random32: add a selftest for the prandom32 code

#include <linux/jiffies.h>

#include <linux/random.h>

#include <linux/sched.h>

#include <linux/bitops.h>

#include <asm/unaligned.h>

#include <trace/events/random.h>

	mod_timer(&seed_timer, jiffies);

}

#ifdef CONFIG_RANDOM32_SELFTEST

/* Principle: True 32-bit random numbers will all have 16 differing bits on

 * average. For each 32-bit number, there are 601M numbers differing by 16

 * bits, and 89% of the numbers differ by at least 12 bits. Note that more

 * than 16 differing bits also implies a correlation with inverted bits. Thus

 * we take 1024 random numbers and compare each of them to the other ones,

 * counting the deviation of correlated bits to 16. Constants report 32,

 * counters 32-log2(TEST_SIZE), and pure randoms, around 6 or lower. With the

 * u32 total, TEST_SIZE may be as large as 4096 samples.

 */

#define TEST_SIZE 1024

static int __init prandom32_state_selftest(void)

{

	unsigned int x, y, bits, samples;

	u32 xor, flip;

	u32 total;

	u32 *data;

	data = kmalloc(sizeof(*data) * TEST_SIZE, GFP_KERNEL);

	if (!data)

		return 0;

	for (samples = 0; samples < TEST_SIZE; samples++)

		data[samples] = prandom_u32();

	flip = total = 0;

	for (x = 0; x < samples; x++) {

		for (y = 0; y < samples; y++) {

			if (x == y)

				continue;

			xor = data[x] ^ data[y];

			flip |= xor;

			bits = hweight32(xor);

			total += (bits - 16) * (bits - 16);

		}

	}

	/* We'll return the average deviation as 2*sqrt(corr/samples), which

	 * is also sqrt(4*corr/samples) which provides a better resolution.

	 */

	bits = int_sqrt(total / (samples * (samples - 1)) * 4);

	if (bits > 6)

		pr_warn("prandom32: self test failed (at least %u bits"

			" correlated, fixed_mask=%#x fixed_value=%#x\n",

			bits, ~flip, data[0] & ~flip);

	else

		pr_info("prandom32: self test passed (less than %u bits"

			" correlated)\n",

			bits+1);

	kfree(data);

	return 0;

}

core_initcall(prandom32_state_selftest);

#endif /*  CONFIG_RANDOM32_SELFTEST */

/*

 * Start periodic full reseeding as soon as strong

 * random numbers are available.