* [PATCH v3 1/2] firmware: smccc: Register smccc_trng platform device
2021-07-26 17:56 [PATCH v3 0/2] hwrng: Add Arm SMCCC TRNG based driver Andre Przywara
@ 2021-07-26 17:56 ` Andre Przywara
2021-07-26 17:56 ` [PATCH v3 2/2] hwrng: Add Arm SMCCC TRNG based driver Andre Przywara
1 sibling, 0 replies; 6+ messages in thread
From: Andre Przywara @ 2021-07-26 17:56 UTC (permalink / raw)
To: Matt Mackall, Herbert Xu, Mark Rutland, Lorenzo Pieralisi, Sudeep Holla
Cc: linux-crypto, linux-arm-kernel, linux-kernel,
Benjamin Herrenschmidt, Ard Biesheuvel, Mark Brown, Will Deacon,
Ali Saidi, Jon Nettleton
At the moment we probe for the Random Number Generator SMCCC service,
and use that in the core code (arch_get_random). However the hardware
entropy can also be useful to access from userland, and be it to assess
its quality.
Register a platform device when the SMCCC TRNG service is detected, to
allow a hw_random driver to hook onto this.
The function registering the device is deliberately made in a way which
allows expansion, so other services that could be exposed via a platform
device (or some other interface), can be added here easily.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
drivers/firmware/smccc/smccc.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
index 9f937b125ab0..60ccf3e90d7d 100644
--- a/drivers/firmware/smccc/smccc.c
+++ b/drivers/firmware/smccc/smccc.c
@@ -9,6 +9,7 @@
#include <linux/init.h>
#include <linux/arm-smccc.h>
#include <linux/kernel.h>
+#include <linux/platform_device.h>
#include <asm/archrandom.h>
static u32 smccc_version = ARM_SMCCC_VERSION_1_0;
@@ -42,3 +43,19 @@ u32 arm_smccc_get_version(void)
return smccc_version;
}
EXPORT_SYMBOL_GPL(arm_smccc_get_version);
+
+static int __init smccc_devices_init(void)
+{
+ struct platform_device *pdev;
+
+ if (smccc_trng_available) {
+ pdev = platform_device_register_simple("smccc_trng", -1,
+ NULL, 0);
+ if (IS_ERR(pdev))
+ pr_err("smccc_trng: could not register device: %ld\n",
+ PTR_ERR(pdev));
+ }
+
+ return 0;
+}
+device_initcall(smccc_devices_init);
--
2.17.6
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH v3 2/2] hwrng: Add Arm SMCCC TRNG based driver
2021-07-26 17:56 [PATCH v3 0/2] hwrng: Add Arm SMCCC TRNG based driver Andre Przywara
2021-07-26 17:56 ` [PATCH v3 1/2] firmware: smccc: Register smccc_trng platform device Andre Przywara
@ 2021-07-26 17:56 ` Andre Przywara
2021-07-26 22:37 ` Mark Brown
1 sibling, 1 reply; 6+ messages in thread
From: Andre Przywara @ 2021-07-26 17:56 UTC (permalink / raw)
To: Matt Mackall, Herbert Xu, Mark Rutland, Lorenzo Pieralisi, Sudeep Holla
Cc: linux-crypto, linux-arm-kernel, linux-kernel,
Benjamin Herrenschmidt, Ard Biesheuvel, Mark Brown, Will Deacon,
Ali Saidi, Jon Nettleton
The "Arm True Random Number Generator Firmware Interface"[1] provides
an SMCCC based interface to a true hardware random number generator.
So far we are using that in arch_get_random_seed(), but it might be
useful to expose the entropy through the /dev/hwrng device as well. This
allows to assess the quality of the implementation, by using "rngtest"
from the rng-tools package, for example.
Add a simple platform driver implementing the hw_random interface.
The corresponding platform device is created by the SMCCC core code,
we just match it here by name and provide a module alias.
Since the firmware takes care about serialisation, this can happily
coexist with the arch_get_random_seed() bits.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[1] https://developer.arm.com/documentation/den0098/latest/
---
drivers/char/hw_random/Kconfig | 14 +++
drivers/char/hw_random/Makefile | 1 +
drivers/char/hw_random/arm_smccc_trng.c | 134 ++++++++++++++++++++++++
3 files changed, 149 insertions(+)
create mode 100644 drivers/char/hw_random/arm_smccc_trng.c
diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index 3f166c8a4099..239eca4d6805 100644
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -524,6 +524,20 @@ config HW_RANDOM_XIPHERA
To compile this driver as a module, choose M here: the
module will be called xiphera-trng.
+config HW_RANDOM_ARM_SMCCC_TRNG
+ tristate "Arm SMCCC TRNG firmware interface support"
+ depends on HAVE_ARM_SMCCC_DISCOVERY
+ default HW_RANDOM
+ help
+ Say 'Y' to enable the True Random Number Generator driver using
+ the Arm SMCCC TRNG firmware interface. This reads entropy from
+ higher exception levels (firmware, hypervisor). Uses SMCCC for
+ communicating with the firmware:
+ https://developer.arm.com/documentation/den0098/latest/
+
+ To compile this driver as a module, choose M here: the
+ module will be called arm_smccc_trng.
+
endif # HW_RANDOM
config UML_RANDOM
diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
index 8933fada74f2..a5a1c765a394 100644
--- a/drivers/char/hw_random/Makefile
+++ b/drivers/char/hw_random/Makefile
@@ -45,3 +45,4 @@ obj-$(CONFIG_HW_RANDOM_OPTEE) += optee-rng.o
obj-$(CONFIG_HW_RANDOM_NPCM) += npcm-rng.o
obj-$(CONFIG_HW_RANDOM_CCTRNG) += cctrng.o
obj-$(CONFIG_HW_RANDOM_XIPHERA) += xiphera-trng.o
+obj-$(CONFIG_HW_RANDOM_ARM_SMCCC_TRNG) += arm_smccc_trng.o
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 000000000000..a04f9f9db1fe
--- /dev/null
+++ b/drivers/char/hw_random/arm_smccc_trng.c
@@ -0,0 +1,134 @@
+// 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 smccc_trng_init(struct hwrng *rng)
+{
+ return 0;
+}
+
+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);
+ if ((int)res.a0 < 0)
+ return (int)res.a0;
+
+ 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;
+ }
+ }
+
+ return copied;
+}
+
+static int smccc_trng_probe(struct platform_device *pdev)
+{
+ struct hwrng *trng;
+ int ret;
+
+ trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
+ if (!trng)
+ return -ENOMEM;
+
+ trng->name = "smccc_trng";
+ trng->init = smccc_trng_init;
+ trng->read = smccc_trng_read;
+
+ platform_set_drvdata(pdev, trng);
+ ret = devm_hwrng_register(&pdev->dev, trng);
+ if (!ret)
+ dev_info(&pdev->dev,
+ "ARM SMCCC TRNG firmware random number generator\n");
+
+ return ret;
+}
+
+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");
--
2.17.6
^ permalink raw reply [flat|nested] 6+ messages in thread