/* * random.c -- A strong random number generator * * Copyright Matt Mackall , 2003, 2004, 2005 * * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. 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 General 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, ALL OF * WHICH ARE HEREBY 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 NOT ADVISED OF THE POSSIBILITY OF SUCH * DAMAGE. */ /* * (now, with legal B.S. out of the way.....) * * This routine gathers environmental noise from device drivers, etc., * and returns good random numbers, suitable for cryptographic use. * Besides the obvious cryptographic uses, these numbers are also good * for seeding TCP sequence numbers, and other places where it is * desirable to have numbers which are not only random, but hard to * predict by an attacker. * * Theory of operation * =================== * * Computers are very predictable devices. Hence it is extremely hard * to produce truly random numbers on a computer --- as opposed to * pseudo-random numbers, which can easily generated by using a * algorithm. Unfortunately, it is very easy for attackers to guess * the sequence of pseudo-random number generators, and for some * applications this is not acceptable. So instead, we must try to * gather "environmental noise" from the computer's environment, which * must be hard for outside attackers to observe, and use that to * generate random numbers. In a Unix environment, this is best done * from inside the kernel. * * Sources of randomness from the environment include inter-keyboard * timings, inter-interrupt timings from some interrupts, and other * events which are both (a) non-deterministic and (b) hard for an * outside observer to measure. Randomness from these sources are * added to an "entropy pool", which is mixed using a CRC-like function. * This is not cryptographically strong, but it is adequate assuming * the randomness is not chosen maliciously, and it is fast enough that * the overhead of doing it on every interrupt is very reasonable. * As random bytes are mixed into the entropy pool, the routines keep * an *estimate* of how many bits of randomness have been stored into * the random number generator's internal state. * * When random bytes are desired, they are obtained by taking the SHA * hash of the contents of the "entropy pool". The SHA hash avoids * exposing the internal state of the entropy pool. It is believed to * be computationally infeasible to derive any useful information * about the input of SHA from its output. Even if it is possible to * analyze SHA in some clever way, as long as the amount of data * returned from the generator is less than the inherent entropy in * the pool, the output data is totally unpredictable. For this * reason, the routine decreases its internal estimate of how many * bits of "true randomness" are contained in the entropy pool as it * outputs random numbers. * * If this estimate goes to zero, the routine can still generate * random numbers; however, an attacker may (at least in theory) be * able to infer the future output of the generator from prior * outputs. This requires successful cryptanalysis of SHA, which is * not believed to be feasible, but there is a remote possibility. * Nonetheless, these numbers should be useful for the vast majority * of purposes. * * Exported interfaces ---- output * =============================== * * There are three exported interfaces; the first is one designed to * be used from within the kernel: * * void get_random_bytes(void *buf, int nbytes); * * This interface will return the requested number of random bytes, * and place it in the requested buffer. * * The two other interfaces are two character devices /dev/random and * /dev/urandom. /dev/random is suitable for use when very high * quality randomness is desired (for example, for key generation or * one-time pads), as it will only return a maximum of the number of * bits of randomness (as estimated by the random number generator) * contained in the entropy pool. * * The /dev/urandom device does not have this limit, and will return * as many bytes as are requested. As more and more random bytes are * requested without giving time for the entropy pool to recharge, * this will result in random numbers that are merely cryptographically * strong. For many applications, however, this is acceptable. * * Exported interfaces ---- input * ============================== * * The current exported interfaces for gathering environmental noise * from the devices are: * * void add_device_randomness(const void *buf, unsigned int size); * void add_input_randomness(unsigned int type, unsigned int code, * unsigned int value); * void add_interrupt_randomness(int irq, int irq_flags); * void add_disk_randomness(struct gendisk *disk); * * add_device_randomness() is for adding data to the random pool that * is likely to differ between two devices (or possibly even per boot). * This would be things like MAC addresses or serial numbers, or the * read-out of the RTC. This does *not* add any actual entropy to the * pool, but it initializes the pool to different values for devices * that might otherwise be identical and have very little entropy * available to them (particularly common in the embedded world). * * add_input_randomness() uses the input layer interrupt timing, as well as * the event type information from the hardware. * * add_interrupt_randomness() uses the interrupt timing as random * inputs to the entropy pool. Using the cycle counters and the irq source * as inputs, it feeds the randomness roughly once a second. * * add_disk_randomness() uses what amounts to the seek time of block * layer request events, on a per-disk_devt basis, as input to the * entropy pool. Note that high-speed solid state drives with very low * seek times do not make for good sources of entropy, as their seek * times are usually fairly consistent. * * All of these routines try to estimate how many bits of randomness a * particular randomness source. They do this by keeping track of the * first and second order deltas of the event timings. * * Ensuring unpredictability at system startup * ============================================ * * When any operating system starts up, it will go through a sequence * of actions that are fairly predictable by an adversary, especially * if the start-up does not involve interaction with a human operator. * This reduces the actual number of bits of unpredictability in the * entropy pool below the value in entropy_count. In order to * counteract this effect, it helps to carry information in the * entropy pool across shut-downs and start-ups. To do this, put the * following lines an appropriate script which is run during the boot * sequence: * * echo "Initializing random number generator..." * random_seed=/var/run/random-seed * # Carry a random seed from start-up to start-up * # Load and then save the whole entropy pool * if [ -f $random_seed ]; then * cat $random_seed >/dev/urandom * else * touch $random_seed * fi * chmod 600 $random_seed * dd if=/dev/urandom of=$random_seed count=1 bs=512 * * and the following lines in an appropriate script which is run as * the system is shutdown: * * # Carry a random seed from shut-down to start-up * # Save the whole entropy pool * echo "Saving random seed..." * random_seed=/var/run/random-seed * touch $random_seed * chmod 600 $random_seed * dd if=/dev/urandom of=$random_seed count=1 bs=512 * * For example, on most modern systems using the System V init * scripts, such code fragments would be found in * /etc/rc.d/init.d/random. On older Linux systems, the correct script * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0. * * Effectively, these commands cause the contents of the entropy pool * to be saved at shut-down time and reloaded into the entropy pool at * start-up. (The 'dd' in the addition to the bootup script is to * make sure that /etc/random-seed is different for every start-up, * even if the system crashes without executing rc.0.) Even with * complete knowledge of the start-up activities, predicting the state * of the entropy pool requires knowledge of the previous history of * the system. * * Configuring the /dev/random driver under Linux * ============================================== * * The /dev/random driver under Linux uses minor numbers 8 and 9 of * the /dev/mem major number (#1). So if your system does not have * /dev/random and /dev/urandom created already, they can be created * by using the commands: * * mknod /dev/random c 1 8 * mknod /dev/urandom c 1 9 * * Acknowledgements: * ================= * * Ideas for constructing this random number generator were derived * from Pretty Good Privacy's random number generator, and from private * discussions with Phil Karn. Colin Plumb provided a faster random * number generator, which speed up the mixing function of the entropy * pool, taken from PGPfone. Dale Worley has also contributed many * useful ideas and suggestions to improve this driver. * * Any flaws in the design are solely my responsibility, and should * not be attributed to the Phil, Colin, or any of authors of PGP. * * Further background information on this topic may be obtained from * RFC 1750, "Randomness Recommendations for Security", by Donald * Eastlake, Steve Crocker, and Jeff Schiller. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define CREATE_TRACE_POINTS #include /* * Configuration information */ #define INPUT_POOL_SHIFT 12 #define INPUT_POOL_WORDS (1 << (INPUT_POOL_SHIFT-5)) #define OUTPUT_POOL_SHIFT 10 #define OUTPUT_POOL_WORDS (1 << (OUTPUT_POOL_SHIFT-5)) #define SEC_XFER_SIZE 512 #define EXTRACT_SIZE 10 #define DEBUG_RANDOM_BOOT 0 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long)) /* * To allow fractional bits to be tracked, the entropy_count field is * denominated in units of 1/8th bits. * * 2*(ENTROPY_SHIFT + log2(poolbits)) must <= 31, or the multiply in * credit_entropy_bits() needs to be 64 bits wide. */ #define ENTROPY_SHIFT 3 #define ENTROPY_BITS(r) ((r)->entropy_count >> ENTROPY_SHIFT) /* * The minimum number of bits of entropy before we wake up a read on * /dev/random. Should be enough to do a significant reseed. */ static int random_read_wakeup_thresh = 64; /* * If the entropy count falls under this number of bits, then we * should wake up processes which are selecting or polling on write * access to /dev/random. */ static int random_write_wakeup_thresh = 28 * OUTPUT_POOL_WORDS; /* * The minimum number of seconds between urandom pool reseeding. We * do this to limit the amount of entropy that can be drained from the * input pool even if there are heavy demands on /dev/urandom. */ static int random_min_urandom_seed = 60; /* * Originally, we used a primitive polynomial of degree .poolwords * over GF(2). The taps for various sizes are defined below. They * were chosen to be evenly spaced except for the last tap, which is 1 * to get the twisting happening as fast as possible. * * For the purposes of better mixing, we use the CRC-32 polynomial as * well to make a (modified) twisted Generalized Feedback Shift * Register. (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR * generators. ACM Transactions on Modeling and Computer Simulation * 2(3):179-194. Also see M. Matsumoto & Y. Kurita, 1994. Twisted * GFSR generators II. ACM Transactions on Modeling and Computer * Simulation 4:254-266) * * Thanks to Colin Plumb for suggesting this. * * The mixing operation is much less sensitive than the output hash, * where we use SHA-1. All that we want of mixing operation is that * it be a good non-cryptographic hash; i.e. it not produce collisions * when fed "random" data of the sort we expect to see. As long as * the pool state differs for different inputs, we have preserved the * input entropy and done a good job. The fact that an intelligent * attacker can construct inputs that will produce controlled * alterations to the pool's state is not important because we don't * consider such inputs to contribute any randomness. The only * property we need with respect to them is that the attacker can't * increase his/her knowledge of the pool's state. Since all * additions are reversible (knowing the final state and the input, * you can reconstruct the initial state), if an attacker has any * uncertainty about the initial state, he/she can only shuffle that * uncertainty about, but never cause any collisions (which would * decrease the uncertainty). * * Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and * Videau in their paper, "The Linux Pseudorandom Number Generator * Revisited" (see: http://eprint.iacr.org/2012/251.pdf). In their * paper, they point out that we are not using a true Twisted GFSR, * since Matsumoto & Kurita used a trinomial feedback polynomial (that * is, with only three taps, instead of the six that we are using). * As a result, the resulting polynomial is neither primitive nor * irreducible, and hence does not have a maximal period over * GF(2**32). They suggest a slight change to the generator * polynomial which improves the resulting TGFSR polynomial to be * irreducible, which we have made here. */ static struct poolinfo { int poolbitshift, poolwords, poolbytes, poolbits, poolfracbits; #define S(x) ilog2(x)+5, (x), (x)*4, (x)*32, (x) << (ENTROPY_SHIFT+5) int tap1, tap2, tap3, tap4, tap5; } poolinfo_table[] = { /* was: x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 */ /* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */ { S(128), 104, 76, 51, 25, 1 }, /* was: x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 */ /* x^32 + x^26 + x^19 + x^14 + x^7 + x + 1 */ { S(32), 26, 19, 14, 7, 1 }, #if 0 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */ { S(2048), 1638, 1231, 819, 411, 1 }, /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */ { S(1024), 817, 615, 412, 204, 1 }, /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */ { S(1024), 819, 616, 410, 207, 2 }, /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */ { S(512), 411, 308, 208, 104, 1 }, /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */ { S(512), 409, 307, 206, 102, 2 }, /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */ { S(512), 409, 309, 205, 103, 2 }, /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */ { S(256), 205, 155, 101, 52, 1 }, /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */ { S(128), 103, 78, 51, 27, 2 }, /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */ { S(64), 52, 39, 26, 14, 1 }, #endif }; /* * Static global variables */ static DECLARE_WAIT_QUEUE_HEAD(random_read_wait); static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); static struct fasync_struct *fasync; /********************************************************************** * * OS independent entropy store. Here are the functions which handle * storing entropy in an entropy pool. * **********************************************************************/ struct entropy_store; struct entropy_store { /* read-only data: */ const struct poolinfo *poolinfo; __u32 *pool; const char *name; struct entropy_store *pull; struct work_struct push_work; /* read-write data: */ unsigned long last_pulled; spinlock_t lock; unsigned short add_ptr; unsigned short input_rotate; int entropy_count; int entropy_total; unsigned int initialized:1; unsigned int limit:1; unsigned int last_data_init:1; __u8 last_data[EXTRACT_SIZE]; }; static void push_to_pool(struct work_struct *work); static __u32 input_pool_data[INPUT_POOL_WORDS]; static __u32 blocking_pool_data[OUTPUT_POOL_WORDS]; static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS]; static struct entropy_store input_pool = { .poolinfo = &poolinfo_table[0], .name = "input", .limit = 1, .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), .pool = input_pool_data }; static struct entropy_store blocking_pool = { .poolinfo = &poolinfo_table[1], .name = "blocking", .limit = 1, .pull = &input_pool, .lock = __SPIN_LOCK_UNLOCKED(blocking_pool.lock), .pool = blocking_pool_data, .push_work = __WORK_INITIALIZER(blocking_pool.push_work, push_to_pool), }; static struct entropy_store nonblocking_pool = { .poolinfo = &poolinfo_table[1], .name = "nonblocking", .pull = &input_pool, .lock = __SPIN_LOCK_UNLOCKED(nonblocking_pool.lock), .pool = nonblocking_pool_data, .push_work = __WORK_INITIALIZER(nonblocking_pool.push_work, push_to_pool), }; static __u32 const twist_table[8] = { 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158, 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 }; /* * This function adds bytes into the entropy "pool". It does not * update the entropy estimate. The caller should call * credit_entropy_bits if this is appropriate. * * The pool is stirred with a primitive polynomial of the appropriate * degree, and then twisted. We twist by three bits at a time because * it's cheap to do so and helps slightly in the expected case where * the entropy is concentrated in the low-order bits. */ static void _mix_pool_bytes(struct entropy_store *r, const void *in, int nbytes, __u8 out[64]) { unsigned long i, j, tap1, tap2, tap3, tap4, tap5; int input_rotate; int wordmask = r->poolinfo->poolwords - 1; const char *bytes = in; __u32 w; tap1 = r->poolinfo->tap1; tap2 = r->poolinfo->tap2; tap3 = r->poolinfo->tap3; tap4 = r->poolinfo->tap4; tap5 = r->poolinfo->tap5; smp_rmb(); input_rotate = ACCESS_ONCE(r->input_rotate); i = ACCESS_ONCE(r->add_ptr); /* mix one byte at a time to simplify size handling and churn faster */ while (nbytes--) { w = rol32(*bytes++, input_rotate); i = (i - 1) & wordmask; /* XOR in the various taps */ w ^= r->pool[i]; w ^= r->pool[(i + tap1) & wordmask]; w ^= r->pool[(i + tap2) & wordmask]; w ^= r->pool[(i + tap3) & wordmask]; w ^= r->pool[(i + tap4) & wordmask]; w ^= r->pool[(i + tap5) & wordmask]; /* Mix the result back in with a twist */ r->pool[i] = (w >> 3) ^ twist_table[w & 7]; /* * Normally, we add 7 bits of rotation to the pool. * At the beginning of the pool, add an extra 7 bits * rotation, so that successive passes spread the * input bits across the pool evenly. */ input_rotate = (input_rotate + (i ? 7 : 14)) & 31; } ACCESS_ONCE(r->input_rotate) = input_rotate; ACCESS_ONCE(r->add_ptr) = i; smp_wmb(); if (out) for (j = 0; j < 16; j++) ((__u32 *)out)[j] = r->pool[(i - j) & wordmask]; } static void __mix_pool_bytes(struct entropy_store *r, const void *in, int nbytes, __u8 out[64]) { trace_mix_pool_bytes_nolock(r->name, nbytes, _RET_IP_); _mix_pool_bytes(r, in, nbytes, out); } static void mix_pool_bytes(struct entropy_store *r, const void *in, int nbytes, __u8 out[64]) { unsigned long flags; trace_mix_pool_bytes(r->name, nbytes, _RET_IP_); spin_lock_irqsave(&r->lock, flags); _mix_pool_bytes(r, in, nbytes, out); spin_unlock_irqrestore(&r->lock, flags); } struct fast_pool { __u32 pool[4]; unsigned long last; unsigned short count; unsigned char rotate; unsigned char last_timer_intr; }; /* * This is a fast mixing routine used by the interrupt randomness * collector. It's hardcoded for an 128 bit pool and assumes that any * locks that might be needed are taken by the caller. */ static void fast_mix(struct fast_pool *f, __u32 input[4]) { __u32 w; unsigned input_rotate = f->rotate; w = rol32(input[0], input_rotate) ^ f->pool[0] ^ f->pool[3]; f->pool[0] = (w >> 3) ^ twist_table[w & 7]; input_rotate = (input_rotate + 14) & 31; w = rol32(input[1], input_rotate) ^ f->pool[1] ^ f->pool[0]; f->pool[1] = (w >> 3) ^ twist_table[w & 7]; input_rotate = (input_rotate + 7) & 31; w = rol32(input[2], input_rotate) ^ f->pool[2] ^ f->pool[1]; f->pool[2] = (w >> 3) ^ twist_table[w & 7]; input_rotate = (input_rotate + 7) & 31; w = rol32(input[3], input_rotate) ^ f->pool[3] ^ f->pool[2]; f->pool[3] = (w >> 3) ^ twist_table[w & 7]; input_rotate = (input_rotate + 7) & 31; f->rotate = input_rotate; f->count++; } /* * Credit (or debit) the entropy store with n bits of entropy. * Use credit_entropy_bits_safe() if the value comes from userspace * or otherwise should be checked for extreme values. */ static void credit_entropy_bits(struct entropy_store *r, int nbits) { int entropy_count, orig; const int pool_size = r->poolinfo->poolfracbits; int nfrac = nbits << ENTROPY_SHIFT; if (!nbits) return; retry: entropy_count = orig = ACCESS_ONCE(r->entropy_count); if (nfrac < 0) { /* Debit */ entropy_count += nfrac; } else { /* * Credit: we have to account for the possibility of * overwriting already present entropy. Even in the * ideal case of pure Shannon entropy, new contributions * approach the full value asymptotically: * * entropy <- entropy + (pool_size - entropy) * * (1 - exp(-add_entropy/pool_size)) * * For add_entropy <= pool_size/2 then * (1 - exp(-add_entropy/pool_size)) >= * (add_entropy/pool_size)*0.7869... * so we can approximate the exponential with * 3/4*add_entropy/pool_size and still be on the * safe side by adding at most pool_size/2 at a time. * * The use of pool_size-2 in the while statement is to * prevent rounding artifacts from making the loop * arbitrarily long; this limits the loop to log2(pool_size)*2 * turns no matter how large nbits is. */ int pnfrac = nfrac; const int s = r->poolinfo->poolbitshift + ENTROPY_SHIFT + 2; /* The +2 corresponds to the /4 in the denominator */ do { unsigned int anfrac = min(pnfrac, pool_size/2); unsigned int add = ((pool_size - entropy_count)*anfrac*3) >> s; entropy_count += add; pnfrac -= anfrac; } while (unlikely(entropy_count < pool_size-2 && pnfrac)); } if (entropy_count < 0) { pr_warn("random: negative entropy/overflow: pool %s count %d\n", r->name, entropy_count); WARN_ON(1); entropy_count = 0; } else if (entropy_count > pool_size) entropy_count = pool_size; if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) goto retry; r->entropy_total += nbits; if (!r->initialized && r->entropy_total > 128) { r->initialized = 1; r->entropy_total = 0; if (r == &nonblocking_pool) { prandom_reseed_late(); pr_notice("random: %s pool is initialized\n", r->name); } } trace_credit_entropy_bits(r->name, nbits, entropy_count >> ENTROPY_SHIFT, r->entropy_total, _RET_IP_); if (r == &input_pool) { int entropy_bytes = entropy_count >> ENTROPY_SHIFT; /* should we wake readers? */ if (entropy_bytes >= random_read_wakeup_thresh) { wake_up_interruptible(&random_read_wait); kill_fasync(&fasync, SIGIO, POLL_IN); } /* If the input pool is getting full, send some * entropy to the two output pools, flipping back and * forth between them, until the output pools are 75% * full. */ if (entropy_bytes > random_write_wakeup_thresh && r->initialized && r->entropy_total >= 2*random_read_wakeup_thresh) { static struct entropy_store *last = &blocking_pool; struct entropy_store *other = &blocking_pool; if (last == &blocking_pool) other = &nonblocking_pool; if (other->entropy_count <= 3 * other->poolinfo->poolfracbits / 4) last = other; if (last->entropy_count <= 3 * last->poolinfo->poolfracbits / 4) { schedule_work(&last->push_work); r->entropy_total = 0; } } } } static void credit_entropy_bits_safe(struct entropy_store *r, int nbits) { const int nbits_max = (int)(~0U >> (ENTROPY_SHIFT + 1)); /* Cap the value to avoid overflows */ nbits = min(nbits, nbits_max); nbits = max(nbits, -nbits_max); credit_entropy_bits(r, nbits); } /********************************************************************* * * Entropy input management * *********************************************************************/ /* There is one of these per entropy source */ struct timer_rand_state { cycles_t last_time; long last_delta, last_delta2; unsigned dont_count_entropy:1; }; #define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, }; /* * Add device- or boot-specific data to the input and nonblocking * pools to help initialize them to unique values. * * None of this adds any entropy, it is meant to avoid the * problem of the nonblocking pool having similar initial state * across largely identical devices. */ void add_device_randomness(const void *buf, unsigned int size) { unsigned long time = random_get_entropy() ^ jiffies; unsigned long flags; trace_add_device_randomness(size, _RET_IP_); spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(&input_pool, buf, size, NULL); _mix_pool_bytes(&input_pool, &time, sizeof(time), NULL); spin_unlock_irqrestore(&input_pool.lock, flags); spin_lock_irqsave(&nonblocking_pool.lock, flags); _mix_pool_bytes(&nonblocking_pool, buf, size, NULL); _mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL); spin_unlock_irqrestore(&nonblocking_pool.lock, flags); } EXPORT_SYMBOL(add_device_randomness); static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE; /* * 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 many 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. * */ static void add_timer_randomness(struct timer_rand_state *state, unsigned num) { struct entropy_store *r; struct { long jiffies; unsigned cycles; unsigned num; } sample; long delta, delta2, delta3; preempt_disable(); sample.jiffies = jiffies; sample.cycles = random_get_entropy(); sample.num = num; r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool; mix_pool_bytes(r, &sample, sizeof(sample), NULL); /* * Calculate number of bits of randomness we probably added. * We take into account the first, second and third-order deltas * in order to make our estimate. */ if (!state->dont_count_entropy) { delta = sample.jiffies - state->last_time; state->last_time = sample.jiffies; delta2 = delta - state->last_delta; state->last_delta = delta; delta3 = delta2 - state->last_delta2; state->last_delta2 = delta2; if (delta < 0) delta = -delta; if (delta2 < 0) delta2 = -delta2; if (delta3 < 0) delta3 = -delta3; if (delta > delta2) delta = delta2; if (delta > delta3) delta = delta3; /* * delta is now minimum absolute delta. * Round down by 1 bit on general principles, * and limit entropy entimate to 12 bits. */ credit_entropy_bits(r, min_t(int, fls(delta>>1), 11)); } preempt_enable(); } void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) { static unsigned char last_value; /* ignore autorepeat and the like */ if (value == last_value) return; last_value = value; add_timer_randomness(&input_timer_state, (type << 4) ^ code ^ (code >> 4) ^ value); trace_add_input_randomness(ENTROPY_BITS(&input_pool)); } EXPORT_SYMBOL_GPL(add_input_randomness); static DEFINE_PER_CPU(struct fast_pool, irq_randomness); void add_interrupt_randomness(int irq, int irq_flags) { struct entropy_store *r; struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness); struct pt_regs *regs = get_irq_regs(); unsigned long now = jiffies; cycles_t cycles = random_get_entropy(); __u32 input[4], c_high, j_high; __u64 ip; c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0; j_high = (sizeof(now) > 4) ? now >> 32 : 0; input[0] = cycles ^ j_high ^ irq; input[1] = now ^ c_high; ip = regs ? instruction_pointer(regs) : _RET_IP_; input[2] = ip; input[3] = ip >> 32; fast_mix(fast_pool, input); if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ)) return; fast_pool->last = now; r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool; __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL); /* * If we don't have a valid cycle counter, and we see * back-to-back timer interrupts, then skip giving credit for * any entropy. */ if (cycles == 0) { if (irq_flags & __IRQF_TIMER) { if (fast_pool->last_timer_intr) return; fast_pool->last_timer_intr = 1; } else fast_pool->last_timer_intr = 0; } credit_entropy_bits(r, 1); } #ifdef CONFIG_BLOCK void add_disk_randomness(struct gendisk *disk) { if (!disk || !disk->random) return; /* first major is 1, so we get >= 0x200 here */ add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); trace_add_disk_randomness(disk_devt(disk), ENTROPY_BITS(&input_pool)); } #endif /********************************************************************* * * Entropy extraction routines * *********************************************************************/ static ssize_t extract_entropy(struct entropy_store *r, void *buf, size_t nbytes, int min, int rsvd); /* * This utility inline function is responsible for transferring entropy * from the primary pool to the secondary extraction pool. We make * sure we pull enough for a 'catastrophic reseed'. */ static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes); static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes) { if (r->limit == 0 && random_min_urandom_seed) { unsigned long now = jiffies; if (time_before(now, r->last_pulled + random_min_urandom_seed * HZ)) return; r->last_pulled = now; } if (r->pull && r->entropy_count < (nbytes << (ENTROPY_SHIFT + 3)) && r->entropy_count < r->poolinfo->poolfracbits) _xfer_secondary_pool(r, nbytes); } static void _xfer_secondary_pool(struct entropy_store *r, size_t nbytes) { __u32 tmp[OUTPUT_POOL_WORDS]; /* For /dev/random's pool, always leave two wakeup worth's BITS */ int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4; int bytes = nbytes; /* pull at least as many as BYTES as wakeup BITS */ bytes = max_t(int, bytes, random_read_wakeup_thresh / 8); /* but never more than the buffer size */ bytes = min_t(int, bytes, sizeof(tmp)); trace_xfer_secondary_pool(r->name, bytes * 8, nbytes * 8, ENTROPY_BITS(r), ENTROPY_BITS(r->pull)); bytes = extract_entropy(r->pull, tmp, bytes, random_read_wakeup_thresh / 8, rsvd); mix_pool_bytes(r, tmp, bytes, NULL); credit_entropy_bits(r, bytes*8); } /* * Used as a workqueue function so that when the input pool is getting * full, we can "spill over" some entropy to the output pools. That * way the output pools can store some of the excess entropy instead * of letting it go to waste. */ static void push_to_pool(struct work_struct *work) { struct entropy_store *r = container_of(work, struct entropy_store, push_work); BUG_ON(!r); _xfer_secondary_pool(r, random_read_wakeup_thresh/8); trace_push_to_pool(r->name, r->entropy_count >> ENTROPY_SHIFT, r->pull->entropy_count >> ENTROPY_SHIFT); } /* * These functions extracts randomness from the "entropy pool", and * returns it in a buffer. * * The min parameter specifies the minimum amount we can pull before * failing to avoid races that defeat catastrophic reseeding while the * reserved parameter indicates how much entropy we must leave in the * pool after each pull to avoid starving other readers. * * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words. */ static size_t account(struct entropy_store *r, size_t nbytes, int min, int reserved) { unsigned long flags; int wakeup_write = 0; int have_bytes; int entropy_count, orig; size_t ibytes; /* Hold lock while accounting */ spin_lock_irqsave(&r->lock, flags); BUG_ON(r->entropy_count > r->poolinfo->poolfracbits); /* Can we pull enough? */ retry: entropy_count = orig = ACCESS_ONCE(r->entropy_count); have_bytes = entropy_count >> (ENTROPY_SHIFT + 3); ibytes = nbytes; if (have_bytes < min + reserved) { ibytes = 0; } else { /* If limited, never pull more than available */ if (r->limit && ibytes + reserved >= have_bytes) ibytes = have_bytes - reserved; if (have_bytes >= ibytes + reserved) entropy_count -= ibytes << (ENTROPY_SHIFT + 3); else entropy_count = reserved << (ENTROPY_SHIFT + 3); if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) goto retry; if ((r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_thresh) wakeup_write = 1; } spin_unlock_irqrestore(&r->lock, flags); trace_debit_entropy(r->name, 8 * ibytes); if (wakeup_write) { wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); } return ibytes; } static void extract_buf(struct entropy_store *r, __u8 *out) { int i; union { __u32 w[5]; unsigned long l[LONGS(20)]; } hash; __u32 workspace[SHA_WORKSPACE_WORDS]; __u8 extract[64]; unsigned long flags; /* Generate a hash across the pool, 16 words (512 bits) at a time */ sha_init(hash.w); spin_lock_irqsave(&r->lock, flags); for (i = 0; i < r->poolinfo->poolwords; i += 16) sha_transform(hash.w, (__u8 *)(r->pool + i), workspace); /* * If we have an architectural hardware random number * generator, mix that in, too. */ for (i = 0; i < LONGS(20); i++) { unsigned long v; if (!arch_get_random_long(&v)) break; hash.l[i] ^= v; } /* * We mix the hash back into the pool to prevent backtracking * attacks (where the attacker knows the state of the pool * plus the current outputs, and attempts to find previous * ouputs), unless the hash function can be inverted. By * mixing at least a SHA1 worth of hash data back, we make * brute-forcing the feedback as hard as brute-forcing the * hash. */ __mix_pool_bytes(r, hash.w, sizeof(hash.w), extract); spin_unlock_irqrestore(&r->lock, flags); /* * To avoid duplicates, we atomically extract a portion of the * pool while mixing, and hash one final time. */ sha_transform(hash.w, extract, workspace); memset(extract, 0, sizeof(extract)); memset(workspace, 0, sizeof(workspace)); /* * In case the hash function has some recognizable output * pattern, we fold it in half. Thus, we always feed back * twice as much data as we output. */ hash.w[0] ^= hash.w[3]; hash.w[1] ^= hash.w[4]; hash.w[2] ^= rol32(hash.w[2], 16); memcpy(out, &hash, EXTRACT_SIZE); memset(&hash, 0, sizeof(hash)); } static ssize_t extract_entropy(struct entropy_store *r, void *buf, size_t nbytes, int min, int reserved) { ssize_t ret = 0, i; __u8 tmp[EXTRACT_SIZE]; unsigned long flags; /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */ if (fips_enabled) { spin_lock_irqsave(&r->lock, flags); if (!r->last_data_init) { r->last_data_init = 1; spin_unlock_irqrestore(&r->lock, flags); trace_extract_entropy(r->name, EXTRACT_SIZE, ENTROPY_BITS(r), _RET_IP_); xfer_secondary_pool(r, EXTRACT_SIZE); extract_buf(r, tmp); spin_lock_irqsave(&r->lock, flags); memcpy(r->last_data, tmp, EXTRACT_SIZE); } spin_unlock_irqrestore(&r->lock, flags); } trace_extract_entropy(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_); xfer_secondary_pool(r, nbytes); nbytes = account(r, nbytes, min, reserved); while (nbytes) { extract_buf(r, tmp); if (fips_enabled) { spin_lock_irqsave(&r->lock, flags); if (!memcmp(tmp, r->last_data, EXTRACT_SIZE)) panic("Hardware RNG duplicated output!\n"); memcpy(r->last_data, tmp, EXTRACT_SIZE); spin_unlock_irqrestore(&r->lock, flags); } i = min_t(int, nbytes, EXTRACT_SIZE); memcpy(buf, tmp, i); nbytes -= i; buf += i; ret += i; } /* Wipe data just returned from memory */ memset(tmp, 0, sizeof(tmp)); return ret; } static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf, size_t nbytes) { ssize_t ret = 0, i; __u8 tmp[EXTRACT_SIZE]; trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_); xfer_secondary_pool(r, nbytes); nbytes = account(r, nbytes, 0, 0); while (nbytes) { if (need_resched()) { if (signal_pending(current)) { if (ret == 0) ret = -ERESTARTSYS; break; } schedule(); } extract_buf(r, tmp); i = min_t(int, nbytes, EXTRACT_SIZE); if (copy_to_user(buf, tmp, i)) { ret = -EFAULT; break; } nbytes -= i; buf += i; ret += i; } /* Wipe data just returned from memory */ memset(tmp, 0, sizeof(tmp)); return ret; } /* * This function is the exported kernel interface. It returns some * number of good random numbers, suitable for key generation, seeding * TCP sequence numbers, etc. It does not rely on the hardware random * number generator. For random bytes direct from the hardware RNG * (when available), use get_random_bytes_arch(). */ void get_random_bytes(void *buf, int nbytes) { #if DEBUG_RANDOM_BOOT > 0 if (unlikely(nonblocking_pool.initialized == 0)) printk(KERN_NOTICE "random: %pF get_random_bytes called " "with %d bits of entropy available\n", (void *) _RET_IP_, nonblocking_pool.entropy_total); #endif trace_get_random_bytes(nbytes, _RET_IP_); extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0); } EXPORT_SYMBOL(get_random_bytes); /* * This function will use the architecture-specific hardware random * number generator if it is available. The arch-specific hw RNG will * almost certainly be faster than what we can do in software, but it * is impossible to verify that it is implemented securely (as * opposed, to, say, the AES encryption of a sequence number using a * key known by the NSA). So it's useful if we need the speed, but * only if we're willing to trust the hardware manufacturer not to * have put in a back door. */ void get_random_bytes_arch(void *buf, int nbytes) { char *p = buf; trace_get_random_bytes_arch(nbytes, _RET_IP_); while (nbytes) { unsigned long v; int chunk = min(nbytes, (int)sizeof(unsigned long)); if (!arch_get_random_long(&v)) break; memcpy(p, &v, chunk); p += chunk; nbytes -= chunk; } if (nbytes) extract_entropy(&nonblocking_pool, p, nbytes, 0, 0); } EXPORT_SYMBOL(get_random_bytes_arch); /* * init_std_data - initialize pool with system data * * @r: pool to initialize * * This function clears the pool's entropy count and mixes some system * data into the pool to prepare it for use. The pool is not cleared * as that can only decrease the entropy in the pool. */ static void init_std_data(struct entropy_store *r) { int i; ktime_t now = ktime_get_real(); unsigned long rv; r->last_pulled = jiffies; mix_pool_bytes(r, &now, sizeof(now), NULL); for (i = r->poolinfo->poolbytes; i > 0; i -= sizeof(rv)) { if (!arch_get_random_long(&rv)) rv = random_get_entropy(); mix_pool_bytes(r, &rv, sizeof(rv), NULL); } mix_pool_bytes(r, utsname(), sizeof(*(utsname())), NULL); } /* * Note that setup_arch() may call add_device_randomness() * long before we get here. This allows seeding of the pools * with some platform dependent data very early in the boot * process. But it limits our options here. We must use * statically allocated structures that already have all * initializations complete at compile time. We should also * take care not to overwrite the precious per platform data * we were given. */ static int rand_initialize(void) { init_std_data(&input_pool); init_std_data(&blocking_pool); init_std_data(&nonblocking_pool); return 0; } early_initcall(rand_initialize); #ifdef CONFIG_BLOCK void rand_initialize_disk(struct gendisk *disk) { struct timer_rand_state *state; /* * If kzalloc returns null, we just won't use that entropy * source. */ state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL); if (state) { state->last_time = INITIAL_JIFFIES; disk->random = state; } } #endif static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { ssize_t n, retval = 0, count = 0; if (nbytes == 0) return 0; while (nbytes > 0) { n = nbytes; if (n > SEC_XFER_SIZE) n = SEC_XFER_SIZE; n = extract_entropy_user(&blocking_pool, buf, n); if (n < 0) { retval = n; break; } trace_random_read(n*8, (nbytes-n)*8, ENTROPY_BITS(&blocking_pool), ENTROPY_BITS(&input_pool)); if (n == 0) { if (file->f_flags & O_NONBLOCK) { retval = -EAGAIN; break; } wait_event_interruptible(random_read_wait, ENTROPY_BITS(&input_pool) >= random_read_wakeup_thresh); if (signal_pending(current)) { retval = -ERESTARTSYS; break; } continue; } count += n; buf += n; nbytes -= n; break; /* This break makes the device work */ /* like a named pipe */ } return (count ? count : retval); } static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { int ret; if (unlikely(nonblocking_pool.initialized == 0)) printk_once(KERN_NOTICE "random: %s urandom read " "with %d bits of entropy available\n", current->comm, nonblocking_pool.entropy_total); ret = extract_entropy_user(&nonblocking_pool, buf, nbytes); trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool), ENTROPY_BITS(&input_pool)); return ret; } static unsigned int random_poll(struct file *file, poll_table * wait) { unsigned int mask; poll_wait(file, &random_read_wait, wait); poll_wait(file, &random_write_wait, wait); mask = 0; if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_thresh) mask |= POLLIN | POLLRDNORM; if (ENTROPY_BITS(&input_pool) < random_write_wakeup_thresh) mask |= POLLOUT | POLLWRNORM; return mask; } static int write_pool(struct entropy_store *r, const char __user *buffer, size_t count) { size_t bytes; __u32 buf[16]; const char __user *p = buffer; while (count > 0) { bytes = min(count, sizeof(buf)); if (copy_from_user(&buf, p, bytes)) return -EFAULT; count -= bytes; p += bytes; mix_pool_bytes(r, buf, bytes, NULL); cond_resched(); } return 0; } static ssize_t random_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos) { size_t ret; ret = write_pool(&blocking_pool, buffer, count); if (ret) return ret; ret = write_pool(&nonblocking_pool, buffer, count); if (ret) return ret; return (ssize_t)count; } static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) { int size, ent_count; int __user *p = (int __user *)arg; int retval; switch (cmd) { case RNDGETENTCNT: /* inherently racy, no point locking */ ent_count = ENTROPY_BITS(&input_pool); if (put_user(ent_count, p)) return -EFAULT; return 0; case RNDADDTOENTCNT: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ent_count, p)) return -EFAULT; credit_entropy_bits_safe(&input_pool, ent_count); return 0; case RNDADDENTROPY: if (!capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ent_count, p++)) return -EFAULT; if (ent_count < 0) return -EINVAL; if (get_user(size, p++)) return -EFAULT; retval = write_pool(&input_pool, (const char __user *)p, size); if (retval < 0) return retval; credit_entropy_bits_safe(&input_pool, ent_count); return 0; case RNDZAPENTCNT: case RNDCLEARPOOL: /* * Clear the entropy pool counters. We no longer clear * the entropy pool, as that's silly. */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; input_pool.entropy_count = 0; nonblocking_pool.entropy_count = 0; blocking_pool.entropy_count = 0; return 0; default: return -EINVAL; } } static int random_fasync(int fd, struct file *filp, int on) { return fasync_helper(fd, filp, on, &fasync); } const struct file_operations random_fops = { .read = random_read, .write = random_write, .poll = random_poll, .unlocked_ioctl = random_ioctl, .fasync = random_fasync, .llseek = noop_llseek, }; const struct file_operations urandom_fops = { .read = urandom_read, .write = random_write, .unlocked_ioctl = random_ioctl, .fasync = random_fasync, .llseek = noop_llseek, }; /*************************************************************** * Random UUID interface * * Used here for a Boot ID, but can be useful for other kernel * drivers. ***************************************************************/ /* * Generate random UUID */ void generate_random_uuid(unsigned char uuid_out[16]) { get_random_bytes(uuid_out, 16); /* Set UUID version to 4 --- truly random generation */ uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40; /* Set the UUID variant to DCE */ uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80; } EXPORT_SYMBOL(generate_random_uuid); /******************************************************************** * * Sysctl interface * ********************************************************************/ #ifdef CONFIG_SYSCTL #include static int min_read_thresh = 8, min_write_thresh; static int max_read_thresh = INPUT_POOL_WORDS * 32; static int max_write_thresh = INPUT_POOL_WORDS * 32; static char sysctl_bootid[16]; /* * This function is used to return both the bootid UUID, and random * UUID. The difference is in whether table->data is NULL; if it is, * then a new UUID is generated and returned to the user. * * If the user accesses this via the proc interface, the UUID will be * returned as an ASCII string in the standard UUID format; if via the * sysctl system call, as 16 bytes of binary data. */ static int proc_do_uuid(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { struct ctl_table fake_table; unsigned char buf[64], tmp_uuid[16], *uuid; uuid = table->data; if (!uuid) { uuid = tmp_uuid; generate_random_uuid(uuid); } else { static DEFINE_SPINLOCK(bootid_spinlock); spin_lock(&bootid_spinlock); if (!uuid[8]) generate_random_uuid(uuid); spin_unlock(&bootid_spinlock); } sprintf(buf, "%pU", uuid); fake_table.data = buf; fake_table.maxlen = sizeof(buf); return proc_dostring(&fake_table, write, buffer, lenp, ppos); } /* * Return entropy available scaled to integral bits */ static int proc_do_entropy(ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { ctl_table fake_table; int entropy_count; entropy_count = *(int *)table->data >> ENTROPY_SHIFT; fake_table.data = &entropy_count; fake_table.maxlen = sizeof(entropy_count); return proc_dointvec(&fake_table, write, buffer, lenp, ppos); } static int sysctl_poolsize = INPUT_POOL_WORDS * 32; extern struct ctl_table random_table[]; struct ctl_table random_table[] = { { .procname = "poolsize", .data = &sysctl_poolsize, .maxlen = sizeof(int), .mode = 0444, .proc_handler = proc_dointvec, }, { .procname = "entropy_avail", .maxlen = sizeof(int), .mode = 0444, .proc_handler = proc_do_entropy, .data = &input_pool.entropy_count, }, { .procname = "read_wakeup_threshold", .data = &random_read_wakeup_thresh, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec_minmax, .extra1 = &min_read_thresh, .extra2 = &max_read_thresh, }, { .procname = "write_wakeup_threshold", .data = &random_write_wakeup_thresh, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec_minmax, .extra1 = &min_write_thresh, .extra2 = &max_write_thresh, }, { .procname = "urandom_min_reseed_secs", .data = &random_min_urandom_seed, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec, }, { .procname = "boot_id", .data = &sysctl_bootid, .maxlen = 16, .mode = 0444, .proc_handler = proc_do_uuid, }, { .procname = "uuid", .maxlen = 16, .mode = 0444, .proc_handler = proc_do_uuid, }, { } }; #endif /* CONFIG_SYSCTL */ static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned; int random_int_secret_init(void) { get_random_bytes(random_int_secret, sizeof(random_int_secret)); return 0; } /* * Get a random word for internal kernel use only. Similar to urandom but * with the goal of minimal entropy pool depletion. As a result, the random * value is not cryptographically secure but for several uses the cost of * depleting entropy is too high */ static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash); unsigned int get_random_int(void) { __u32 *hash; unsigned int ret; if (arch_get_random_int(&ret)) return ret; hash = get_cpu_var(get_random_int_hash); hash[0] += current->pid + jiffies + random_get_entropy(); md5_transform(hash, random_int_secret); ret = hash[0]; put_cpu_var(get_random_int_hash); return ret; } EXPORT_SYMBOL(get_random_int); /* * randomize_range() returns a start address such that * * [...... .....] * start end * * a with size "len" starting at the return value is inside in the * area defined by [start, end], but is otherwise randomized. */ unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len) { unsigned long range = end - len - start; if (end <= start + len) return 0; return PAGE_ALIGN(get_random_int() % range + start); }