124 lines
2.8 KiB
C
124 lines
2.8 KiB
C
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// 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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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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default:
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return -EIO;
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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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