Commit 83664a69 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Theodore Ts'o
Browse files

random: Use arch_get_random_seed*() at init time and once a second 



Use arch_get_random_seed*() in two places in the Linux random
driver (drivers/char/random.c):

1. During entropy pool initialization, use RDSEED in favor of RDRAND,
   with a fallback to the latter.  Entropy exhaustion is unlikely to
   happen there on physical hardware as the machine is single-threaded
   at that point, but could happen in a virtual machine.  In that
   case, the fallback to RDRAND will still provide more than adequate
   entropy pool initialization.

2. Once a second, issue RDSEED and, if successful, feed it to the
   entropy pool.  To ensure an extra layer of security, only credit
   half the entropy just in case.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent d20f78d2

drivers/char/random.c

+20 −4
Original line number Diff line number Diff line
@@ -844,6 +844,8 @@ void add_interrupt_randomness(int irq, int irq_flags) 
	cycles_t		cycles = random_get_entropy();

	__u32			input[4], c_high, j_high;

	__u64			ip;

	unsigned long		seed;

	int			credit;



	c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;

	j_high = (sizeof(now) > 4) ? now >> 32 : 0;
@@ -862,20 +864,33 @@ void add_interrupt_randomness(int irq, int irq_flags) 


	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.

	 * any entropy, otherwise credit 1 bit.

	 */

	credit = 1;

	if (cycles == 0) {

		if (irq_flags & __IRQF_TIMER) {

			if (fast_pool->last_timer_intr)

				return;

				credit = 0;

			fast_pool->last_timer_intr = 1;

		} else

			fast_pool->last_timer_intr = 0;

	}

	credit_entropy_bits(r, 1);



	/*

	 * If we have architectural seed generator, produce a seed and

	 * add it to the pool.  For the sake of paranoia count it as

	 * 50% entropic.

	 */

	if (arch_get_random_seed_long(&seed)) {

		__mix_pool_bytes(r, &seed, sizeof(seed), NULL);

		credit += sizeof(seed) * 4;

	}



	credit_entropy_bits(r, credit);

}



#ifdef CONFIG_BLOCK
@@ -1235,7 +1250,8 @@ static void init_std_data(struct entropy_store *r) 
	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))

		if (!arch_get_random_seed_long(&rv) &&

		    !arch_get_random_long(&rv))

			rv = random_get_entropy();

		mix_pool_bytes(r, &rv, sizeof(rv), NULL);

	}

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