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

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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: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
H. Peter Anvin 2014-03-17 16:36:28 -07:00 committed by Theodore Ts'o
parent d20f78d252
commit 83664a6928
1 changed files with 20 additions and 4 deletions
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24
drivers/char/random.c
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@ -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);
}