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

     /*-
      * 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/sysctl.h>
    #include <sys/systm.h>
    
    #include <machine/md_var.h>
    #include <machine/specialreg.h>
    #include <x86/ifunc.h>
    
    #include <dev/random/randomdev.h>
    
    #define RETRY_COUNT     10
    
    static bool has_rdrand, has_rdseed;
    static u_int random_ivy_read(void *, u_int);
    
    static struct random_source random_ivy = {
            .rs_ident = "Intel Secure Key RNG",
            .rs_source = RANDOM_PURE_RDRAND,
            .rs_read = random_ivy_read
    };
    
    SYSCTL_NODE(_kern_random, OID_AUTO, rdrand, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
        "rdrand (ivy) entropy source");
    static bool acquire_independent_seed_samples = false;
    SYSCTL_BOOL(_kern_random_rdrand, OID_AUTO, rdrand_independent_seed,
        CTLFLAG_RWTUN, &acquire_independent_seed_samples, 0,
        "If non-zero, use more expensive and slow, but safer, seeded samples "
        "where RDSEED is not present.");
    
    static bool
    x86_rdrand_store(u_long *buf)
    {
            u_long rndval, seed_iterations, i;
            int retry;
    
            /* Per [1], "§ 5.2.6 Generating Seeds from RDRAND,"
             * machines lacking RDSEED will guarantee RDRAND is reseeded every 8kB
             * of generated output.
             *
             * [1]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide#inpage-nav-6-8
             */
            if (acquire_independent_seed_samples)
                    seed_iterations = 8 * 1024 / sizeof(*buf);
            else
                    seed_iterations = 1;
    
            for (i = 0; i < seed_iterations; i++) {
                    retry = RETRY_COUNT;
                    __asm __volatile(
                        "1:\n\t"
                        "rdrand     %1\n\t" /* read randomness into rndval */
                        "jc         2f\n\t" /* CF is set on success, exit retry loop */
                        "dec        %0\n\t" /* otherwise, retry-- */
                        "jne        1b\n\t" /* and loop if retries are not exhausted */
                        "2:"
                        : "+r" (retry), "=r" (rndval) : : "cc");
                    if (retry == 0)
                            return (false);
           }
           *buf = rndval;
           return (true);
   }
   
   static bool
   x86_rdseed_store(u_long *buf)
   {
           u_long rndval;
           int retry;
   
           retry = RETRY_COUNT;
           __asm __volatile(
               "1:\n\t"
               "rdseed     %1\n\t" /* read randomness into rndval */
               "jc         2f\n\t" /* CF is set on success, exit retry loop */
               "dec        %0\n\t" /* otherwise, retry-- */
               "jne        1b\n\t" /* and loop if retries are not exhausted */
               "2:"
               : "+r" (retry), "=r" (rndval) : : "cc");
           *buf = rndval;
           return (retry != 0);
   }
   
   static bool
   x86_unimpl_store(u_long *buf __unused)
   {
   
           panic("%s called", __func__);
   }
   
   DEFINE_IFUNC(static, bool, x86_rng_store, (u_long *buf))
   {
           has_rdrand = (cpu_feature2 & CPUID2_RDRAND);
           has_rdseed = (cpu_stdext_feature & CPUID_STDEXT_RDSEED);
   
           if (has_rdseed)
                   return (x86_rdseed_store);
           else if (has_rdrand)
                   return (x86_rdrand_store);
           else
                   return (x86_unimpl_store);
   }
   
   /* It is required that buf length is a multiple of sizeof(u_long). */
   static u_int
   random_ivy_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 (!x86_rng_store(&rndval))
                           break;
                   *b++ = rndval;
           }
           return (c - count);
   }
   
   static int
   rdrand_modevent(module_t mod, int type, void *unused)
   {
           int error = 0;
   
           switch (type) {
           case MOD_LOAD:
                   if (has_rdrand || has_rdseed) {
                           random_source_register(&random_ivy);
                           printf("random: fast provider: \"%s\"\n", random_ivy.rs_ident);
                   }
                   break;
   
           case MOD_UNLOAD:
                   if (has_rdrand || has_rdseed)
                           random_source_deregister(&random_ivy);
                   break;
   
           case MOD_SHUTDOWN:
                   break;
   
           default:
                   error = EOPNOTSUPP;
                   break;
   
           }
   
           return (error);
   }
   
   static moduledata_t rdrand_mod = {
           "rdrand",
           rdrand_modevent,
           0
   };
   
   DECLARE_MODULE(rdrand, rdrand_mod, SI_SUB_RANDOM, SI_ORDER_FOURTH);
   MODULE_VERSION(rdrand, 1);
   MODULE_DEPEND(rdrand, random_harvestq, 1, 1, 1);

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