1) example (partially humorous random_adaptor, that I call "EXAMPLE")

 * It's not meant to be used in a real system, it's there to show how
   the basics of how to create interfaces for random_adaptors. Perhaps
   it should belong in a manual page

2) Move probe.c's functionality in to random_adaptors.c
 * rename random_ident_hardware() to random_adaptor_choose()

3) Introduce a new way to choose (or select) random_adaptors via tunable
"rngs_want" It's a list of comma separated names of adaptors, ordered
by preferences. I.e.:
rngs_want="yarrow,rdrand"

Such setting would cause yarrow to be preferred to rdrand. If neither of
them are available (or registered), then system will default to
something reasonable (currently yarrow). If yarrow is not present, then
we fall back to the adaptor that's first on the list of registered
adaptors.

4) Introduce a way where RNGs can play a role of entropy source. This is
mostly useful for HW rngs.

The way I envision this is that every HW RNG will use this
functionality by default. Functionality to disable this is also present.
I have an example of how to use this in random_adaptor_example.c (see
modload event, and init function)

5) fix kern.random.adaptors from
kern.random.adaptors: yarrowpanicblock
to
kern.random.adaptors: yarrow,panic,block

6) add kern.random.active_adaptor to indicate currently selected
adaptor:
root@freebsd04:~ # sysctl kern.random.active_adaptor
kern.random.active_adaptor: yarrow

Submitted by:	Arthur Mesh <arthurmesh@gmail.com>

1 files changed, 219 insertions, 9 deletions

diff --git a/sys/dev/random/random_adaptors.c b/sys/dev/random/random_adaptors.c
index c187bdb..b017993 100644
--- a/sys/dev/random/random_adaptors.c
+++ b/sys/dev/random/random_adaptors.c
@@ -1,6 +1,7 @@
 /*-
  * Copyright (c) 2013 Arthur Mesh <arthurmesh@gmail.com>
  * Copyright (c) 2013 David E. O'Brien <obrien@NUXI.org>
+ * Copyright (c) 2004 Mark R V Murray
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -30,16 +31,20 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/kernel.h>
 #include <sys/systm.h>
+#include <sys/kthread.h>
 #include <sys/lock.h>
+#include <sys/random.h>
 #include <sys/selinfo.h>
 #include <sys/sysctl.h>
 #include <sys/sx.h>
 #include <sys/malloc.h>
 #include <sys/queue.h>
 #include <sys/libkern.h>
+#include <sys/unistd.h>
 
-#include <dev/random/random_adaptors.h>
 #include <dev/random/randomdev.h>
+#include <dev/random/randomdev_soft.h>
+#include <dev/random/random_adaptors.h>
 
 LIST_HEAD(adaptors_head, random_adaptors);
 static struct adaptors_head adaptors = LIST_HEAD_INITIALIZER(adaptors);
@@ -50,6 +55,11 @@ static struct sysctl_ctx_list random_clist;
 
 MALLOC_DEFINE(M_RANDOM_ADAPTORS, "random_adaptors", "Random adaptors buffers");
 
+struct entropy_thread_ctx {
+	 struct random_adaptor   *adaptor;
+	 int			 *control;
+};
+
 int
 random_adaptor_register(const char *name, struct random_adaptor *rsp)
 {
@@ -57,7 +67,8 @@ random_adaptor_register(const char *name, struct random_adaptor *rsp)
 
 	KASSERT(name != NULL && rsp != NULL, ("invalid input to %s", __func__));
 
-	rpp = malloc(sizeof(struct random_adaptors), M_RANDOM_ADAPTORS, M_WAITOK);
+	rpp = malloc(sizeof(struct random_adaptors), M_RANDOM_ADAPTORS,
+	    M_WAITOK);
 	rpp->name = name;
 	rpp->rsp = rsp;
 
@@ -87,6 +98,159 @@ random_adaptor_get(const char *name)
 	return (rsp);
 }
 
+/*
+ * In the past, the logic of the random_adaptor selection was inverted, such
+ * that hardware RNGs would be chosen unless disabled. This routine is here to
+ * preserve that functionality to avoid folks losing their hardware RNGs by
+ * upgrading to newer kernel.
+ */
+static void
+random_adaptor_choose_legacy(struct random_adaptor **adaptor)
+{
+	struct random_adaptor *tmp;
+	int enable;
+
+	/* Then go looking for hardware */
+	enable = 1;
+	TUNABLE_INT_FETCH("hw.nehemiah_rng_enable", &enable);
+	if (enable && (tmp = random_adaptor_get("nehemiah")))
+		*adaptor = tmp;
+
+	enable = 1;
+	TUNABLE_INT_FETCH("hw.ivy_rng_enable", &enable);
+	if (enable && (tmp = random_adaptor_get("rdrand")))
+		*adaptor = tmp;
+}
+
+/*
+ * Walk a list of registered random(4) adaptors and pick the last non-selected
+ * one.
+ *
+ * If none are selected, use yarrow if available.
+ */
+void
+random_adaptor_choose(struct random_adaptor **adaptor)
+{
+	char			 rngs[128], *token, *cp;
+	struct random_adaptors  *rpp;
+
+	KASSERT(adaptor != NULL, ("pre-conditions failed"));
+
+	*adaptor = NULL;
+
+	random_adaptor_choose_legacy(adaptor);
+
+	if (*adaptor != NULL)
+		return;
+
+	if (TUNABLE_STR_FETCH("rngs_want", rngs, sizeof(rngs))) {
+		cp = rngs;
+
+		while ((token = strsep(&cp, ",")) != NULL) {
+			if ((*adaptor = random_adaptor_get(token)) != NULL)
+				break;
+			else if (bootverbose)
+				printf(
+			    "%s random adaptor is not available, skipping\n",
+				    token);
+		}
+	}
+
+	if (*adaptor == NULL) {
+		/*
+		 * Either no RNGs are prefered via rngs_want tunable, or
+		 * no prefered RNGs are registered.
+		 * Fallback to Yarrow.
+		 */
+		*adaptor = random_adaptor_get("yarrow");
+
+		if (*adaptor == NULL) {
+			/*
+			 * Yarrow doesn't seem to be available.
+			 * Fallback to the first thing that's on the list of
+			 * available RNGs.
+			 */
+			sx_slock(&adaptors_lock);
+
+			rpp = LIST_FIRST(&adaptors);
+			if (rpp != NULL)
+				*adaptor = rpp->rsp;
+
+			sx_sunlock(&adaptors_lock);
+		}
+
+		if (bootverbose && *adaptor)
+			printf("Falling back to <%s> random adaptor",
+			    (*adaptor)->ident);
+	}
+}
+
+static void
+random_proc(void *arg)
+{
+	struct entropy_thread_ctx *ctx;
+	u_char randomness[HARVESTSIZE];
+	int i;
+
+	ctx = (struct entropy_thread_ctx *)arg;
+
+	/* Sanity check. */
+	if (ctx->adaptor == NULL || ctx->adaptor->read == NULL)
+		return;
+
+	for (; *ctx->control == 0;) {
+		i = ctx->adaptor->read(randomness, sizeof(randomness));
+
+		if (i > 0)
+			/* Be very conservative with entropy estimation here. */
+			random_harvest(randomness, i, 0, 0, RANDOM_PURE);
+
+		/* Wake up every 10 secs. */
+		tsleep_sbt(ctx->adaptor, PWAIT | PCATCH, "-", SBT_1M / 6, 0, 0);
+	}
+
+	printf("<%s> entropy source is exiting\n", ctx->adaptor->ident);
+	free(ctx, M_RANDOM_ADAPTORS);
+	kproc_exit(0);
+}
+
+/*
+ * Use RNG's output as an entropy source for another RNG. i.e.:
+ * +--------+          +--------+
+ * | Intel  |          | Yarrow |
+ * | RDRAND +--------->|        |
+ * +--------+          +--------+
+ * Very useful for seeding software RNGs with output of
+ * Hardware RNGs like Intel's RdRand and VIA's Padlock.
+ *
+ * Returns a handle to the newly created kernel process.
+ */
+void *
+random_adaptor_use_as_entropy(const char *id, struct random_adaptor *adaptor,
+    int *control)
+{
+	int error;
+	struct proc *random_chain_proc;
+	struct entropy_thread_ctx *ctx;
+
+	KASSERT(adaptor != NULL, ("can't obtain randomness"));
+	KASSERT(control != NULL, ("can't control entropy process"));
+
+	ctx = malloc(sizeof(struct entropy_thread_ctx), M_RANDOM_ADAPTORS,
+	    M_WAITOK);
+
+	ctx->control = control;
+	ctx->adaptor = adaptor;
+
+	/* Start the thread */
+	error = kproc_create(random_proc, ctx, &random_chain_proc, RFHIGHPID,
+	    0, "%s_entropy", id);
+	if (error != 0)
+		panic("Cannot create rng chaining thread");
+
+	return random_chain_proc;
+}
+
 static void
 random_adaptors_deinit(void *unused)
 {
@@ -99,18 +263,28 @@ static int
 random_sysctl_adaptors_handler(SYSCTL_HANDLER_ARGS)
 {
 	struct random_adaptors	*rpp;
-	int error;
+	int error, count;
 
-	error = 0;
+	count = error = 0;
 
 	sx_slock(&adaptors_lock);
 
-	if (LIST_EMPTY(&adaptors))
-		error = SYSCTL_OUT(req, "", strlen(""));
+	if (LIST_EMPTY(&adaptors)) {
+		error = SYSCTL_OUT(req, "", 0);
+	} else {
+
+		LIST_FOREACH(rpp, &adaptors, entries) {
+
+			error = SYSCTL_OUT(req, ",", count++ ? 1 : 0);
+
+			if (error)
+				break;
+
+			error = SYSCTL_OUT(req, rpp->name, strlen(rpp->name));
 
-	LIST_FOREACH(rpp, &adaptors, entries) {
-		if (0 != SYSCTL_OUT(req, rpp->name, strlen(rpp->name)))
-			break;
+			if (error)
+				break;
+		}
 	}
 
 	sx_sunlock(&adaptors_lock);
@@ -118,6 +292,37 @@ random_sysctl_adaptors_handler(SYSCTL_HANDLER_ARGS)
 	return (error);
 }
 
+static int
+random_sysctl_active_adaptor_handler(SYSCTL_HANDLER_ARGS)
+{
+	struct random_adaptor	*rsp;
+	struct random_adaptors	*rpp;
+	const char		*name;
+	int error;
+
+	name = NULL;
+	rsp = random_get_active_adaptor();
+
+	if (rsp != NULL) {
+		sx_slock(&adaptors_lock);
+
+		LIST_FOREACH(rpp, &adaptors, entries) {
+			if (rpp->rsp == rsp)
+				name = rpp->name;
+		}
+
+		sx_sunlock(&adaptors_lock);
+	}
+
+	if (rsp == NULL || name == NULL) {
+		error = SYSCTL_OUT(req, "", 0);
+	} else {
+		error = SYSCTL_OUT(req, name, strlen(name));
+	}
+
+	return (error);
+}
+
 static void
 random_adaptors_init(void *unused)
 {
@@ -127,6 +332,11 @@ random_adaptors_init(void *unused)
 	    NULL, 0, random_sysctl_adaptors_handler, "",
 	    "Random Number Generator adaptors");
 
+	SYSCTL_PROC(_kern_random, OID_AUTO, active_adaptor,
+	    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
+	    NULL, 0, random_sysctl_active_adaptor_handler, "",
+	    "Active Random Number Generator Adaptor");
+
 	sx_init(&adaptors_lock, "random_adaptors");
 }