sys: Add an SMCCC Random Number Generator driver

The Arm True Random Number Generator Firmware Interface provides a way
to query the SMCCC firmware for up to 192 bits of entropy. Use it to
provide another source of randomness to the kernel.

Reviewed by:	cem, markm
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D46989

sys/conf/files.arm64

@@ -418,6 +418,7 @@ dev/pci/pci_dw_if.m				optional pci fdt
 
 dev/psci/psci.c					standard
 dev/psci/smccc_arm64.S				standard
+dev/psci/smccc_trng.c				standard
 dev/psci/smccc.c				standard
 
 dev/pwm/controller/allwinner/aw_pwm.c		optional fdt aw_pwm

sys/dev/psci/smccc_trng.c

@@ -0,0 +1,143 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2024 Arm Ltd
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * A driver for the Arm True Random Number Generator Firmware Interface.
+ * This queries into the SMCCC firmware for random numbers using the
+ * interface documented in den0098 [1].
+ *
+ * [1] https://developer.arm.com/documentation/den0098/latest
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/bus.h>
+#include <sys/kernel.h>
+#include <sys/malloc.h>
+#include <sys/module.h>
+#include <sys/random.h>
+
+#include <dev/psci/psci.h>
+#include <dev/psci/smccc.h>
+
+#include <dev/random/randomdev.h>
+
+#define	TRNG_VERSION		SMCCC_FUNC_ID(SMCCC_FAST_CALL, \
+    SMCCC_32BIT_CALL, SMCCC_STD_SECURE_SERVICE_CALLS, 0x50)
+#define	 TRNG_VERSION_MIN	0x10000L
+#define	TRNG_RND64		SMCCC_FUNC_ID(SMCCC_FAST_CALL, \
+    SMCCC_64BIT_CALL, SMCCC_STD_SECURE_SERVICE_CALLS, 0x53)
+
+static device_identify_t trng_identify;
+static device_probe_t trng_probe;
+static device_attach_t trng_attach;
+
+static unsigned trng_read(void *, unsigned);
+
+static struct random_source random_trng = {
+	.rs_ident = "Arm SMCCC TRNG",
+	.rs_source = RANDOM_PURE_ARM_TRNG,
+	.rs_read = trng_read,
+};
+
+static void
+trng_identify(driver_t *driver, device_t parent)
+{
+	int32_t version;
+
+	/* TRNG depends on SMCCC 1.1 (per the spec) */
+	if (smccc_get_version() < SMCCC_MAKE_VERSION(1, 1))
+		return;
+
+	/* Check we have TRNG 1.0 or later */
+	version = psci_call(TRNG_VERSION, 0, 0, 0);
+	if (version < TRNG_VERSION_MIN)
+		return;
+
+	if (BUS_ADD_CHILD(parent, 0, "trng", -1) == NULL)
+		device_printf(parent, "add TRNG child failed\n");
+}
+
+static int
+trng_probe(device_t dev)
+{
+	device_set_desc(dev, "Arm SMCCC TRNG");
+	return (BUS_PROBE_NOWILDCARD);
+}
+
+static int
+trng_attach(device_t dev)
+{
+	struct arm_smccc_res res;
+	int32_t ret;
+
+	ret = arm_smccc_invoke(TRNG_RND64, 192, &res);
+	if (ret < 0) {
+		device_printf(dev, "Failed to read fron TRNG\n");
+	} else {
+		random_source_register(&random_trng);
+	}
+
+	return (0);
+}
+
+static unsigned
+trng_read(void *buf, unsigned usz)
+{
+	struct arm_smccc_res res;
+	register_t len;
+	int32_t ret;
+
+	len = usz;
+	if (len > sizeof(uint64_t))
+		len = sizeof(uint64_t);
+	if (len == 0)
+		return (0);
+
+	ret = arm_smccc_invoke(TRNG_RND64, len * 8, &res);
+	if (ret < 0)
+		return (0);
+
+	memcpy(buf, &res.a0, len);
+	return (len);
+}
+
+static device_method_t trng_methods[] = {
+	DEVMETHOD(device_identify,	trng_identify),
+	DEVMETHOD(device_probe,		trng_probe),
+	DEVMETHOD(device_attach,	trng_attach),
+
+	DEVMETHOD_END
+};
+
+static driver_t trng_driver = {
+	"trng",
+	trng_methods,
+	0
+};
+
+DRIVER_MODULE(trng, smccc, trng_driver, 0, 0);

sys/dev/random/random_harvestq.c

@@ -386,6 +386,7 @@ static const char *random_source_descr[ENTROPYSOURCE] = {
 	[RANDOM_PURE_VMGENID] = "PURE_VMGENID",
 	[RANDOM_PURE_QUALCOMM] = "PURE_QUALCOMM",
 	[RANDOM_PURE_ARMV8] = "PURE_ARMV8",
+	[RANDOM_PURE_ARM_TRNG] = "PURE_ARM_TRNG",
 	/* "ENTROPYSOURCE" */
 };
 

sys/sys/random.h

@@ -103,6 +103,7 @@ enum random_entropy_source {
 	RANDOM_PURE_VMGENID,
 	RANDOM_PURE_QUALCOMM,
 	RANDOM_PURE_ARMV8,
+	RANDOM_PURE_ARM_TRNG,
 	ENTROPYSOURCE
 };
 _Static_assert(ENTROPYSOURCE <= 32,