random(4): Add is_random_seeded(9) KPI

The imagined use is for early boot consumers of random to be able to make
decisions based on whether random is available yet or not.  One such
consumer seems to be __stack_chk_init(), which runs immediately after random
is initialized.  A follow-up patch will attempt to address that.

Reported by:	many
Reviewed by:	delphij (except man page)
Approved by:	secteam(delphij)
Differential Revision:	https://reviews.freebsd.org/D19926

UPDATING

@@ -31,6 +31,12 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 13.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20190416:
+	The loadable random module KPI has changed; the random_infra_init()
+	routine now requires a 3rd function pointer for a bool (*)(void)
+	method that returns true if the random device is seeded (and
+	therefore unblocked).
+
 20190404:
 	r345895 reverts r320698. This implies that an nfsuserd(8) daemon
 	built from head sources between r320757 (July 6, 2017) and

share/man/man9/Makefile

@@ -1668,6 +1668,7 @@ MLINKS+=psignal.9 gsignal.9 \
 	psignal.9 tdsignal.9
 MLINKS+=random.9 arc4rand.9 \
 	random.9 arc4random.9 \
+	random.9 is_random_seeded.9 \
 	random.9 read_random.9 \
 	random.9 read_random_uio.9 \
 	random.9 srandom.9

share/man/man9/random.9

@@ -26,13 +26,14 @@
 .\"
 .\" $FreeBSD$
 .\" "
-.Dd April 15, 2019
+.Dd April 16, 2019
 .Dt RANDOM 9
 .Os
 .Sh NAME
 .Nm arc4rand ,
 .Nm arc4random ,
 .Nm arc4random_buf ,
+.Nm is_random_seeded ,
 .Nm random ,
 .Nm read_random ,
 .Nm read_random_uio ,
@@ -48,6 +49,8 @@
 .Fn arc4rand "void *ptr" "u_int length" "int reseed"
 .Pp
 .In sys/random.h
+.Ft bool
+.Fn is_random_seeded "void"
 .Ft void
 .Fn read_random "void *buffer" "int count"
 .Ft int
@@ -108,6 +111,13 @@ instead, use the
 family of functions.
 .Pp
 The
+.Fn is_random_seeded
+function can be used to check in advance if
+.Fn read_random
+will block.
+(If random is seeded, it will not block.)
+.Pp
+The
 .Fn read_random_uio
 function behaves identically to
 .Xr read 2

sys/dev/random/random_infra.c

@@ -63,12 +63,20 @@ null_read_random(void *dummy __unused, u_int dummy2 __unused)
 	panic("%s: no random module is loaded", __func__);
 }
 
+static bool
+null_is_random_seeded(void)
+{
+	return (false);
+}
+
 struct random_readers {
 	int	(*read_random_uio)(struct uio *, bool);
 	void	(*read_random)(void *, u_int);
+	bool	(*is_random_seeded)(void);
 } random_reader_context = {
 	(int (*)(struct uio *, bool))nullop,
 	null_read_random,
+	null_is_random_seeded,
 };
 
 struct sx randomdev_config_lock;
@@ -82,12 +90,15 @@ random_infra_sysinit(void *dummy __unused)
 SYSINIT(random_device_h_init, SI_SUB_RANDOM, SI_ORDER_FIRST, random_infra_sysinit, NULL);
 
 void
-random_infra_init(int (*p_random_read_uio)(struct uio *, bool), void (*p_random_read)(void *, u_int))
+random_infra_init(int (*p_random_read_uio)(struct uio *, bool),
+    void (*p_random_read)(void *, u_int),
+    bool (*p_is_random_seeded)(void))
 {
 
 	RANDOM_CONFIG_X_LOCK();
 	random_reader_context.read_random_uio = p_random_read_uio;
 	random_reader_context.read_random = p_random_read;
+	random_reader_context.is_random_seeded = p_is_random_seeded;
 	RANDOM_CONFIG_X_UNLOCK();
 }
 
@@ -98,6 +109,7 @@ random_infra_uninit(void)
 	RANDOM_CONFIG_X_LOCK();
 	random_reader_context.read_random_uio = (int (*)(struct uio *, bool))nullop;
 	random_reader_context.read_random = null_read_random;
+	random_reader_context.is_random_seeded = null_is_random_seeded;
 	RANDOM_CONFIG_X_UNLOCK();
 }
 
@@ -129,4 +141,13 @@ read_random(void *buf, u_int len)
 	RANDOM_CONFIG_S_UNLOCK();
 }
 
+bool
+is_random_seeded(void)
+{
+	RANDOM_CONFIG_S_LOCK();
+	random_reader_context.is_random_seeded();
+	RANDOM_CONFIG_S_UNLOCK();
+}
+
+
 #endif /* defined(RANDOM_LOADABLE) */

sys/dev/random/randomdev.c

@@ -62,11 +62,14 @@ __FBSDID("$FreeBSD$");
 #if defined(RANDOM_LOADABLE)
 #define READ_RANDOM_UIO	_read_random_uio
 #define READ_RANDOM	_read_random
+#define IS_RANDOM_SEEDED	_is_random_seeded
 static int READ_RANDOM_UIO(struct uio *, bool);
 static void READ_RANDOM(void *, u_int);
+static bool IS_RANDOM_SEEDED(void);
 #else
 #define READ_RANDOM_UIO	read_random_uio
 #define READ_RANDOM	read_random
+#define IS_RANDOM_SEEDED	is_random_seeded
 #endif
 
 static d_read_t randomdev_read;
@@ -93,7 +96,7 @@ random_alg_context_ra_init_alg(void *data)
 	p_random_alg_context = &random_alg_context;
 	p_random_alg_context->ra_init_alg(data);
 #if defined(RANDOM_LOADABLE)
-	random_infra_init(READ_RANDOM_UIO, READ_RANDOM);
+	random_infra_init(READ_RANDOM_UIO, READ_RANDOM, IS_RANDOM_SEEDED);
 #endif
 }
 
@@ -271,6 +274,12 @@ READ_RANDOM(void *random_buf, u_int len)
 	}
 }
 
+bool
+IS_RANDOM_SEEDED(void)
+{
+	return (p_random_alg_context->ra_seeded());
+}
+
 static __inline void
 randomdev_accumulate(uint8_t *buf, u_int count)
 {

sys/dev/random/randomdev.h

@@ -118,7 +118,8 @@ extern struct sx randomdev_config_lock;
 #define	RANDOM_CONFIG_S_LOCK(x)		sx_slock(&randomdev_config_lock)
 #define	RANDOM_CONFIG_S_UNLOCK(x)	sx_sunlock(&randomdev_config_lock)
 #define	RANDOM_CONFIG_DEINIT_LOCK(x)	sx_destroy(&randomdev_config_lock)
-void random_infra_init(int (*)(struct uio *, bool), void (*)(void *, u_int));
+void random_infra_init(int (*)(struct uio *, bool), void (*)(void *, u_int),
+    bool (*)(void));
 void random_infra_uninit(void);
 #endif
 

sys/sys/param.h

@@ -60,7 +60,7 @@
  *		in the range 5 to 9.
  */
 #undef __FreeBSD_version
-#define __FreeBSD_version 1300018	/* Master, propagated to newvers */
+#define __FreeBSD_version 1300019	/* Master, propagated to newvers */
 
 /*
  * __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,

sys/sys/random.h

@@ -40,6 +40,7 @@ struct uio;
 #if defined(DEV_RANDOM)
 void read_random(void *, u_int);
 int read_random_uio(struct uio *, bool);
+bool is_random_seeded(void);
 #else
 static __inline int
 read_random_uio(void *a __unused, u_int b __unused)
@@ -50,6 +51,11 @@ static __inline void
 read_random(void *a __unused, u_int b __unused)
 {
 }
+static __inline bool
+is_random_seeded(void)
+{
+	return (false);
+}
 #endif
 
 /*