87 lines
2.5 KiB
Diff
87 lines
2.5 KiB
Diff
Try to actively add entropy instead of waiting forever.
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Fixes <https://bugs.gnu.org/37501>.
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Taken from upstream:
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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=50ee7529ec4500c88f8664560770a7a1b65db72b
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diff --git a/drivers/char/random.c b/drivers/char/random.c
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index 5d5ea4ce1442..2fda6166c1dd 100644
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--- a/drivers/char/random.c
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+++ b/drivers/char/random.c
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@@ -1731,6 +1731,56 @@ void get_random_bytes(void *buf, int nbytes)
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}
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EXPORT_SYMBOL(get_random_bytes);
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+
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+/*
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+ * Each time the timer fires, we expect that we got an unpredictable
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+ * jump in the cycle counter. Even if the timer is running on another
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+ * CPU, the timer activity will be touching the stack of the CPU that is
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+ * generating entropy..
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+ *
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+ * Note that we don't re-arm the timer in the timer itself - we are
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+ * happy to be scheduled away, since that just makes the load more
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+ * complex, but we do not want the timer to keep ticking unless the
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+ * entropy loop is running.
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+ *
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+ * So the re-arming always happens in the entropy loop itself.
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+ */
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+static void entropy_timer(struct timer_list *t)
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+{
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+ credit_entropy_bits(&input_pool, 1);
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+}
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+
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+/*
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+ * If we have an actual cycle counter, see if we can
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+ * generate enough entropy with timing noise
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+ */
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+static void try_to_generate_entropy(void)
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+{
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+ struct {
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+ unsigned long now;
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+ struct timer_list timer;
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+ } stack;
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+
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+ stack.now = random_get_entropy();
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+
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+ /* Slow counter - or none. Don't even bother */
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+ if (stack.now == random_get_entropy())
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+ return;
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+
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+ timer_setup_on_stack(&stack.timer, entropy_timer, 0);
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+ while (!crng_ready()) {
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+ if (!timer_pending(&stack.timer))
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+ mod_timer(&stack.timer, jiffies+1);
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+ mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now));
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+ schedule();
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+ stack.now = random_get_entropy();
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+ }
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+
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+ del_timer_sync(&stack.timer);
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+ destroy_timer_on_stack(&stack.timer);
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+ mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now));
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+}
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+
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/*
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* Wait for the urandom pool to be seeded and thus guaranteed to supply
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* cryptographically secure random numbers. This applies to: the /dev/urandom
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@@ -1745,7 +1795,17 @@ int wait_for_random_bytes(void)
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{
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if (likely(crng_ready()))
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return 0;
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- return wait_event_interruptible(crng_init_wait, crng_ready());
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+
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+ do {
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+ int ret;
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+ ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
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+ if (ret)
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+ return ret > 0 ? 0 : ret;
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+
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+ try_to_generate_entropy();
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+ } while (!crng_ready());
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+
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+ return 0;
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}
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EXPORT_SYMBOL(wait_for_random_bytes);
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