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6265e169cd
linux/drivers/char/random.c
Theodore Ts'o 6265e169cd random: push extra entropy to the output pools 
As the input pool gets filled, start transfering entropy to the output
pools until they get filled.  This allows us to use the output pools
to store more system entropy.  Waste not, want not....

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:22 -04:00

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/*
* random.c -- A strong random number generator
*
* Copyright Matt Mackall <mpm@selenic.com>, 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 <linux/utsname.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/string.h>
#include <linux/fcntl.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/genhd.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/cryptohash.h>
#include <linux/fips.h>
#include <linux/ptrace.h>
#include <linux/kmemcheck.h>
#include <linux/workqueue.h>
#ifdef CONFIG_GENERIC_HARDIRQS
# include <linux/irq.h>
#endif
#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/io.h>
#define CREATE_TRACE_POINTS
#include <trace/events/random.h>
/*
* 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 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 resending. 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 Mdeling 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;
static bool debug;
module_param(debug, bool, 0644);
#define DEBUG_ENT(fmt, arg...) do { \
if (debug) \
printk(KERN_DEBUG "random %04d %04d %04d: " \
fmt,\
input_pool.entropy_count,\
blocking_pool.entropy_count,\
nonblocking_pool.entropy_count,\
## arg); } while (0)
/**********************************************************************
*
* 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;
DEBUG_ENT("added %d entropy credits to %s\n", nbits, r->name);
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) {
DEBUG_ENT("negative entropy/overflow\n");
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 && nbits > 0) {
if (r->entropy_total > 128) {
r->initialized = 1;
r->entropy_total = 0;
}
}
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;
};
/*
* 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;
/*
* 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 {
long jiffies;
unsigned cycles;
unsigned num;
} sample;
long delta, delta2, delta3;
preempt_disable();
sample.jiffies = jiffies;
sample.cycles = random_get_entropy();
sample.num = num;
mix_pool_bytes(&input_pool, &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(&input_pool,
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;
DEBUG_ENT("input event\n");
last_value = value;
add_timer_randomness(&input_timer_state,
(type << 4) ^ code ^ (code >> 4) ^ value);
}
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 */
DEBUG_ENT("disk event %d:%d\n",
MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
}
#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));
DEBUG_ENT("going to reseed %s with %d bits (%zu of %d requested)\n",
r->name, bytes * 8, nbytes * 8,
r->entropy_count >> ENTROPY_SHIFT);
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);
DEBUG_ENT("trying to extract %zu bits from %s\n",
nbytes * 8, r->name);
/* 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;
}
DEBUG_ENT("debiting %zu entropy credits from %s%s\n",
ibytes * 8, r->name, r->limit ? "" : " (unlimited)");
spin_unlock_irqrestore(&r->lock, flags);
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 a 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 use the hw random number
* generator, if available; use get_random_bytes_arch() for that.
*/
void get_random_bytes(void *buf, int nbytes)
{
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->entropy_count = 0;
r->entropy_total = 0;
r->last_data_init = 0;
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))
break;
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;
}
module_init(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)
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;
DEBUG_ENT("reading %zu bits\n", n*8);
n = extract_entropy_user(&blocking_pool, buf, n);
if (n < 0) {
retval = n;
break;
}
DEBUG_ENT("read got %zd bits (%zd still needed)\n",
n*8, (nbytes-n)*8);
if (n == 0) {
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
break;
}
DEBUG_ENT("sleeping?\n");
wait_event_interruptible(random_read_wait,
ENTROPY_BITS(&input_pool) >=
random_read_wakeup_thresh);
DEBUG_ENT("awake\n");
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)
{
return extract_entropy_user(&nonblocking_pool, buf, nbytes);
}
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. */
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
rand_initialize();
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 <linux/sysctl.h>
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];
/*
* These functions 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, it will be returned
* as an ASCII string in the standard UUID format. If accesses via the
* sysctl system call, it is returned 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
*
* [...... <range> .....]
* start end
*
* a <range> 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);
}
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