diff options
| -rw-r--r-- | drivers/char/random.c | 36 |
1 files changed, 26 insertions, 10 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index 6229d7d3c5b5..bd6fdb624861 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1354,6 +1354,12 @@ void add_interrupt_randomness(int irq) } EXPORT_SYMBOL_GPL(add_interrupt_randomness); +struct entropy_timer_state { + unsigned long entropy; + struct timer_list timer; + unsigned int samples, samples_per_bit; +}; + /* * 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 @@ -1367,9 +1373,14 @@ EXPORT_SYMBOL_GPL(add_interrupt_randomness); * * So the re-arming always happens in the entropy loop itself. */ -static void entropy_timer(struct timer_list *t) +static void entropy_timer(struct timer_list *timer) { - credit_entropy_bits(1); + struct entropy_timer_state *state = container_of(timer, struct entropy_timer_state, timer); + + if (++state->samples == state->samples_per_bit) { + credit_entropy_bits(1); + state->samples = 0; + } } /* @@ -1378,17 +1389,22 @@ static void entropy_timer(struct timer_list *t) */ static void try_to_generate_entropy(void) { - struct { - unsigned long entropy; - struct timer_list timer; - } stack; - - stack.entropy = random_get_entropy(); + enum { NUM_TRIAL_SAMPLES = 8192, MAX_SAMPLES_PER_BIT = 32 }; + struct entropy_timer_state stack; + unsigned int i, num_different = 0; + unsigned long last = random_get_entropy(); - /* Slow counter - or none. Don't even bother */ - if (stack.entropy == random_get_entropy()) + for (i = 0; i < NUM_TRIAL_SAMPLES - 1; ++i) { + stack.entropy = random_get_entropy(); + if (stack.entropy != last) + ++num_different; + last = stack.entropy; + } + stack.samples_per_bit = DIV_ROUND_UP(NUM_TRIAL_SAMPLES, num_different + 1); + if (stack.samples_per_bit > MAX_SAMPLES_PER_BIT) return; + stack.samples = 0; timer_setup_on_stack(&stack.timer, entropy_timer, 0); while (!crng_ready() && !signal_pending(current)) { if (!timer_pending(&stack.timer)) |