This is a fairly simple driver that just starts up a kernel thread that
periodically calls the active clocksource's entropy-gathering function,
if it has one. The default interval of 100us between polls doesn't show
any measurable impact to cpu usage on a core 2 duo test rig here, and
ensures the entropy pool is constantly being fed, even on a system with
no input device, no network traffic and no disk activity.
CC: Matt Mackall <m...@selenic.com>
CC: "Venkatesh Pallipadi (Venki)" <ve...@google.com>
CC: Thomas Gleixner <t...@linutronix.de>
CC: Ingo Molnar <mi...@elte.hu>
CC: John Stultz <johns...@us.ibm.com>
CC: Herbert Xu <herb...@gondor.apana.org.au>
CC: "David S. Miller" <da...@davemloft.net>
Signed-off-by: Jarod Wilson <ja...@redhat.com>
---
drivers/misc/Kconfig | 14 +++++
drivers/misc/Makefile | 1 +
drivers/misc/clock-entropy.c | 122 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 137 insertions(+), 0 deletions(-)
create mode 100644 drivers/misc/clock-entropy.c
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 4e349cd..b997f6a 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -490,6 +490,20 @@ config PCH_PHUB
To compile this driver as a module, choose M here: the module will
be called pch_phub.
+config CLOCK_ENTROPY
+ tristate "Clocksource-based Entropy Generator"
+ help
+ This is a driver that simply starts up a kernel thread that calls
+ clocksource helper functions to periodically poll the clocksource,
+ calculate a delta from the prior poll, and then feed the delta
+ value along to the random number generator entropy pool. This can
+ be useful for server systems that are otherwise starved for entropy,
+ as there are very few sources of entropy generation, particularly
+ on a non-busy server system.
+
+ To compile this driver as a module, choose M here. The module will
+ be called clock-entropy.
+
source "drivers/misc/c2port/Kconfig"
source "drivers/misc/eeprom/Kconfig"
source "drivers/misc/cb710/Kconfig"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 5f03172..a659ad2 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -46,3 +46,4 @@ obj-y += ti-st/
obj-$(CONFIG_AB8500_PWM) += ab8500-pwm.o
obj-y += lis3lv02d/
obj-y += carma/
+obj-$(CONFIG_CLOCK_ENTROPY) += clock-entropy.o
diff --git a/drivers/misc/clock-entropy.c b/drivers/misc/clock-entropy.c
new file mode 100644
index 0000000..56d65ac
--- /dev/null
+++ b/drivers/misc/clock-entropy.c
@@ -0,0 +1,122 @@
+/*
+ * Clocksource-based entropy generator
+ * Copyright (c) 2011 Jarod Wilson <ja...@redhat.com>
+ *
+ * Many server systems are seriously lacking in sources of entropy,
+ * as we typically only feed the entropy pool by way of input layer
+ * events, a few NIC driver interrupts and disk activity. A non-busy
+ * server can easily become entropy-starved. We can mitigate this
+ * somewhat by periodically mixing in entropy data based on the
+ * delta between multiple high-resolution clocksource reads, per:
+ *
+ *
https://www.osadl.org/Analysis-of-inherent-randomness-of-the-L.rtlws11-developers-okech.0.html
+ *
+ * Additionally, NIST already approves of similar implementations, so
+ * this should be usable in high-securtiy deployments requiring a
+ * fair chunk of available entropy data for frequent use of /dev/random.
+ * ---
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/errno.h>
+#include <linux/kthread.h>
+#include <linux/clocksource.h>
+
+/* module parameters */
+static int ce_debug;
+static int interval = 100; /* microseconds */
+
+#define ce_dbg(fmt, args...) \
+ do { \
+ if (ce_debug) \
+ printk(KERN_DEBUG KBUILD_MODNAME ": " fmt, \
+ ## args); \
+ } while (0)
+
+/* Periodic clocksource polling thread data */
+static struct task_struct *ceg_task;
+
+/**
+ * If the current clocksource doesn't have an entropy-generation function
+ * wired up, this thread will do absolutely nothing productive, but we
+ * leave it running, in the event clocksources are changed to one of the
+ * ones that can provide entropy. We've already verified there's one that
+ * can by way of clocksource_entropy_available at init time.
+ */
+static int ceg_thread(void *arg)
+{
+ signed long timeout = usecs_to_jiffies(interval);
+
+ ce_dbg("polling thread started\n");
+
+ while (!kthread_should_stop()) {
+ set_current_state(TASK_INTERRUPTIBLE);
+
+ schedule_timeout(timeout);
+ if (kthread_should_stop())
+ break;
+
+ clocksource_add_entropy();
+ }
+
+ ce_dbg("polling thread ended\n");
+
+ return 0;
+}
+
+static int __init ceg_init(void)
+{
+ if (!clocksource_entropy_available()) {
+ pr_err(KBUILD_MODNAME ": no clocksource entropy available\n");
+ return -EINVAL;
+ }
+
+ ceg_task = kthread_run(ceg_thread, NULL, "kclock-entropy-gen");
+ if (IS_ERR(ceg_task)) {
+ pr_err(KBUILD_MODNAME ": failed to initialize kthread\n");
+ return PTR_ERR(ceg_task);
+ }
+
+ ce_dbg("Clocksource Entropy Generator initialized\n");
+
+ return 0;
+}
+
+static void __exit ceg_exit(void)
+{
+ if (!IS_ERR_OR_NULL(ceg_task)) {
+ kthread_stop(ceg_task);
+ ceg_task = NULL;
+ }
+
+ ce_dbg("Clocksource Entropy Generator unloaded\n");
+}
+
+module_init(ceg_init);
+module_exit(ceg_exit);
+
+MODULE_DESCRIPTION("Clocksource-based entropy generator");
+MODULE_AUTHOR("Jarod Wilson <ja...@redhat.com>");
+MODULE_LICENSE("GPL");
+
+module_param(ce_debug, bool, 0644);
+MODULE_PARM_DESC(ce_debug, "Enable debugging messages");
+
+module_param(interval, int, 0644);
+MODULE_PARM_DESC(interval, "Clocksource sampling interval, in microseconds
(default: 100us)");
--
1.7.1
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