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author | Andre Przywara <andre.przywara@arm.com> | 2021-07-31 21:48:45 +0100 |
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committer | Herbert Xu <herbert@gondor.apana.org.au> | 2021-08-06 19:45:26 +0800 |
commit | 0888d04b47a165ae8c429c6fe11b3c43f5017f31 (patch) | |
tree | fb948c4e44df2655c671fa600b17476389bb7d50 /drivers/char | |
parent | b83c2d92be719bf7b1d24ac02aaa53db3991ea58 (diff) | |
download | linux-0888d04b47a165ae8c429c6fe11b3c43f5017f31.tar.bz2 |
hwrng: Add Arm SMCCC TRNG based driver
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.
[1] https://developer.arm.com/documentation/den0098/latest/
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'drivers/char')
-rw-r--r-- | drivers/char/hw_random/Kconfig | 14 | ||||
-rw-r--r-- | drivers/char/hw_random/Makefile | 1 | ||||
-rw-r--r-- | drivers/char/hw_random/arm_smccc_trng.c | 123 |
3 files changed, 138 insertions, 0 deletions
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..b24ac39a903b --- /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); + 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; + + 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"); |