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Message-ID: <1345060109-9187-152-git-send-email-paul.gortmaker@windriver.com>
Date: Wed, 15 Aug 2012 15:48:15 -0400
From: Paul Gortmaker <paul.gortmaker@...driver.com>
To: <stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: "Theodore Ts'o" <tytso@....edu>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [v2.6.34-stable 151/165] random: make 'add_interrupt_randomness()' do something sane
From: Theodore Ts'o <tytso@....edu>
-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
If you see a problem with using this for longterm, please comment.
-------------------
commit 775f4b297b780601e61787b766f306ed3e1d23eb upstream.
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 <ewust@...ch.edu>
Reported-by: Eric Wustrow <ewust@...ch.edu>
Reported-by: Nadia Heninger <nadiah@...ucsd.edu>
Reported-by: Zakir Durumeric <zakir@...ch.edu>
Reported-by: J. Alex Halderman <jhalderm@...ch.edu>.
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
[PG: minor adjustment required since .34 doesn't have f9e4989eb8
which renames "status" to "random" in kernel/irq/handle.c ]
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
drivers/char/random.c | 103 ++++++++++++++++++++++++++++++++++++++--------
drivers/mfd/ab3100-core.c | 2 -
include/linux/random.h | 2 +-
kernel/irq/handle.c | 7 ++--
4 files changed, 90 insertions(+), 24 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1b3544d..a104af3 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -127,18 +127,14 @@
*
* void add_input_randomness(unsigned int type, unsigned int code,
* unsigned int value);
- * void add_interrupt_randomness(int irq);
+ * void add_interrupt_randomness(int irq, int irq_flags);
*
* add_input_randomness() uses the input layer interrupt timing, as well as
* the event type information from the hardware.
*
- * add_interrupt_randomness() uses the inter-interrupt timing as random
- * inputs to the entropy pool. Note that not all interrupts are good
- * sources of randomness! For example, the timer interrupts is not a
- * good choice, because the periodicity of the interrupts is too
- * regular, and hence predictable to an attacker. Disk interrupts are
- * a better measure, since the timing of the disk interrupts are more
- * unpredictable.
+ * add_interrupt_randomness() uses the interrupt timing as random
+ * inputs to the entropy pool. Using the cycle counters and the irq source
+ * as inputs, it feeds the randomness roughly once a second.
*
* All of these routines try to estimate how many bits of randomness a
* particular randomness source. They do this by keeping track of the
@@ -241,6 +237,7 @@
#include <linux/percpu.h>
#include <linux/cryptohash.h>
#include <linux/fips.h>
+#include <linux/ptrace.h>
#ifdef CONFIG_GENERIC_HARDIRQS
# include <linux/irq.h>
@@ -249,6 +246,7 @@
#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
+#include <asm/irq_regs.h>
#include <asm/io.h>
/*
@@ -414,7 +412,9 @@ struct entropy_store {
spinlock_t lock;
unsigned add_ptr;
int entropy_count;
+ int entropy_total;
int input_rotate;
+ unsigned int initialized:1;
__u8 last_data[EXTRACT_SIZE];
};
@@ -447,6 +447,10 @@ static struct entropy_store nonblocking_pool = {
.pool = nonblocking_pool_data
};
+static __u32 const twist_table[8] = {
+ 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
+ 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
+
/*
* This function adds bytes into the entropy "pool". It does not
* update the entropy estimate. The caller should call
@@ -460,9 +464,6 @@ static struct entropy_store nonblocking_pool = {
static void mix_pool_bytes_extract(struct entropy_store *r, const void *in,
int nbytes, __u8 out[64])
{
- static __u32 const twist_table[8] = {
- 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
- 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
int input_rotate;
int wordmask = r->poolinfo->poolwords - 1;
@@ -521,6 +522,36 @@ static void mix_pool_bytes(struct entropy_store *r, const void *in, int bytes)
mix_pool_bytes_extract(r, in, bytes, NULL);
}
+struct fast_pool {
+ __u32 pool[4];
+ unsigned long last;
+ unsigned short count;
+ unsigned char rotate;
+ unsigned char last_timer_intr;
+};
+
+/*
+ * This is a fast mixing routine used by the interrupt randomness
+ * collector. It's hardcoded for an 128 bit pool and assumes that any
+ * locks that might be needed are taken by the caller.
+ */
+static void fast_mix(struct fast_pool *f, const void *in, int nbytes)
+{
+ const char *bytes = in;
+ __u32 w;
+ unsigned i = f->count;
+ unsigned input_rotate = f->rotate;
+
+ while (nbytes--) {
+ w = rol32(*bytes++, input_rotate & 31) ^ f->pool[i & 3] ^
+ f->pool[(i + 1) & 3];
+ f->pool[i & 3] = (w >> 3) ^ twist_table[w & 7];
+ input_rotate += (i++ & 3) ? 7 : 14;
+ }
+ f->count = i;
+ f->rotate = input_rotate;
+}
+
/*
* Credit (or debit) the entropy store with n bits of entropy
*/
@@ -544,6 +575,12 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
entropy_count = r->poolinfo->POOLBITS;
r->entropy_count = entropy_count;
+ if (!r->initialized && nbits > 0) {
+ r->entropy_total += nbits;
+ if (r->entropy_total > 128)
+ r->initialized = 1;
+ }
+
/* should we wake readers? */
if (r == &input_pool && entropy_count >= random_read_wakeup_thresh) {
wake_up_interruptible(&random_read_wait);
@@ -693,17 +730,48 @@ void add_input_randomness(unsigned int type, unsigned int code,
}
EXPORT_SYMBOL_GPL(add_input_randomness);
-void add_interrupt_randomness(int irq)
+static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
+
+void add_interrupt_randomness(int irq, int irq_flags)
{
- struct timer_rand_state *state;
+ struct entropy_store *r;
+ struct fast_pool *fast_pool = &__get_cpu_var(irq_randomness);
+ struct pt_regs *regs = get_irq_regs();
+ unsigned long now = jiffies;
+ __u32 input[4], cycles = get_cycles();
+
+ input[0] = cycles ^ jiffies;
+ input[1] = irq;
+ if (regs) {
+ __u64 ip = instruction_pointer(regs);
+ input[2] = ip;
+ input[3] = ip >> 32;
+ }
- state = get_timer_rand_state(irq);
+ fast_mix(fast_pool, input, sizeof(input));
- if (state == NULL)
+ if ((fast_pool->count & 1023) &&
+ !time_after(now, fast_pool->last + HZ))
return;
- DEBUG_ENT("irq event %d\n", irq);
- add_timer_randomness(state, 0x100 + irq);
+ fast_pool->last = now;
+
+ r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
+ mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool));
+ /*
+ * If we don't have a valid cycle counter, and we see
+ * back-to-back timer interrupts, then skip giving credit for
+ * any entropy.
+ */
+ if (cycles == 0) {
+ if (irq_flags & __IRQF_TIMER) {
+ if (fast_pool->last_timer_intr)
+ return;
+ fast_pool->last_timer_intr = 1;
+ } else
+ fast_pool->last_timer_intr = 0;
+ }
+ credit_entropy_bits(r, 1);
}
#ifdef CONFIG_BLOCK
@@ -964,6 +1032,7 @@ static void init_std_data(struct entropy_store *r)
spin_lock_irqsave(&r->lock, flags);
r->entropy_count = 0;
+ r->entropy_total = 0;
spin_unlock_irqrestore(&r->lock, flags);
now = ktime_get_real();
diff --git a/drivers/mfd/ab3100-core.c b/drivers/mfd/ab3100-core.c
index 4267a4d..2a193dc 100644
--- a/drivers/mfd/ab3100-core.c
+++ b/drivers/mfd/ab3100-core.c
@@ -378,8 +378,6 @@ static irqreturn_t ab3100_irq_handler(int irq, void *data)
u32 fatevent;
int err;
- add_interrupt_randomness(irq);
-
err = ab3100_get_register_page_interruptible(ab3100, AB3100_EVENTA1,
event_regs, 3);
if (err)
diff --git a/include/linux/random.h b/include/linux/random.h
index 0bf2936..8a85602 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -48,7 +48,7 @@ extern void rand_initialize_irq(int irq);
extern void add_input_randomness(unsigned int type, unsigned int code,
unsigned int value);
-extern void add_interrupt_randomness(int irq);
+extern void add_interrupt_randomness(int irq, int irq_flags);
extern void get_random_bytes(void *buf, int nbytes);
void generate_random_uuid(unsigned char uuid_out[16]);
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 76d5a67..86bcf10 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -368,7 +368,7 @@ static void warn_no_thread(unsigned int irq, struct irqaction *action)
irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
{
irqreturn_t ret, retval = IRQ_NONE;
- unsigned int status = 0;
+ unsigned int flags = 0;
if (!(action->flags & IRQF_DISABLED))
local_irq_enable_in_hardirq();
@@ -411,7 +411,7 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
/* Fall through to add to randomness */
case IRQ_HANDLED:
- status |= action->flags;
+ flags |= action->flags;
break;
default:
@@ -422,8 +422,7 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
action = action->next;
} while (action);
- if (status & IRQF_SAMPLE_RANDOM)
- add_interrupt_randomness(irq);
+ add_interrupt_randomness(irq, flags);
local_irq_disable();
return retval;
--
1.7.12.rc2
--
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