buf = rndval;
            return (retry);
    }
    
    /* It is required that buf length is a multiple of sizeof(u_long). */
    static u_int
    random_darn_read(void *buf, u_int c)
    {
            u_long *b, rndval;
            u_int count;
    
           KASSERT(c % sizeof(*b) == 0, ("partial read %d", c));
           b = buf;
           for (count = c; count > 0; count -= sizeof(*b)) {
                   if (darn_rng_store(&rndval) == 0)
                           break;
                   *b++ = rndval;
           }
           return (c - count);
   }
   
   static int
   darn_modevent(module_t mod, int type, void *unused)
   {
           int error = 0;
   
           switch (type) {
           case MOD_LOAD:
                   if (cpu_features2 & PPC_FEATURE2_DARN) {
                           random_source_register(&random_darn);
                           printf("random: fast provider: \"%s\"\n", random_darn.rs_ident);
                   }
                   break;
   
           case MOD_UNLOAD:
                   if (cpu_features2 & PPC_FEATURE2_DARN)
                           random_source_deregister(&random_darn);
                   break;
   
           case MOD_SHUTDOWN:
                   break;
   
           default:
                   error = EOPNOTSUPP;
                   break;
   
           }
   
           return (error);
   }
   
   static moduledata_t darn_mod = {
           "darn",
           darn_modevent,
           0
   };
   
   DECLARE_MODULE(darn, darn_mod, SI_SUB_RANDOM, SI_ORDER_FOURTH);
   MODULE_VERSION(darn, 1);
   MODULE_DEPEND(darn, random_harvestq, 1, 1, 1);

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