diff options
| -rw-r--r-- | drivers/char/random.c | 62 |
1 files changed, 61 insertions, 1 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index 5d5ea4ce1442..2fda6166c1dd 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1731,6 +1731,56 @@ void get_random_bytes(void *buf, int 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(&input_pool, 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(&input_pool, &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(&input_pool, &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 @@ -1745,7 +1795,17 @@ int wait_for_random_bytes(void) { if (likely(crng_ready())) return 0; - return wait_event_interruptible(crng_init_wait, crng_ready()); + + 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); |