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