From: Matt Mackall <mpm@selenic.com>
The input layer is now sending us a bunch of events in a row for each actual
event. This shows up weaknesses in the periodicity detector and using the
high clock rate from get_clock: each keystroke is getting accounted as 10
different maximal-entropy events.
A brief touch on a trackpad will generate as much as 2000 maximal entropy
events which is more than 2k of /dev/random output. IOW, we're WAY
overestimating input entropy. Here's one keystroke:
random 0024 0000 0000: mouse event
random 0035 0000 0000: added 11 entropy credits to input
random 0035 0000 0000: mouse event
random 0046 0000 0000: added 11 entropy credits to input
random 0046 0000 0000: mouse event
random 0056 0000 0000: added 10 entropy credits to input
random 0056 0000 0000: keyboard event
random 0067 0000 0000: added 11 entropy credits to input
random 0067 0000 0000: mouse event
random 0078 0000 0000: added 11 entropy credits to input
random 0078 0000 0000: awake
random 0078 0000 0000: reading 128 bits
random 0078 0000 0000: going to reseed blocking with 128 bits (128 of 0 requested)
random 0078 0000 0000: trying to extract 128 bits from input
random 0006 0000 0000: debiting 72 entropy credits from input
random 0006 0072 0000: added 72 entropy credits to blocking
random 0006 0072 0000: trying to extract 128 bits from blocking
random 0006 0000 0000: debiting 72 entropy credits from blocking
random 0006 0000 0000: read got 72 bits (56 still needed)
random 0006 0000 0000: reading 56 bits
random 0006 0000 0000: going to reseed blocking with 64 bits (56 of 0 requested
random 0006 0000 0000: trying to extract 64 bits from input
random 0006 0000 0000: debiting 0 entropy credits from input
random 0006 0000 0000: trying to extract 56 bits from blocking
random 0006 0000 0000: debiting 0 entropy credits from blocking
random 0006 0000 0000: read got 0 bits (56 still needed)
random 0006 0000 0000: sleeping
random 0006 0000 0000: mouse event
random 0017 0000 0000: added 11 entropy credits to input
random 0017 0000 0000: mouse event
random 0028 0000 0000: added 11 entropy credits to input
random 0028 0000 0000: mouse event
random 0038 0000 0000: added 10 entropy credits to input
random 0038 0000 0000: keyboard event
random 0049 0000 0000: added 11 entropy credits to input
random 0049 0000 0000: mouse event
random 0060 0000 0000: added 11 entropy credits to input
The first step to fixing this is to check periodicity and estimate entropy
against a slow clock like jiffies. We continue to mix in get_clock() rather
than jiffies where available.
This throws away most of the duplicate events and gives us more sensible
entropy estimates, but we still duplicates from input.c and keyboard.c.
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/char/random.c | 29 ++++++++++++++++-------------
1 files changed, 16 insertions(+), 13 deletions(-)
diff -puN drivers/char/random.c~random-periodicity-detection-fix drivers/char/random.c
--- 25/drivers/char/random.c~random-periodicity-detection-fix 2005-01-12 23:16:40.368035968 -0800
+++ 25-akpm/drivers/char/random.c 2005-01-12 23:16:40.375034904 -0800
@@ -805,8 +805,8 @@ static struct timer_rand_state *irq_time
*/
static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
{
- cycles_t time;
- long delta, delta2, delta3;
+ cycles_t data;
+ long delta, delta2, delta3, time;
int entropy = 0;
preempt_disable();
@@ -816,20 +816,12 @@ static void add_timer_randomness(struct
goto out;
/*
- * Use get_cycles() if implemented, otherwise fall back to
- * jiffies.
- */
- time = get_cycles();
- if (time)
- num ^= (u32)((time >> 31) >> 1);
- else
- time = jiffies;
-
- /*
* Calculate number of bits of randomness we probably added.
* We take into account the first, second and third-order deltas
* in order to make our estimate.
*/
+ time = jiffies;
+
if (!state->dont_count_entropy) {
delta = time - state->last_time;
state->last_time = time;
@@ -861,7 +853,18 @@ static void add_timer_randomness(struct
entropy = int_ln_12bits(delta);
}
- batch_entropy_store(num, time, entropy);
+
+ /*
+ * Use get_cycles() if implemented, otherwise fall back to
+ * jiffies.
+ */
+ data = get_cycles();
+ if (data)
+ num ^= (u32)((data >> 31) >> 1);
+ else
+ data = time;
+
+ batch_entropy_store(num, data, entropy);
out:
preempt_enable();
}
_