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OpenCloudOS-Kernel/drivers/char/random.c

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/*
* random.c -- A strong random number generator
*
* Copyright (C) 2017-2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*
* 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 BLAKE2s
* hash of the contents of the "entropy pool". The BLAKE2s 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 BLAKE2s from its output. Even if it is possible to
* analyze BLAKE2s 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 BLAKE2s, 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 four exported interfaces; two for use within the kernel,
* and two for use from userspace.
*
* Exported interfaces ---- userspace output
* -----------------------------------------
*
* The userspace 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 ---- kernel output
* --------------------------------------
*
* The primary kernel interface is
*
* 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. This is equivalent to a
* read from /dev/urandom.
*
* For less critical applications, there are the functions:
*
* u32 get_random_u32()
* u64 get_random_u64()
* unsigned int get_random_int()
* unsigned long get_random_long()
*
* These are produced by a cryptographic RNG seeded from get_random_bytes,
* and so do not deplete the entropy pool as much. These are recommended
* for most in-kernel operations *if the result is going to be stored in
* the kernel*.
*
* Specifically, the get_random_int() family do not attempt to do
* "anti-backtracking". If you capture the state of the kernel (e.g.
* by snapshotting the VM), you can figure out previous get_random_int()
* return values. But if the value is stored in the kernel anyway,
* this is not a problem.
*
* It *is* safe to expose get_random_int() output to attackers (e.g. as
* network cookies); given outputs 1..n, it's not feasible to predict
* outputs 0 or n+1. The only concern is an attacker who breaks into
* the kernel later; the get_random_int() engine is not reseeded as
* often as the get_random_bytes() one.
*
* get_random_bytes() is needed for keys that need to stay secret after
* they are erased from the kernel. For example, any key that will
* be wrapped and stored encrypted. And session encryption keys: we'd
* like to know that after the session is closed and the keys erased,
* the plaintext is unrecoverable to someone who recorded the ciphertext.
*
* But for network ports/cookies, stack canaries, PRNG seeds, address
* space layout randomization, session *authentication* keys, or other
* applications where the sensitive data is stored in the kernel in
* plaintext for as long as it's sensitive, the get_random_int() family
* is just fine.
*
* Consider ASLR. We want to keep the address space secret from an
* outside attacker while the process is running, but once the address
* space is torn down, it's of no use to an attacker any more. And it's
* stored in kernel data structures as long as it's alive, so worrying
* about an attacker's ability to extrapolate it from the get_random_int()
* CRNG is silly.
*
* Even some cryptographic keys are safe to generate with get_random_int().
* In particular, keys for SipHash are generally fine. Here, knowledge
* of the key authorizes you to do something to a kernel object (inject
* packets to a network connection, or flood a hash table), and the
* key is stored with the object being protected. Once it goes away,
* we no longer care if anyone knows the key.
*
* prandom_u32()
* -------------
*
* For even weaker applications, see the pseudorandom generator
* prandom_u32(), prandom_max(), and prandom_bytes(). If the random
* numbers aren't security-critical at all, these are *far* cheaper.
* Useful for self-tests, random error simulation, randomized backoffs,
* and any other application where you trust that nobody is trying to
* maliciously mess with you by guessing the "random" numbers.
*
* 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);
* void add_disk_randomness(struct gendisk *disk);
* void add_hwgenerator_randomness(const char *buffer, size_t count,
* size_t entropy);
* void add_bootloader_randomness(const void *buf, unsigned int size);
*
* 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.
*
* add_hwgenerator_randomness() is for true hardware RNGs, and will credit
* entropy as specified by the caller. If the entropy pool is full it will
* block until more entropy is needed.
*
* add_bootloader_randomness() is the same as add_hwgenerator_randomness() or
* add_device_randomness(), depending on whether or not the configuration
* option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
*
* 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.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#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/blkdev.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/nodemask.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/workqueue.h>
#include <linux/irq.h>
#include <linux/ratelimit.h>
#include <linux/syscalls.h>
#include <linux/completion.h>
#include <linux/uuid.h>
#include <crypto/chacha.h>
#include <crypto/blake2s.h>
#include <asm/processor.h>
#include <linux/uaccess.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/io.h>
#define CREATE_TRACE_POINTS
#include <trace/events/random.h>
/* #define ADD_INTERRUPT_BENCH */
/*
* 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_bits = 28 * (1 << 5);
/*
* 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 BLAKE2s. 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.
*/
enum poolinfo {
POOL_WORDS = 128,
POOL_WORDMASK = POOL_WORDS - 1,
POOL_BYTES = POOL_WORDS * sizeof(u32),
POOL_BITS = POOL_BYTES * 8,
POOL_BITSHIFT = ilog2(POOL_BITS),
/* To allow fractional bits to be tracked, the entropy_count field is
* denominated in units of 1/8th bits. */
POOL_ENTROPY_SHIFT = 3,
#define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT)
POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT,
/* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
POOL_TAP1 = 104,
POOL_TAP2 = 76,
POOL_TAP3 = 51,
POOL_TAP4 = 25,
POOL_TAP5 = 1,
EXTRACT_SIZE = BLAKE2S_HASH_SIZE / 2
};
/*
* Static global variables
*/
static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
static struct fasync_struct *fasync;
static DEFINE_SPINLOCK(random_ready_list_lock);
static LIST_HEAD(random_ready_list);
struct crng_state {
u32 state[16];
unsigned long init_time;
spinlock_t lock;
};
static struct crng_state primary_crng = {
.lock = __SPIN_LOCK_UNLOCKED(primary_crng.lock),
.state[0] = CHACHA_CONSTANT_EXPA,
.state[1] = CHACHA_CONSTANT_ND_3,
.state[2] = CHACHA_CONSTANT_2_BY,
.state[3] = CHACHA_CONSTANT_TE_K,
};
/*
* crng_init = 0 --> Uninitialized
* 1 --> Initialized
* 2 --> Initialized from input_pool
*
* crng_init is protected by primary_crng->lock, and only increases
* its value (from 0->1->2).
*/
static int crng_init = 0;
static bool crng_need_final_init = false;
#define crng_ready() (likely(crng_init > 1))
static int crng_init_cnt = 0;
static unsigned long crng_global_init_time = 0;
#define CRNG_INIT_CNT_THRESH (2 * CHACHA_KEY_SIZE)
static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE]);
static void _crng_backtrack_protect(struct crng_state *crng,
u8 tmp[CHACHA_BLOCK_SIZE], int used);
static void process_random_ready_list(void);
static void _get_random_bytes(void *buf, int nbytes);
static struct ratelimit_state unseeded_warning =
RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3);
static struct ratelimit_state urandom_warning =
RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
static int ratelimit_disable __read_mostly;
module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
/**********************************************************************
*
* OS independent entropy store. Here are the functions which handle
* storing entropy in an entropy pool.
*
**********************************************************************/
static u32 input_pool_data[POOL_WORDS] __latent_entropy;
static struct {
spinlock_t lock;
u16 add_ptr;
u16 input_rotate;
int entropy_count;
} input_pool = {
.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
};
static ssize_t extract_entropy(void *buf, size_t nbytes, int min);
static ssize_t _extract_entropy(void *buf, size_t nbytes);
static void crng_reseed(struct crng_state *crng, bool use_input_pool);
static const u32 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(const void *in, int nbytes)
{
unsigned long i;
int input_rotate;
const u8 *bytes = in;
u32 w;
input_rotate = input_pool.input_rotate;
i = input_pool.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) & POOL_WORDMASK;
/* XOR in the various taps */
w ^= input_pool_data[i];
w ^= input_pool_data[(i + POOL_TAP1) & POOL_WORDMASK];
w ^= input_pool_data[(i + POOL_TAP2) & POOL_WORDMASK];
w ^= input_pool_data[(i + POOL_TAP3) & POOL_WORDMASK];
w ^= input_pool_data[(i + POOL_TAP4) & POOL_WORDMASK];
w ^= input_pool_data[(i + POOL_TAP5) & POOL_WORDMASK];
/* Mix the result back in with a twist */
input_pool_data[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;
}
input_pool.input_rotate = input_rotate;
input_pool.add_ptr = i;
}
static void __mix_pool_bytes(const void *in, int nbytes)
{
trace_mix_pool_bytes_nolock(nbytes, _RET_IP_);
_mix_pool_bytes(in, nbytes);
}
static void mix_pool_bytes(const void *in, int nbytes)
{
unsigned long flags;
trace_mix_pool_bytes(nbytes, _RET_IP_);
spin_lock_irqsave(&input_pool.lock, flags);
_mix_pool_bytes(in, nbytes);
spin_unlock_irqrestore(&input_pool.lock, flags);
}
struct fast_pool {
u32 pool[4];
unsigned long last;
u16 reg_idx;
u8 count;
};
/*
* 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 a = f->pool[0], b = f->pool[1];
u32 c = f->pool[2], d = f->pool[3];
a += b; c += d;
b = rol32(b, 6); d = rol32(d, 27);
d ^= a; b ^= c;
a += b; c += d;
b = rol32(b, 16); d = rol32(d, 14);
d ^= a; b ^= c;
a += b; c += d;
b = rol32(b, 6); d = rol32(d, 27);
d ^= a; b ^= c;
a += b; c += d;
b = rol32(b, 16); d = rol32(d, 14);
d ^= a; b ^= c;
f->pool[0] = a; f->pool[1] = b;
f->pool[2] = c; f->pool[3] = d;
f->count++;
}
static void process_random_ready_list(void)
{
unsigned long flags;
struct random_ready_callback *rdy, *tmp;
spin_lock_irqsave(&random_ready_list_lock, flags);
list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
struct module *owner = rdy->owner;
list_del_init(&rdy->list);
rdy->func(rdy);
module_put(owner);
}
spin_unlock_irqrestore(&random_ready_list_lock, flags);
}
/*
* 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(int nbits)
{
int entropy_count, entropy_bits, orig;
int nfrac = nbits << POOL_ENTROPY_SHIFT;
/* Ensure that the multiplication can avoid being 64 bits wide. */
BUILD_BUG_ON(2 * (POOL_ENTROPY_SHIFT + POOL_BITSHIFT) > 31);
if (!nbits)
return;
retry:
entropy_count = orig = READ_ONCE(input_pool.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 = POOL_BITSHIFT + POOL_ENTROPY_SHIFT + 2;
/* The +2 corresponds to the /4 in the denominator */
do {
unsigned int anfrac = min(pnfrac, POOL_FRACBITS / 2);
unsigned int add =
((POOL_FRACBITS - entropy_count) * anfrac * 3) >> s;
entropy_count += add;
pnfrac -= anfrac;
} while (unlikely(entropy_count < POOL_FRACBITS - 2 && pnfrac));
}
if (WARN_ON(entropy_count < 0)) {
pr_warn("negative entropy/overflow: count %d\n", entropy_count);
entropy_count = 0;
} else if (entropy_count > POOL_FRACBITS)
entropy_count = POOL_FRACBITS;
if (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig)
goto retry;
trace_credit_entropy_bits(nbits, entropy_count >> POOL_ENTROPY_SHIFT, _RET_IP_);
entropy_bits = entropy_count >> POOL_ENTROPY_SHIFT;
if (crng_init < 2 && entropy_bits >= 128)
crng_reseed(&primary_crng, true);
}
static int credit_entropy_bits_safe(int nbits)
{
if (nbits < 0)
return -EINVAL;
/* Cap the value to avoid overflows */
nbits = min(nbits, POOL_BITS);
credit_entropy_bits(nbits);
return 0;
}
/*********************************************************************
*
* CRNG using CHACHA20
*
*********************************************************************/
#define CRNG_RESEED_INTERVAL (300 * HZ)
static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
/*
* Hack to deal with crazy userspace progams when they are all trying
* to access /dev/urandom in parallel. The programs are almost
* certainly doing something terribly wrong, but we'll work around
* their brain damage.
*/
static struct crng_state **crng_node_pool __read_mostly;
static void invalidate_batched_entropy(void);
static void numa_crng_init(void);
static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
static int __init parse_trust_cpu(char *arg)
{
return kstrtobool(arg, &trust_cpu);
}
early_param("random.trust_cpu", parse_trust_cpu);
static bool crng_init_try_arch(struct crng_state *crng)
{
int i;
bool arch_init = true;
unsigned long rv;
for (i = 4; i < 16; i++) {
if (!arch_get_random_seed_long(&rv) &&
!arch_get_random_long(&rv)) {
rv = random_get_entropy();
arch_init = false;
}
crng->state[i] ^= rv;
}
return arch_init;
}
static bool __init crng_init_try_arch_early(struct crng_state *crng)
{
int i;
bool arch_init = true;
unsigned long rv;
for (i = 4; i < 16; i++) {
if (!arch_get_random_seed_long_early(&rv) &&
!arch_get_random_long_early(&rv)) {
rv = random_get_entropy();
arch_init = false;
}
crng->state[i] ^= rv;
}
return arch_init;
}
static void crng_initialize_secondary(struct crng_state *crng)
{
chacha_init_consts(crng->state);
_get_random_bytes(&crng->state[4], sizeof(u32) * 12);
crng_init_try_arch(crng);
crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
}
static void __init crng_initialize_primary(struct crng_state *crng)
{
_extract_entropy(&crng->state[4], sizeof(u32) * 12);
if (crng_init_try_arch_early(crng) && trust_cpu && crng_init < 2) {
invalidate_batched_entropy();
numa_crng_init();
crng_init = 2;
pr_notice("crng init done (trusting CPU's manufacturer)\n");
}
crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
}
static void crng_finalize_init(struct crng_state *crng)
{
if (crng != &primary_crng || crng_init >= 2)
return;
if (!system_wq) {
/* We can't call numa_crng_init until we have workqueues,
* so mark this for processing later. */
crng_need_final_init = true;
return;
}
invalidate_batched_entropy();
numa_crng_init();
crng_init = 2;
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
pr_notice("crng init done\n");
if (unseeded_warning.missed) {
pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",
unseeded_warning.missed);
unseeded_warning.missed = 0;
}
if (urandom_warning.missed) {
pr_notice("%d urandom warning(s) missed due to ratelimiting\n",
urandom_warning.missed);
urandom_warning.missed = 0;
}
}
static void do_numa_crng_init(struct work_struct *work)
{
int i;
struct crng_state *crng;
struct crng_state **pool;
pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL | __GFP_NOFAIL);
for_each_online_node(i) {
crng = kmalloc_node(sizeof(struct crng_state),
GFP_KERNEL | __GFP_NOFAIL, i);
spin_lock_init(&crng->lock);
crng_initialize_secondary(crng);
pool[i] = crng;
}
/* pairs with READ_ONCE() in select_crng() */
if (cmpxchg_release(&crng_node_pool, NULL, pool) != NULL) {
for_each_node(i)
kfree(pool[i]);
kfree(pool);
}
}
static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);
static void numa_crng_init(void)
{
if (IS_ENABLED(CONFIG_NUMA))
schedule_work(&numa_crng_init_work);
}
static struct crng_state *select_crng(void)
{
if (IS_ENABLED(CONFIG_NUMA)) {
struct crng_state **pool;
int nid = numa_node_id();
/* pairs with cmpxchg_release() in do_numa_crng_init() */
pool = READ_ONCE(crng_node_pool);
if (pool && pool[nid])
return pool[nid];
}
return &primary_crng;
}
/*
* crng_fast_load() can be called by code in the interrupt service
* path. So we can't afford to dilly-dally. Returns the number of
* bytes processed from cp.
*/
static size_t crng_fast_load(const u8 *cp, size_t len)
{
unsigned long flags;
u8 *p;
size_t ret = 0;
if (!spin_trylock_irqsave(&primary_crng.lock, flags))
return 0;
if (crng_init != 0) {
spin_unlock_irqrestore(&primary_crng.lock, flags);
return 0;
}
p = (u8 *)&primary_crng.state[4];
while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) {
p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp;
cp++; crng_init_cnt++; len--; ret++;
}
spin_unlock_irqrestore(&primary_crng.lock, flags);
if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
invalidate_batched_entropy();
crng_init = 1;
pr_notice("fast init done\n");
}
return ret;
}
/*
* crng_slow_load() is called by add_device_randomness, which has two
* attributes. (1) We can't trust the buffer passed to it is
* guaranteed to be unpredictable (so it might not have any entropy at
* all), and (2) it doesn't have the performance constraints of
* crng_fast_load().
*
* So we do something more comprehensive which is guaranteed to touch
* all of the primary_crng's state, and which uses a LFSR with a
* period of 255 as part of the mixing algorithm. Finally, we do
* *not* advance crng_init_cnt since buffer we may get may be something
* like a fixed DMI table (for example), which might very well be
* unique to the machine, but is otherwise unvarying.
*/
static int crng_slow_load(const u8 *cp, size_t len)
{
unsigned long flags;
static u8 lfsr = 1;
u8 tmp;
unsigned int i, max = CHACHA_KEY_SIZE;
const u8 *src_buf = cp;
u8 *dest_buf = (u8 *)&primary_crng.state[4];
if (!spin_trylock_irqsave(&primary_crng.lock, flags))
return 0;
if (crng_init != 0) {
spin_unlock_irqrestore(&primary_crng.lock, flags);
return 0;
}
if (len > max)
max = len;
for (i = 0; i < max; i++) {
tmp = lfsr;
lfsr >>= 1;
if (tmp & 1)
lfsr ^= 0xE1;
tmp = dest_buf[i % CHACHA_KEY_SIZE];
dest_buf[i % CHACHA_KEY_SIZE] ^= src_buf[i % len] ^ lfsr;
lfsr += (tmp << 3) | (tmp >> 5);
}
spin_unlock_irqrestore(&primary_crng.lock, flags);
return 1;
}
static void crng_reseed(struct crng_state *crng, bool use_input_pool)
{
unsigned long flags;
int i, num;
union {
u8 block[CHACHA_BLOCK_SIZE];
u32 key[8];
} buf;
if (use_input_pool) {
num = extract_entropy(&buf, 32, 16);
if (num == 0)
return;
} else {
_extract_crng(&primary_crng, buf.block);
_crng_backtrack_protect(&primary_crng, buf.block,
CHACHA_KEY_SIZE);
}
spin_lock_irqsave(&crng->lock, flags);
for (i = 0; i < 8; i++) {
unsigned long rv;
if (!arch_get_random_seed_long(&rv) &&
!arch_get_random_long(&rv))
rv = random_get_entropy();
crng->state[i + 4] ^= buf.key[i] ^ rv;
}
memzero_explicit(&buf, sizeof(buf));
WRITE_ONCE(crng->init_time, jiffies);
spin_unlock_irqrestore(&crng->lock, flags);
crng_finalize_init(crng);
}
static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE])
{
unsigned long flags, init_time;
if (crng_ready()) {
init_time = READ_ONCE(crng->init_time);
if (time_after(READ_ONCE(crng_global_init_time), init_time) ||
time_after(jiffies, init_time + CRNG_RESEED_INTERVAL))
crng_reseed(crng, crng == &primary_crng);
}
spin_lock_irqsave(&crng->lock, flags);
chacha20_block(&crng->state[0], out);
if (crng->state[12] == 0)
crng->state[13]++;
spin_unlock_irqrestore(&crng->lock, flags);
}
static void extract_crng(u8 out[CHACHA_BLOCK_SIZE])
{
_extract_crng(select_crng(), out);
}
/*
* Use the leftover bytes from the CRNG block output (if there is
* enough) to mutate the CRNG key to provide backtracking protection.
*/
static void _crng_backtrack_protect(struct crng_state *crng,
u8 tmp[CHACHA_BLOCK_SIZE], int used)
{
unsigned long flags;
u32 *s, *d;
int i;
used = round_up(used, sizeof(u32));
if (used + CHACHA_KEY_SIZE > CHACHA_BLOCK_SIZE) {
extract_crng(tmp);
used = 0;
}
spin_lock_irqsave(&crng->lock, flags);
s = (u32 *)&tmp[used];
d = &crng->state[4];
for (i = 0; i < 8; i++)
*d++ ^= *s++;
spin_unlock_irqrestore(&crng->lock, flags);
}
static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used)
{
_crng_backtrack_protect(select_crng(), tmp, used);
}
static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
{
ssize_t ret = 0, i = CHACHA_BLOCK_SIZE;
u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4);
int large_request = (nbytes > 256);
while (nbytes) {
if (large_request && need_resched()) {
if (signal_pending(current)) {
if (ret == 0)
ret = -ERESTARTSYS;
break;
}
schedule();
}
extract_crng(tmp);
i = min_t(int, nbytes, CHACHA_BLOCK_SIZE);
if (copy_to_user(buf, tmp, i)) {
ret = -EFAULT;
break;
}
nbytes -= i;
buf += i;
ret += i;
}
crng_backtrack_protect(tmp, i);
/* Wipe data just written to memory */
memzero_explicit(tmp, sizeof(tmp));
return ret;
}
/*********************************************************************
*
* Entropy input management
*
*********************************************************************/
/* There is one of these per entropy source */
struct timer_rand_state {
cycles_t last_time;
long last_delta, last_delta2;
};
#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };
/*
* Add device- or boot-specific data to the input pool to help
* initialize it.
*
* None of this adds any entropy; it is meant to avoid the problem of
* the entropy 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;
if (!crng_ready() && size)
crng_slow_load(buf, size);
trace_add_device_randomness(size, _RET_IP_);
spin_lock_irqsave(&input_pool.lock, flags);
_mix_pool_bytes(buf, size);
_mix_pool_bytes(&time, sizeof(time));
spin_unlock_irqrestore(&input_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 {
long jiffies;
unsigned int cycles;
unsigned int num;
} sample;
long delta, delta2, delta3;
sample.jiffies = jiffies;
sample.cycles = random_get_entropy();
sample.num = num;
mix_pool_bytes(&sample, sizeof(sample));
/*
* 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.
*/
delta = sample.jiffies - READ_ONCE(state->last_time);
WRITE_ONCE(state->last_time, sample.jiffies);
delta2 = delta - READ_ONCE(state->last_delta);
WRITE_ONCE(state->last_delta, delta);
delta3 = delta2 - READ_ONCE(state->last_delta2);
WRITE_ONCE(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 estimate to 12 bits.
*/
credit_entropy_bits(min_t(int, fls(delta >> 1), 11));
}
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(POOL_ENTROPY_BITS());
}
EXPORT_SYMBOL_GPL(add_input_randomness);
static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
#ifdef ADD_INTERRUPT_BENCH
static unsigned long avg_cycles, avg_deviation;
#define AVG_SHIFT 8 /* Exponential average factor k=1/256 */
#define FIXED_1_2 (1 << (AVG_SHIFT - 1))
static void add_interrupt_bench(cycles_t start)
{
long delta = random_get_entropy() - start;
/* Use a weighted moving average */
delta = delta - ((avg_cycles + FIXED_1_2) >> AVG_SHIFT);
avg_cycles += delta;
/* And average deviation */
delta = abs(delta) - ((avg_deviation + FIXED_1_2) >> AVG_SHIFT);
avg_deviation += delta;
}
#else
#define add_interrupt_bench(x)
#endif
static u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
{
u32 *ptr = (u32 *)regs;
unsigned int idx;
if (regs == NULL)
return 0;
idx = READ_ONCE(f->reg_idx);
if (idx >= sizeof(struct pt_regs) / sizeof(u32))
idx = 0;
ptr += idx++;
WRITE_ONCE(f->reg_idx, idx);
return *ptr;
}
void add_interrupt_randomness(int irq)
{
struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
struct pt_regs *regs = get_irq_regs();
unsigned long now = jiffies;
cycles_t cycles = random_get_entropy();
u32 c_high, j_high;
u64 ip;
if (cycles == 0)
cycles = get_reg(fast_pool, regs);
c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
j_high = (sizeof(now) > 4) ? now >> 32 : 0;
fast_pool->pool[0] ^= cycles ^ j_high ^ irq;
fast_pool->pool[1] ^= now ^ c_high;
ip = regs ? instruction_pointer(regs) : _RET_IP_;
fast_pool->pool[2] ^= ip;
fast_pool->pool[3] ^=
(sizeof(ip) > 4) ? ip >> 32 : get_reg(fast_pool, regs);
fast_mix(fast_pool);
add_interrupt_bench(cycles);
if (unlikely(crng_init == 0)) {
if ((fast_pool->count >= 64) &&
crng_fast_load((u8 *)fast_pool->pool, sizeof(fast_pool->pool)) > 0) {
fast_pool->count = 0;
fast_pool->last = now;
}
return;
}
if ((fast_pool->count < 64) && !time_after(now, fast_pool->last + HZ))
return;
if (!spin_trylock(&input_pool.lock))
return;
fast_pool->last = now;
__mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool));
spin_unlock(&input_pool.lock);
fast_pool->count = 0;
/* award one bit for the contents of the fast pool */
credit_entropy_bits(1);
}
EXPORT_SYMBOL_GPL(add_interrupt_randomness);
#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), POOL_ENTROPY_BITS());
}
EXPORT_SYMBOL_GPL(add_disk_randomness);
#endif
/*********************************************************************
*
* Entropy extraction routines
*
*********************************************************************/
/*
* This function decides how many bytes to actually take from the
* given pool, and also debits the entropy count accordingly.
*/
static size_t account(size_t nbytes, int min)
{
int entropy_count, orig;
size_t ibytes, nfrac;
BUG_ON(input_pool.entropy_count > POOL_FRACBITS);
/* Can we pull enough? */
retry:
entropy_count = orig = READ_ONCE(input_pool.entropy_count);
if (WARN_ON(entropy_count < 0)) {
pr_warn("negative entropy count: count %d\n", entropy_count);
entropy_count = 0;
}
/* never pull more than available */
ibytes = min_t(size_t, nbytes, entropy_count >> (POOL_ENTROPY_SHIFT + 3));
if (ibytes < min)
ibytes = 0;
nfrac = ibytes << (POOL_ENTROPY_SHIFT + 3);
if ((size_t)entropy_count > nfrac)
entropy_count -= nfrac;
else
entropy_count = 0;
if (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig)
goto retry;
trace_debit_entropy(8 * ibytes);
if (ibytes && POOL_ENTROPY_BITS() < random_write_wakeup_bits) {
wake_up_interruptible(&random_write_wait);
kill_fasync(&fasync, SIGIO, POLL_OUT);
}
return ibytes;
}
/*
* This function does the actual extraction for extract_entropy.
*
* Note: we assume that .poolwords is a multiple of 16 words.
*/
static void extract_buf(u8 *out)
{
struct blake2s_state state __aligned(__alignof__(unsigned long));
u8 hash[BLAKE2S_HASH_SIZE];
unsigned long *salt;
unsigned long flags;
blake2s_init(&state, sizeof(hash));
/*
* If we have an architectural hardware random number
* generator, use it for BLAKE2's salt & personal fields.
*/
for (salt = (unsigned long *)&state.h[4];
salt < (unsigned long *)&state.h[8]; ++salt) {
unsigned long v;
if (!arch_get_random_long(&v))
break;
*salt ^= v;
}
/* Generate a hash across the pool */
spin_lock_irqsave(&input_pool.lock, flags);
blake2s_update(&state, (const u8 *)input_pool_data, POOL_BYTES);
blake2s_final(&state, hash); /* final zeros out state */
/*
* 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
* outputs), unless the hash function can be inverted. By
* mixing at least a hash worth of hash data back, we make
* brute-forcing the feedback as hard as brute-forcing the
* hash.
*/
__mix_pool_bytes(hash, sizeof(hash));
spin_unlock_irqrestore(&input_pool.lock, flags);
/* Note that EXTRACT_SIZE is half of hash size here, because above
* we've dumped the full length back into mixer. By reducing the
* amount that we emit, we retain a level of forward secrecy.
*/
memcpy(out, hash, EXTRACT_SIZE);
memzero_explicit(hash, sizeof(hash));
}
static ssize_t _extract_entropy(void *buf, size_t nbytes)
{
ssize_t ret = 0, i;
u8 tmp[EXTRACT_SIZE];
while (nbytes) {
extract_buf(tmp);
i = min_t(int, nbytes, EXTRACT_SIZE);
memcpy(buf, tmp, i);
nbytes -= i;
buf += i;
ret += i;
}
/* Wipe data just returned from memory */
memzero_explicit(tmp, sizeof(tmp));
return ret;
}
/*
* This function 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.
*/
static ssize_t extract_entropy(void *buf, size_t nbytes, int min)
{
trace_extract_entropy(nbytes, POOL_ENTROPY_BITS(), _RET_IP_);
nbytes = account(nbytes, min);
return _extract_entropy(buf, nbytes);
}
#define warn_unseeded_randomness(previous) \
_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous)
{
#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
const bool print_once = false;
#else
static bool print_once __read_mostly;
#endif
if (print_once || crng_ready() ||
(previous && (caller == READ_ONCE(*previous))))
return;
WRITE_ONCE(*previous, caller);
#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
print_once = true;
#endif
if (__ratelimit(&unseeded_warning))
printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n",
func_name, caller, crng_init);
}
/*
* 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(). In order to ensure
* that the randomness provided by this function is okay, the function
* wait_for_random_bytes() should be called and return 0 at least once
* at any point prior.
*/
static void _get_random_bytes(void *buf, int nbytes)
{
u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4);
trace_get_random_bytes(nbytes, _RET_IP_);
while (nbytes >= CHACHA_BLOCK_SIZE) {
extract_crng(buf);
buf += CHACHA_BLOCK_SIZE;
nbytes -= CHACHA_BLOCK_SIZE;
}
if (nbytes > 0) {
extract_crng(tmp);
memcpy(buf, tmp, nbytes);
crng_backtrack_protect(tmp, nbytes);
} else
crng_backtrack_protect(tmp, CHACHA_BLOCK_SIZE);
memzero_explicit(tmp, sizeof(tmp));
}
void get_random_bytes(void *buf, int nbytes)
{
static void *previous;
warn_unseeded_randomness(&previous);
_get_random_bytes(buf, nbytes);
}
EXPORT_SYMBOL(get_random_bytes);
/*
* Each time the timer fires, we expect that we got an unpredictable
* jump in the cycle counter. Even if the timer is running on another
* CPU, the timer activity will be touching the stack of the CPU that is
* generating entropy..
*
* Note that we don't re-arm the timer in the timer itself - we are
* happy to be scheduled away, since that just makes the load more
* complex, but we do not want the timer to keep ticking unless the
* entropy loop is running.
*
* So the re-arming always happens in the entropy loop itself.
*/
static void entropy_timer(struct timer_list *t)
{
credit_entropy_bits(1);
}
/*
* If we have an actual cycle counter, see if we can
* generate enough entropy with timing noise
*/
static void try_to_generate_entropy(void)
{
struct {
unsigned long now;
struct timer_list timer;
} stack;
stack.now = random_get_entropy();
/* Slow counter - or none. Don't even bother */
if (stack.now == random_get_entropy())
return;
timer_setup_on_stack(&stack.timer, entropy_timer, 0);
while (!crng_ready()) {
if (!timer_pending(&stack.timer))
mod_timer(&stack.timer, jiffies + 1);
mix_pool_bytes(&stack.now, sizeof(stack.now));
schedule();
stack.now = random_get_entropy();
}
del_timer_sync(&stack.timer);
destroy_timer_on_stack(&stack.timer);
mix_pool_bytes(&stack.now, sizeof(stack.now));
}
/*
* Wait for the urandom pool to be seeded and thus guaranteed to supply
* cryptographically secure random numbers. This applies to: the /dev/urandom
* device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
* family of functions. Using any of these functions without first calling
* this function forfeits the guarantee of security.
*
* Returns: 0 if the urandom pool has been seeded.
* -ERESTARTSYS if the function was interrupted by a signal.
*/
int wait_for_random_bytes(void)
{
if (likely(crng_ready()))
return 0;
do {
int ret;
ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
if (ret)
return ret > 0 ? 0 : ret;
try_to_generate_entropy();
} while (!crng_ready());
return 0;
}
EXPORT_SYMBOL(wait_for_random_bytes);
/*
* Returns whether or not the urandom pool has been seeded and thus guaranteed
* to supply cryptographically secure random numbers. This applies to: the
* /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
* ,u64,int,long} family of functions.
*
* Returns: true if the urandom pool has been seeded.
* false if the urandom pool has not been seeded.
*/
bool rng_is_initialized(void)
{
return crng_ready();
}
EXPORT_SYMBOL(rng_is_initialized);
/*
* Add a callback function that will be invoked when the nonblocking
* pool is initialised.
*
* returns: 0 if callback is successfully added
* -EALREADY if pool is already initialised (callback not called)
* -ENOENT if module for callback is not alive
*/
int add_random_ready_callback(struct random_ready_callback *rdy)
{
struct module *owner;
unsigned long flags;
int err = -EALREADY;
if (crng_ready())
return err;
owner = rdy->owner;
if (!try_module_get(owner))
return -ENOENT;
spin_lock_irqsave(&random_ready_list_lock, flags);
if (crng_ready())
goto out;
owner = NULL;
list_add(&rdy->list, &random_ready_list);
err = 0;
out:
spin_unlock_irqrestore(&random_ready_list_lock, flags);
module_put(owner);
return err;
}
EXPORT_SYMBOL(add_random_ready_callback);
/*
* Delete a previously registered readiness callback function.
*/
void del_random_ready_callback(struct random_ready_callback *rdy)
{
unsigned long flags;
struct module *owner = NULL;
spin_lock_irqsave(&random_ready_list_lock, flags);
if (!list_empty(&rdy->list)) {
list_del_init(&rdy->list);
owner = rdy->owner;
}
spin_unlock_irqrestore(&random_ready_list_lock, flags);
module_put(owner);
}
EXPORT_SYMBOL(del_random_ready_callback);
/*
* 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.
*
* Return number of bytes filled in.
*/
int __must_check get_random_bytes_arch(void *buf, int nbytes)
{
int left = nbytes;
u8 *p = buf;
trace_get_random_bytes_arch(left, _RET_IP_);
while (left) {
unsigned long v;
int chunk = min_t(int, left, sizeof(unsigned long));
if (!arch_get_random_long(&v))
break;
memcpy(p, &v, chunk);
p += chunk;
left -= chunk;
}
return nbytes - left;
}
EXPORT_SYMBOL(get_random_bytes_arch);
/*
* init_std_data - initialize pool with system data
*
* 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 init_std_data(void)
{
int i;
ktime_t now = ktime_get_real();
unsigned long rv;
mix_pool_bytes(&now, sizeof(now));
for (i = POOL_BYTES; i > 0; i -= sizeof(rv)) {
if (!arch_get_random_seed_long(&rv) &&
!arch_get_random_long(&rv))
rv = random_get_entropy();
mix_pool_bytes(&rv, sizeof(rv));
}
mix_pool_bytes(utsname(), sizeof(*(utsname())));
}
/*
* 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.
*/
int __init rand_initialize(void)
{
init_std_data();
if (crng_need_final_init)
crng_finalize_init(&primary_crng);
crng_initialize_primary(&primary_crng);
crng_global_init_time = jiffies;
if (ratelimit_disable) {
urandom_warning.interval = 0;
unseeded_warning.interval = 0;
}
return 0;
}
#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 urandom_read_nowarn(struct file *file, char __user *buf,
size_t nbytes, loff_t *ppos)
{
int ret;
nbytes = min_t(size_t, nbytes, INT_MAX >> (POOL_ENTROPY_SHIFT + 3));
ret = extract_crng_user(buf, nbytes);
trace_urandom_read(8 * nbytes, 0, POOL_ENTROPY_BITS());
return ret;
}
static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
loff_t *ppos)
{
static int maxwarn = 10;
if (!crng_ready() && maxwarn > 0) {
maxwarn--;
if (__ratelimit(&urandom_warning))
pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
current->comm, nbytes);
}
return urandom_read_nowarn(file, buf, nbytes, ppos);
}
static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
loff_t *ppos)
{
int ret;
ret = wait_for_random_bytes();
if (ret != 0)
return ret;
return urandom_read_nowarn(file, buf, nbytes, ppos);
}
static __poll_t random_poll(struct file *file, poll_table *wait)
{
__poll_t mask;
poll_wait(file, &crng_init_wait, wait);
poll_wait(file, &random_write_wait, wait);
mask = 0;
if (crng_ready())
mask |= EPOLLIN | EPOLLRDNORM;
if (POOL_ENTROPY_BITS() < random_write_wakeup_bits)
mask |= EPOLLOUT | EPOLLWRNORM;
return mask;
}
static int write_pool(const char __user *buffer, size_t count)
{
size_t bytes;
u32 t, buf[16];
const char __user *p = buffer;
while (count > 0) {
int b, i = 0;
bytes = min(count, sizeof(buf));
if (copy_from_user(&buf, p, bytes))
return -EFAULT;
for (b = bytes; b > 0; b -= sizeof(u32), i++) {
if (!arch_get_random_int(&t))
break;
buf[i] ^= t;
}
count -= bytes;
p += bytes;
mix_pool_bytes(buf, bytes);
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(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 = POOL_ENTROPY_BITS();
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;
return credit_entropy_bits_safe(ent_count);
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((const char __user *)p, size);
if (retval < 0)
return retval;
return credit_entropy_bits_safe(ent_count);
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;
return 0;
case RNDRESEEDCRNG:
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (crng_init < 2)
return -ENODATA;
crng_reseed(&primary_crng, true);
WRITE_ONCE(crng_global_init_time, jiffies - 1);
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,
.compat_ioctl = compat_ptr_ioctl,
.fasync = random_fasync,
.llseek = noop_llseek,
};
const struct file_operations urandom_fops = {
.read = urandom_read,
.write = random_write,
.unlocked_ioctl = random_ioctl,
.compat_ioctl = compat_ptr_ioctl,
.fasync = random_fasync,
.llseek = noop_llseek,
};
SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
flags)
{
int ret;
if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
return -EINVAL;
/*
* Requesting insecure and blocking randomness at the same time makes
* no sense.
*/
if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
return -EINVAL;
if (count > INT_MAX)
count = INT_MAX;
if (!(flags & GRND_INSECURE) && !crng_ready()) {
if (flags & GRND_NONBLOCK)
return -EAGAIN;
ret = wait_for_random_bytes();
if (unlikely(ret))
return ret;
}
return urandom_read_nowarn(NULL, buf, count, NULL);
}
/********************************************************************
*
* Sysctl interface
*
********************************************************************/
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
static int min_write_thresh;
static int max_write_thresh = POOL_BITS;
static int random_min_urandom_seed = 60;
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 *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(struct ctl_table *table, int write, void *buffer,
size_t *lenp, loff_t *ppos)
{
struct ctl_table fake_table;
int entropy_count;
entropy_count = *(int *)table->data >> POOL_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 = POOL_BITS;
static 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 = "write_wakeup_threshold",
.data = &random_write_wakeup_bits,
.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,
},
#ifdef ADD_INTERRUPT_BENCH
{
.procname = "add_interrupt_avg_cycles",
.data = &avg_cycles,
.maxlen = sizeof(avg_cycles),
.mode = 0444,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "add_interrupt_avg_deviation",
.data = &avg_deviation,
.maxlen = sizeof(avg_deviation),
.mode = 0444,
.proc_handler = proc_doulongvec_minmax,
},
#endif
{ }
};
/*
* rand_initialize() is called before sysctl_init(),
* so we cannot call register_sysctl_init() in rand_initialize()
*/
static int __init random_sysctls_init(void)
{
register_sysctl_init("kernel/random", random_table);
return 0;
}
device_initcall(random_sysctls_init);
#endif /* CONFIG_SYSCTL */
struct batched_entropy {
union {
u64 entropy_u64[CHACHA_BLOCK_SIZE / sizeof(u64)];
u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)];
};
unsigned int position;
spinlock_t batch_lock;
};
/*
* Get a random word for internal kernel use only. The quality of the random
* number is good as /dev/urandom, but there is no backtrack protection, with
* the goal of being quite fast and not depleting entropy. In order to ensure
* that the randomness provided by this function is okay, the function
* wait_for_random_bytes() should be called and return 0 at least once at any
* point prior.
*/
static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
.batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock),
};
u64 get_random_u64(void)
{
u64 ret;
unsigned long flags;
struct batched_entropy *batch;
static void *previous;
warn_unseeded_randomness(&previous);
batch = raw_cpu_ptr(&batched_entropy_u64);
spin_lock_irqsave(&batch->batch_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
extract_crng((u8 *)batch->entropy_u64);
batch->position = 0;
}
ret = batch->entropy_u64[batch->position++];
spin_unlock_irqrestore(&batch->batch_lock, flags);
return ret;
}
EXPORT_SYMBOL(get_random_u64);
static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
.batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock),
};
u32 get_random_u32(void)
{
u32 ret;
unsigned long flags;
struct batched_entropy *batch;
static void *previous;
warn_unseeded_randomness(&previous);
batch = raw_cpu_ptr(&batched_entropy_u32);
spin_lock_irqsave(&batch->batch_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
extract_crng((u8 *)batch->entropy_u32);
batch->position = 0;
}
ret = batch->entropy_u32[batch->position++];
spin_unlock_irqrestore(&batch->batch_lock, flags);
return ret;
}
EXPORT_SYMBOL(get_random_u32);
/* It's important to invalidate all potential batched entropy that might
* be stored before the crng is initialized, which we can do lazily by
* simply resetting the counter to zero so that it's re-extracted on the
* next usage. */
static void invalidate_batched_entropy(void)
{
int cpu;
unsigned long flags;
for_each_possible_cpu(cpu) {
struct batched_entropy *batched_entropy;
batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu);
spin_lock_irqsave(&batched_entropy->batch_lock, flags);
batched_entropy->position = 0;
spin_unlock(&batched_entropy->batch_lock);
batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu);
spin_lock(&batched_entropy->batch_lock);
batched_entropy->position = 0;
spin_unlock_irqrestore(&batched_entropy->batch_lock, flags);
}
}
/**
* randomize_page - Generate a random, page aligned address
* @start: The smallest acceptable address the caller will take.
* @range: The size of the area, starting at @start, within which the
* random address must fall.
*
* If @start + @range would overflow, @range is capped.
*
* NOTE: Historical use of randomize_range, which this replaces, presumed that
* @start was already page aligned. We now align it regardless.
*
* Return: A page aligned address within [start, start + range). On error,
* @start is returned.
*/
unsigned long randomize_page(unsigned long start, unsigned long range)
{
if (!PAGE_ALIGNED(start)) {
range -= PAGE_ALIGN(start) - start;
start = PAGE_ALIGN(start);
}
if (start > ULONG_MAX - range)
range = ULONG_MAX - start;
range >>= PAGE_SHIFT;
if (range == 0)
return start;
return start + (get_random_long() % range << PAGE_SHIFT);
}
/* Interface for in-kernel drivers of true hardware RNGs.
* Those devices may produce endless random bits and will be throttled
* when our pool is full.
*/
void add_hwgenerator_randomness(const char *buffer, size_t count,
size_t entropy)
{
if (unlikely(crng_init == 0)) {
size_t ret = crng_fast_load(buffer, count);
mix_pool_bytes(buffer, ret);
count -= ret;
buffer += ret;
if (!count || crng_init == 0)
return;
}
/* Suspend writing if we're above the trickle threshold.
* We'll be woken up again once below random_write_wakeup_thresh,
* or when the calling thread is about to terminate.
*/
wait_event_interruptible(random_write_wait,
!system_wq || kthread_should_stop() ||
POOL_ENTROPY_BITS() <= random_write_wakeup_bits);
mix_pool_bytes(buffer, count);
credit_entropy_bits(entropy);
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
/* Handle random seed passed by bootloader.
* If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
* it would be regarded as device data.
* The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
*/
void add_bootloader_randomness(const void *buf, unsigned int size)
{
if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
add_hwgenerator_randomness(buf, size, size * 8);
else
add_device_randomness(buf, size);
}
EXPORT_SYMBOL_GPL(add_bootloader_randomness);
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