FreeBSD/Linux Kernel Cross Reference
sys/i386/isa/random_machdep.c

     /*
      * random_machdep.c -- A strong random number generator
      *
      * $FreeBSD$
      *
      * Version 0.95, last modified 18-Oct-95
      * 
      * Copyright Theodore Ts'o, 1994, 1995.  All rights reserved.
      *
     * 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, and the entire permission notice in its entirety,
     *    including the disclaimer of warranties.
     * 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.
     * 3. The name of the author may not be used to endorse or promote
     *    products derived from this software without specific prior
     *    written permission.
     * 
     * ALTERNATIVELY, this product may be distributed under the terms of
     * the GNU Public License, in which case the provisions of the GPL are
     * required INSTEAD OF the above restrictions.  (This clause is
     * necessary due to a potential bad interaction between the GPL and
     * the restrictions contained in a BSD-style copyright.)
     * 
     * THIS SOFTWARE IS PROVIDED ``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/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/select.h>
    #include <sys/poll.h>
    #include <sys/md5.h>
    
    #include <machine/random.h>
    
    #include <i386/isa/icu.h>
    #include <i386/isa/intr_machdep.h>
    
    #define MAX_BLKDEV 4
    
    /*
     * The pool is stirred with a primitive polynomial of degree 128
     * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
     * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
     */
    #define POOLWORDS 128    /* Power of 2 - note that this is 32-bit words */
    #define POOLBITS (POOLWORDS*32)
    
    #if POOLWORDS == 128
    #define TAP1    99     /* The polynomial taps */
    #define TAP2    59
    #define TAP3    31
    #define TAP4    9
    #define TAP5    7
    #elif POOLWORDS == 64
    #define TAP1    62      /* The polynomial taps */
    #define TAP2    38
    #define TAP3    10
    #define TAP4    6
    #define TAP5    1
    #else
    #error No primitive polynomial available for chosen POOLWORDS
    #endif
    
    #define WRITEBUFFER 512 /* size in bytes */
    
    /* There is actually only one of these, globally. */
    struct random_bucket {
            u_int   add_ptr;
            u_int   entropy_count;
            int     input_rotate;
            u_int32_t *pool;
            struct  selinfo rsel;
    };
    
    /* There is one of these per entropy source */
    struct timer_rand_state {
            u_long  last_time;
            int     last_delta;
            int     nbits;
    };
    
    static struct random_bucket random_state;
    static u_int32_t random_pool[POOLWORDS];
   static struct timer_rand_state keyboard_timer_state;
   static struct timer_rand_state extract_timer_state;
   static struct timer_rand_state irq_timer_state[ICU_LEN];
   #ifdef notyet
   static struct timer_rand_state blkdev_timer_state[MAX_BLKDEV];
   #endif
   static struct wait_queue *random_wait;
   
   #ifndef MIN
   #define MIN(a,b) (((a) < (b)) ? (a) : (b))
   #endif
           
   void
   rand_initialize(void)
   {
           random_state.add_ptr = 0;
           random_state.entropy_count = 0;
           random_state.pool = random_pool;
           random_wait = NULL;
           random_state.rsel.si_flags = 0;
           random_state.rsel.si_pid = 0;
   }
   
   /*
    * This function adds an int into the entropy "pool".  It does not
    * update the entropy estimate.  The caller must do this if appropriate.
    *
    * The pool is stirred with a primitive polynomial of degree 128
    * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
    * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
    * 
    * We rotate the input word by a changing number of bits, to help
    * assure that all bits in the entropy get toggled.  Otherwise, if we
    * consistently feed the entropy pool small numbers (like ticks and
    * scancodes, for example), the upper bits of the entropy pool don't
    * get affected. --- TYT, 10/11/95
    */
   static __inline void
   add_entropy_word(struct random_bucket *r, const u_int32_t input)
   {
           u_int i;
           u_int32_t w;
   
           w = (input << r->input_rotate) | (input >> (32 - r->input_rotate));
           i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1);
           if (i)
                   r->input_rotate = (r->input_rotate + 7) & 31;
           else
                   /*
                    * At the beginning of the pool, add an extra 7 bits
                    * rotation, so that successive passes spread the
                    * input bits across the pool evenly.
                    */
                   r->input_rotate = (r->input_rotate + 14) & 31;
   
           /* XOR in the various taps */
           w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
           w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
           w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
           w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
           w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
           w ^= r->pool[i];
           /* Rotate w left 1 bit (stolen from SHA) and store */
           r->pool[i] = (w << 1) | (w >> 31);
   }
   
   /*
    * This function adds entropy to the entropy "pool" by using timing
    * delays.  It uses the timer_rand_state structure to make an estimate
    * of how  any bits of entropy this call has added to the pool.
    *
    * The number "num" is also added to the pool - it should somehow describe
    * the type of event which just happened.  This is currently 0-255 for
    * keyboard scan codes, and 256 upwards for interrupts.
    * On the i386, this is assumed to be at most 16 bits, and the high bits
    * are used for a high-resolution timer.
    */
   static void
   add_timer_randomness(struct random_bucket *r, struct timer_rand_state *state,
           u_int num)
   {
           int             delta, delta2;
           u_int           nbits;
           u_int32_t       time;
   
           num ^= timecounter->tc_get_timecount(timecounter) << 16;
           r->entropy_count += 2;
                   
           time = ticks;
   
           add_entropy_word(r, (u_int32_t) num);
           add_entropy_word(r, time);
   
           /*
            * Calculate number of bits of randomness we probably
            * added.  We take into account the first and second order
            * deltas in order to make our estimate.
            */
           delta = time - state->last_time;
           state->last_time = time;
   
           delta2 = delta - state->last_delta;
           state->last_delta = delta;
   
           if (delta < 0) delta = -delta;
           if (delta2 < 0) delta2 = -delta2;
           delta = MIN(delta, delta2) >> 1;
           for (nbits = 0; delta; nbits++)
                   delta >>= 1;
   
           r->entropy_count += nbits;
           
           /* Prevent overflow */
           if (r->entropy_count > POOLBITS)
                   r->entropy_count = POOLBITS;
   
           if (r->entropy_count >= 8)
                   selwakeup(&random_state.rsel);
   }
   
   void
   add_keyboard_randomness(u_char scancode)
   {
           add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
   }
   
   void
   add_interrupt_randomness(void *vsc)
   {
           int intr;
           struct random_softc *sc = vsc;
   
           (sc->sc_handler)(sc->sc_arg);
           intr = sc->sc_intr;
           add_timer_randomness(&random_state, &irq_timer_state[intr], intr);
   }
   
   #ifdef notused
   void
   add_blkdev_randomness(int major)
   {
           if (major >= MAX_BLKDEV)
                   return;
   
           add_timer_randomness(&random_state, &blkdev_timer_state[major],
                                0x200+major);
   }
   #endif /* notused */
   
   #if POOLWORDS % 16
   #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
   #endif
   /*
    * This function extracts randomness from the "entropy pool", and
    * returns it in a buffer.  This function computes how many remaining
    * bits of entropy are left in the pool, but it does not restrict the
    * number of bytes that are actually obtained.
    */
   static __inline int
   extract_entropy(struct random_bucket *r, char *buf, int nbytes)
   {
           int ret, i;
           u_int32_t tmp[4];
           
           add_timer_randomness(r, &extract_timer_state, nbytes);
           
           /* Redundant, but just in case... */
           if (r->entropy_count > POOLBITS) 
                   r->entropy_count = POOLBITS;
           /* Why is this here?  Left in from Ted Ts'o.  Perhaps to limit time. */
           if (nbytes > 32768)
                   nbytes = 32768;
   
           ret = nbytes;
           if (r->entropy_count / 8 >= nbytes)
                   r->entropy_count -= nbytes*8;
           else
                   r->entropy_count = 0;
   
           while (nbytes) {
                   /* Hash the pool to get the output */
                   tmp[0] = 0x67452301;
                   tmp[1] = 0xefcdab89;
                   tmp[2] = 0x98badcfe;
                   tmp[3] = 0x10325476;
                   for (i = 0; i < POOLWORDS; i += 16)
                           MD5Transform(tmp, (char *)(r->pool+i));
                   /* Modify pool so next hash will produce different results */
                   add_entropy_word(r, tmp[0]);
                   add_entropy_word(r, tmp[1]);
                   add_entropy_word(r, tmp[2]);
                   add_entropy_word(r, tmp[3]);
                   /*
                    * Run the MD5 Transform one more time, since we want
                    * to add at least minimal obscuring of the inputs to
                    * add_entropy_word().  --- TYT
                    */
                   MD5Transform(tmp, (char *)(r->pool));
                   
                   /* Copy data to destination buffer */
                   i = MIN(nbytes, 16);
                   bcopy(tmp, buf, i);
                   nbytes -= i;
                   buf += i;
           }
   
           /* Wipe data from memory */
           bzero(tmp, sizeof(tmp));
           
           return ret;
   }
   
   #ifdef notused /* XXX NOT the exported kernel interface */
   /*
    * This function is the exported kernel interface.  It returns some
    * number of good random numbers, suitable for seeding TCP sequence
    * numbers, etc.
    */
   void
   get_random_bytes(void *buf, u_int nbytes)
   {
           extract_entropy(&random_state, (char *) buf, nbytes);
   }
   #endif /* notused */
   
   u_int
   read_random(void *buf, u_int nbytes)
   {
           if ((nbytes * 8) > random_state.entropy_count)
                   nbytes = random_state.entropy_count / 8;
           
           return extract_entropy(&random_state, (char *)buf, nbytes);
   }
   
   u_int
   read_random_unlimited(void *buf, u_int nbytes)
   {
           return extract_entropy(&random_state, (char *)buf, nbytes);
   }
   
   #ifdef notused
   u_int
   write_random(const char *buf, u_int nbytes)
   {
           u_int i;
           u_int32_t word, *p;
   
           for (i = nbytes, p = (u_int32_t *)buf;
                i >= sizeof(u_int32_t);
                i-= sizeof(u_int32_t), p++)
                   add_entropy_word(&random_state, *p);
           if (i) {
                   word = 0;
                   bcopy(p, &word, i);
                   add_entropy_word(&random_state, word);
           }
           return nbytes;
   }
   #endif /* notused */
   
   int
   random_poll(dev_t dev, int events, struct proc *p)
   {
           int s;
           int revents = 0;
   
           s = splhigh();
           if (events & (POLLIN | POLLRDNORM))
                   if (random_state.entropy_count >= 8)
                           revents |= events & (POLLIN | POLLRDNORM);
                   else
                           selrecord(p, &random_state.rsel);
   
           splx(s);
           if (events & (POLLOUT | POLLWRNORM))
                   revents |= events & (POLLOUT | POLLWRNORM);     /* heh */
   
           return (revents);
   }
   

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