[PATCH REVIEW] hwrng: add exynos Secure World RNG device driver

[Alexey Klimov]

The Exynos TRNG device is controlled by firmware and shared between
non-secure world and secure world. Access to it is exposed via SMC
interface which is implemented here. The firmware code does
additional security checks, start-up test and some checks on resume.

This device is found, for instance, in Google Tensor GS101-family
of devices.

Signed-off-by: Alexey Klimov <alexey.klimov@xxxxxxxxxx>
---
 drivers/char/hw_random/Kconfig           |  12 +
 drivers/char/hw_random/Makefile          |   1 +
 drivers/char/hw_random/exynos-swd-trng.c | 423 +++++++++++++++++++++++
 3 files changed, 436 insertions(+)
 create mode 100644 drivers/char/hw_random/exynos-swd-trng.c

diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index 442c40efb200..bff7c3ec129a 100644
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -479,6 +479,18 @@ config HW_RANDOM_EXYNOS
 
 	  If unsure, say Y.
 
+config HW_RANDOM_EXYNOS_SWD
+	tristate "Exynos SWD HW random number generator support"
+	default n
+	help
+	  This driver provides kernel-side support for accessing Samsung
+	  TRNG hardware located in secure world using smc calls.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called exynos-swd-trng.
+
+	  If unsure, say N.
+
 config HW_RANDOM_OPTEE
 	tristate "OP-TEE based Random Number Generator support"
 	depends on OPTEE
diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
index 32549a1186dc..ce64929d461a 100644
--- a/drivers/char/hw_random/Makefile
+++ b/drivers/char/hw_random/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_HW_RANDOM_N2RNG) += n2-rng.o
 n2-rng-y := n2-drv.o n2-asm.o
 obj-$(CONFIG_HW_RANDOM_VIA) += via-rng.o
 obj-$(CONFIG_HW_RANDOM_EXYNOS) += exynos-trng.o
+obj-$(CONFIG_HW_RANDOM_EXYNOS_SWD) += exynos-swd-trng.o
 obj-$(CONFIG_HW_RANDOM_IXP4XX) += ixp4xx-rng.o
 obj-$(CONFIG_HW_RANDOM_OMAP) += omap-rng.o
 obj-$(CONFIG_HW_RANDOM_OMAP3_ROM) += omap3-rom-rng.o
diff --git a/drivers/char/hw_random/exynos-swd-trng.c b/drivers/char/hw_random/exynos-swd-trng.c
new file mode 100644
index 000000000000..29def8e6d0b7
--- /dev/null
+++ b/drivers/char/hw_random/exynos-swd-trng.c
@@ -0,0 +1,423 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * exynos-swd-trng.c - Random Number Generator driver for the exynos TRNG
+ * located in secure world
+ * Copyright (C) Linaro Ltd 2024 Alexey Klimov <alexey.klimov@xxxxxxxxxx>
+ *
+ * Based on downstream driver:
+ * Copyright (C) 2018 Samsung Electronics
+ * Sehee Kim <sehi.kim@xxxxxxxxxxx>
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/delay.h>
+#include <linux/hw_random.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/platform_device.h>
+#include <linux/pm_runtime.h>
+
+/* DTRNG smc */
+#define SMC_CMD_RANDOM			(0x82001012)
+
+/* DTRNG smc commands */
+#define HWRNG_INIT			(0x0)
+#define HWRNG_EXIT			(0x1)
+#define HWRNG_GET_DATA			(0x2)
+#define HWRNG_RESUME			(0x3)
+
+#define HWRNG_RET_OK			0
+#define HWRNG_RET_INVALID_ERROR		1
+#define HWRNG_RET_RETRY_ERROR		2
+#define HWRNG_RET_INVALID_FLAG_ERROR	3
+#define HWRNG_RET_TEST_ERROR		4
+#define HWRNG_RET_START_UP_TEST_DONE	5
+#define HWRNG_RET_TEST_KAT_ERROR	0xC
+
+#define EXYRNG_START_UP_SIZE		(4096 + 1)
+#define EXYRNG_RETRY_MAX_COUNT		1000000
+#define EXYRNG_START_UP_TEST_MAX_RETRY	2
+
+#define DRVNAME	"exynos_swd_trng"
+
+enum state {
+	INACTIVE = 0,
+	ACTIVE,
+};
+
+struct exyswd_rng {
+	struct hwrng rng;
+	enum state state;
+	struct device *dev;
+	/* to track and protect state of the device */
+	struct mutex lock;
+};
+
+static int __exynos_cm_smc(u64 *arg0, u64 *arg1,
+			   u64 *arg2, u64 *arg3)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_smc(*arg0, *arg1, *arg2, *arg3, 0, 0, 0, 0, &res);
+
+	*arg0 = res.a0;
+	*arg1 = res.a1;
+	*arg2 = res.a2;
+	*arg3 = res.a3;
+
+	return *arg0;
+}
+
+static int exynos_cm_cmd(int cmd)
+{
+	u64 reg0, reg1, reg2, reg3;
+
+	reg0 = SMC_CMD_RANDOM;
+	reg1 = cmd;
+	reg3 = reg2 = 0;
+
+	return __exynos_cm_smc(&reg0, &reg1, &reg2, &reg3);
+}
+
+static int exynos_cm_get_data(u64 *arg0, u64 *arg1,
+			      u64 *arg2, u64 *arg3)
+{
+	*arg0 = SMC_CMD_RANDOM;
+	*arg1 = HWRNG_GET_DATA;
+	*arg3 = 0;
+
+	return __exynos_cm_smc(arg0, arg1, arg2, arg3);
+}
+
+static int exynos_swd_get_data(u64 *arg0, u64 *arg1, u64 *arg2, u64 *arg3,
+			       struct exyswd_rng *exyswd_rng)
+{
+	u32 retry_cnt = 0;
+	int ret;
+
+	while (retry_cnt++ < EXYRNG_RETRY_MAX_COUNT) {
+		ret = exynos_cm_get_data(arg0, arg1, arg2, arg3);
+
+		if (ret == HWRNG_RET_OK)
+			return 0;
+
+		if (ret == HWRNG_RET_RETRY_ERROR) {
+			usleep_range(50, 100);
+			continue;
+		}
+
+		if (ret == HWRNG_RET_TEST_ERROR) {
+			dev_dbg(exyswd_rng->dev, "error while testing\n");
+			return -EAGAIN;
+		}
+
+		return -EFAULT;
+	}
+
+	ret = -EFAULT;
+	dev_warn(exyswd_rng->dev, "retry counter is reached\n");
+	return ret;
+}
+
+static int exynos_swd_init(void)
+{
+	u32 retry_cnt = 0;
+	int ret;
+
+	do {
+		ret = exynos_cm_cmd(HWRNG_INIT);
+		if (ret == HWRNG_RET_RETRY_ERROR) {
+			if (retry_cnt++ > EXYRNG_RETRY_MAX_COUNT)
+				break;
+
+			usleep_range(50, 100);
+		}
+	} while (ret == HWRNG_RET_RETRY_ERROR);
+
+	return ret;
+}
+
+static void exynos_swd_exit(void)
+{
+	u32 retry_cnt = 0;
+
+	while (retry_cnt++ < EXYRNG_RETRY_MAX_COUNT) {
+		if (!exynos_cm_cmd(HWRNG_EXIT))
+			break;
+		usleep_range(50, 100);
+	}
+}
+
+static int exynos_swd_startup_test(struct exyswd_rng *exyswd_rng)
+{
+	u64 reg0, reg1, reg2, reg3;
+	int start_up_size = EXYRNG_START_UP_SIZE;
+	u32 retry_cnt = 0;
+	int ret;
+
+	ret = exynos_swd_init();
+	if (ret != HWRNG_RET_OK) {
+		if (ret == HWRNG_RET_TEST_ERROR) {
+			ret = -EAGAIN;
+			goto out;
+		} else
+			return -EFAULT;
+	}
+
+	while (start_up_size > 0) {
+		/* For start-up test the 3-rd argument has to be set to 1 */
+		reg2 = 1;
+		ret = exynos_cm_get_data(&reg0, &reg1, &reg2, &reg3);
+		if (ret == HWRNG_RET_RETRY_ERROR) {
+			if (retry_cnt++ > EXYRNG_RETRY_MAX_COUNT) {
+				dev_warn(exyswd_rng->dev,
+					 "exceeded retry in start-up test\n");
+				break;
+			}
+			usleep_range(50, 100);
+			continue;
+		}
+
+		if (ret == HWRNG_RET_TEST_ERROR ||
+		    ret == HWRNG_RET_TEST_KAT_ERROR) {
+			dev_err(exyswd_rng->dev,
+				"malfunction of TRNG(HW) is detected\n");
+			return -EFAULT;
+		}
+
+		if (ret == HWRNG_RET_START_UP_TEST_DONE) {
+			dev_dbg(exyswd_rng->dev,
+				"start-up test is already done\n");
+			ret = 0;
+			break;
+		}
+
+		if (ret != HWRNG_RET_OK) {
+			dev_dbg(exyswd_rng->dev, "failed to get random data\n");
+			return -EFAULT;
+		}
+
+		start_up_size -= 32;
+		retry_cnt = 0;
+	}
+
+out:
+	exynos_swd_exit();
+	return ret;
+}
+
+static int exynos_swd_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+	struct exyswd_rng *exyswd_rng =
+				container_of(rng, struct exyswd_rng, rng);
+	u64 reg0, reg1, reg2, reg3;
+	u32 *read_buf = data;
+	u32 read_size = max;
+	u32 retry_cnt;
+	int ret = HWRNG_RET_OK;
+
+	mutex_lock(&exyswd_rng->lock);
+	ret = exynos_swd_init();
+	if (ret != HWRNG_RET_OK) {
+		if (ret == HWRNG_RET_TEST_ERROR) {
+			ret = -EAGAIN;
+			goto out_locked;
+		} else {
+			mutex_unlock(&exyswd_rng->lock);
+			return -EFAULT;
+		}
+	}
+
+	exyswd_rng->state = ACTIVE;
+	mutex_unlock(&exyswd_rng->lock);
+
+	retry_cnt = 0;
+	while (read_size >= 8) {
+		reg2 = 0;
+		ret = exynos_swd_get_data(&reg0, &reg1, &reg2, &reg3, exyswd_rng);
+		if (ret)
+			goto out;
+
+		*(u32 *)(read_buf++) = (u32)reg2;
+		*(u32 *)(read_buf++) = (u32)reg3;
+
+		read_size -= 8;
+		retry_cnt = 0;
+	}
+
+	/*
+	 * rng_buf_size is 32 bytes or cache line usually, it is unlikely
+	 * we will have remaining bytes to read here.
+	 */
+	if (unlikely(read_size > 0)) {
+		reg2 = 0;
+		ret = exynos_swd_get_data(&reg0, &reg1, &reg2, &reg3, exyswd_rng);
+		if (ret)
+			goto out;
+		if (read_size >= 4) {
+			*(u32 *)(read_buf++) = (u32)reg2;
+			read_size -= 4;
+		}
+
+		if (read_size) {
+			memcpy(read_buf, &reg3, read_size);
+			read_size = 0;
+		}
+	}
+
+	ret = max;
+out:
+	mutex_lock(&exyswd_rng->lock);
+out_locked:
+	exynos_swd_exit();
+	exyswd_rng->state = INACTIVE;
+	mutex_unlock(&exyswd_rng->lock);
+
+	return ret;
+}
+
+static int exyswd_rng_probe(struct platform_device *pdev)
+{
+	struct exyswd_rng *exyswd_rng;
+	int ret;
+
+	exyswd_rng = devm_kzalloc(&pdev->dev, sizeof(*exyswd_rng), GFP_KERNEL);
+	if (!exyswd_rng)
+		return -ENOMEM;
+
+	exyswd_rng->rng.name = DRVNAME;
+	exyswd_rng->rng.read = exynos_swd_read;
+	exyswd_rng->rng.quality = 500;
+	exyswd_rng->dev = &pdev->dev;
+	exyswd_rng->state = INACTIVE;
+	mutex_init(&exyswd_rng->lock);
+
+	/*
+	 * Do the startup test first. If it works we've got the device
+	 * and can finish probe().
+	 */
+	ret = exynos_swd_startup_test(exyswd_rng);
+	if (ret) {
+		dev_dbg(&pdev->dev, "start-up test failed\n");
+		return -ENODEV;
+	}
+
+	ret = devm_hwrng_register(&pdev->dev, &exyswd_rng->rng);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "failed to register hwrng\n");
+
+	platform_set_drvdata(pdev, exyswd_rng);
+	dev_set_drvdata(&pdev->dev, exyswd_rng);
+
+	dev_info(&pdev->dev, "hwrng registered\n");
+
+	return 0;
+}
+
+static int exyswd_rng_remove(struct platform_device *pdev)
+{
+	struct exyswd_rng *exyswd_rng = platform_get_drvdata(pdev);
+
+	devm_hwrng_unregister(&pdev->dev, &exyswd_rng->rng);
+
+	mutex_lock(&exyswd_rng->lock);
+	if (exyswd_rng->state == ACTIVE) {
+		exynos_swd_exit();
+		exyswd_rng->state = INACTIVE;
+	}
+	mutex_unlock(&exyswd_rng->lock);
+
+	return 0;
+}
+
+#if defined(CONFIG_PM_SLEEP) || defined(CONFIG_PM_RUNTIME)
+static int exyswd_rng_suspend(struct device *dev)
+{
+	struct exyswd_rng *exyswd_rng = dev_get_drvdata(dev);
+	int ret = 0;
+
+	mutex_lock(&exyswd_rng->lock);
+	if (exyswd_rng->state) {
+		ret = exynos_cm_cmd(HWRNG_EXIT);
+		if (ret != HWRNG_RET_OK)
+			dev_warn(dev,
+				 "failed to enter suspend, error %d\n", ret);
+	}
+	mutex_unlock(&exyswd_rng->lock);
+
+	return ret;
+}
+
+static int exyswd_rng_resume(struct device *dev)
+{
+	struct exyswd_rng *exyswd_rng = dev_get_drvdata(dev);
+	int ret;
+
+	mutex_lock(&exyswd_rng->lock);
+	ret = exynos_cm_cmd(HWRNG_RESUME);
+	if (ret != HWRNG_RET_OK)
+		dev_warn(dev, "failed to resume, error %d\n", ret);
+	if (exyswd_rng->state) {
+		ret = exynos_cm_cmd(HWRNG_INIT);
+		if (ret != HWRNG_RET_OK)
+			dev_warn(dev,
+				 "failed to init hwrng on resume, error %d\n",
+				 ret);
+	}
+	mutex_unlock(&exyswd_rng->lock);
+
+	return ret;
+}
+#endif
+
+static UNIVERSAL_DEV_PM_OPS(exyswd_rng_pm_ops, exyswd_rng_suspend,
+			    exyswd_rng_resume, NULL);
+
+static struct platform_driver exyswd_rng_driver = {
+	.probe		= exyswd_rng_probe,
+	.remove		= exyswd_rng_remove,
+	.driver		= {
+		.name	= DRVNAME,
+		.owner	= THIS_MODULE,
+		.pm     = &exyswd_rng_pm_ops,
+	},
+};
+
+static struct platform_device *exyswd_rng_pdev;
+
+static int __init exyswd_rng_init(void)
+{
+	int ret;
+
+	exyswd_rng_pdev = platform_device_register_simple(DRVNAME, -1, NULL, 0);
+	if (IS_ERR(exyswd_rng_pdev))
+		pr_err(DRVNAME ": could not register device: %ld\n",
+		       PTR_ERR(exyswd_rng_pdev));
+
+	ret = platform_driver_register(&exyswd_rng_driver);
+	if (ret) {
+		platform_device_unregister(exyswd_rng_pdev);
+		return ret;
+	}
+
+	pr_info("ExyRNG driver, (c) 2014 Samsung Electronics\n");
+
+	return 0;
+}
+
+static void __exit exyswd_rng_exit(void)
+{
+	platform_driver_unregister(&exyswd_rng_driver);
+	platform_device_unregister(exyswd_rng_pdev);
+}
+
+module_init(exyswd_rng_init);
+module_exit(exyswd_rng_exit);
+
+MODULE_DESCRIPTION("Exynos SWD H/W Random Number Generator driver");
+MODULE_AUTHOR("Alexey Klimov <alexey.klimov@xxxxxxxxxx>");
+MODULE_AUTHOR("Sehee Kim <sehi.kim@xxxxxxxxxxx>");
+MODULE_LICENSE("GPL");
-- 
2.43.0