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random: make 'add_interrupt_randomness()' do something sane

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We've been moving away from add_interrupt_randomness() for various
reasons: it's too expensive to do on every interrupt, and flooding the
CPU with interrupts could theoretically cause bogus floods of entropy
from a somewhat externally controllable source.

This solves both problems by limiting the actual randomness addition
to just once a second or after 64 interrupts, whicever comes first.
During that time, the interrupt cycle data is buffered up in a per-cpu
pool.  Also, we make sure the the nonblocking pool used by urandom is
initialized before we start feeding the normal input pool.  This
assures that /dev/urandom is returning unpredictable data as soon as
possible.

(Based on an original patch by Linus, but significantly modified by
tytso.)

Tested-by: Eric Wustrow <[email protected]>
Reported-by: Eric Wustrow <[email protected]>
Reported-by: Nadia Heninger <[email protected]>
Reported-by: Zakir Durumeric <[email protected]>
Reported-by: J. Alex Halderman <[email protected]>.
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: "Theodore Ts'o" <[email protected]>
Cc: [email protected]
This commit is contained in:
Theodore Ts'o 2012-07-02 07:52:16 -04:00
commit 775f4b297b
4 changed files with 90 additions and 24 deletions
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7
kernel/irq/handle.c
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@ -133,7 +133,7 @@ irqreturn_t
handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
{
irqreturn_t retval = IRQ_NONE;
unsigned int random = 0, irq = desc->irq_data.irq;
unsigned int flags = 0, irq = desc->irq_data.irq;
do {
irqreturn_t res;
@ -161,7 +161,7 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
/* Fall through to add to randomness */
case IRQ_HANDLED:
random |= action->flags;
flags |= action->flags;
break;
default:
@ -172,8 +172,7 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
action = action->next;
} while (action);
if (random & IRQF_SAMPLE_RANDOM)
add_interrupt_randomness(irq);
add_interrupt_randomness(irq, flags);
if (!noirqdebug)
note_interrupt(irq, desc, retval);