1 files changed, 123 insertions, 0 deletions
diff --git a/drivers/char/hw_random/arm_smccc_trng.c b/drivers/char/hw_random/arm_smccc_trng.c
new file mode 100644
index 000000000..e34c3ea69
--- /dev/null
+++ b/drivers/char/hw_random/arm_smccc_trng.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Randomness driver for the ARM SMCCC TRNG Firmware Interface
+ * https://developer.arm.com/documentation/den0098/latest/
+ *
+ *  Copyright (C) 2020 Arm Ltd.
+ *
+ * The ARM TRNG firmware interface specifies a protocol to read entropy
+ * from a higher exception level, to abstract from any machine specific
+ * implemenations and allow easier use in hypervisors.
+ *
+ * The firmware interface is realised using the SMCCC specification.
+ */
+
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/hw_random.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/arm-smccc.h>
+
+#ifdef CONFIG_ARM64
+#define ARM_SMCCC_TRNG_RND	ARM_SMCCC_TRNG_RND64
+#define MAX_BITS_PER_CALL	(3 * 64UL)
+#else
+#define ARM_SMCCC_TRNG_RND	ARM_SMCCC_TRNG_RND32
+#define MAX_BITS_PER_CALL	(3 * 32UL)
+#endif
+
+/* We don't want to allow the firmware to stall us forever. */
+#define SMCCC_TRNG_MAX_TRIES	20
+
+#define SMCCC_RET_TRNG_INVALID_PARAMETER	-2
+#define SMCCC_RET_TRNG_NO_ENTROPY		-3
+
+static int copy_from_registers(char *buf, struct arm_smccc_res *res,
+			       size_t bytes)
+{
+	unsigned int chunk, copied;
+
+	if (bytes == 0)
+		return 0;
+
+	chunk = min(bytes, sizeof(long));
+	memcpy(buf, &res->a3, chunk);
+	copied = chunk;
+	if (copied >= bytes)
+		return copied;
+
+	chunk = min((bytes - copied), sizeof(long));
+	memcpy(&buf[copied], &res->a2, chunk);
+	copied += chunk;
+	if (copied >= bytes)
+		return copied;
+
+	chunk = min((bytes - copied), sizeof(long));
+	memcpy(&buf[copied], &res->a1, chunk);
+
+	return copied + chunk;
+}
+
+static int smccc_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+	struct arm_smccc_res res;
+	u8 *buf = data;
+	unsigned int copied = 0;
+	int tries = 0;
+
+	while (copied < max) {
+		size_t bits = min_t(size_t, (max - copied) * BITS_PER_BYTE,
+				  MAX_BITS_PER_CALL);
+
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND, bits, &res);
+
+		switch ((int)res.a0) {
+		case SMCCC_RET_SUCCESS:
+			copied += copy_from_registers(buf + copied, &res,
+						      bits / BITS_PER_BYTE);
+			tries = 0;
+			break;
+		case SMCCC_RET_TRNG_NO_ENTROPY:
+			if (!wait)
+				return copied;
+			tries++;
+			if (tries >= SMCCC_TRNG_MAX_TRIES)
+				return copied;
+			cond_resched();
+			break;
+		default:
+			return -EIO;
+		}
+	}
+
+	return copied;
+}
+
+static int smccc_trng_probe(struct platform_device *pdev)
+{
+	struct hwrng *trng;
+
+	trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
+	if (!trng)
+		return -ENOMEM;
+
+	trng->name = "smccc_trng";
+	trng->read = smccc_trng_read;
+
+	platform_set_drvdata(pdev, trng);
+
+	return devm_hwrng_register(&pdev->dev, trng);
+}
+
+static struct platform_driver smccc_trng_driver = {
+	.driver = {
+		.name		= "smccc_trng",
+	},
+	.probe		= smccc_trng_probe,
+};
+module_platform_driver(smccc_trng_driver);
+
+MODULE_ALIAS("platform:smccc_trng");
+MODULE_AUTHOR("Andre Przywara");
+MODULE_LICENSE("GPL");