cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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arm_smccc_trng.c (2888B)

      1// SPDX-License-Identifier: GPL-2.0
      2/*
      3 * Randomness driver for the ARM SMCCC TRNG Firmware Interface
      4 * https://developer.arm.com/documentation/den0098/latest/
      5 *
      6 *  Copyright (C) 2020 Arm Ltd.
      7 *
      8 * The ARM TRNG firmware interface specifies a protocol to read entropy
      9 * from a higher exception level, to abstract from any machine specific
     10 * implemenations and allow easier use in hypervisors.
     11 *
     12 * The firmware interface is realised using the SMCCC specification.
     13 */
     14
     15#include <linux/bits.h>
     16#include <linux/device.h>
     17#include <linux/hw_random.h>
     18#include <linux/module.h>
     19#include <linux/platform_device.h>
     20#include <linux/arm-smccc.h>
     21
     22#ifdef CONFIG_ARM64
     23#define ARM_SMCCC_TRNG_RND	ARM_SMCCC_TRNG_RND64
     24#define MAX_BITS_PER_CALL	(3 * 64UL)
     25#else
     26#define ARM_SMCCC_TRNG_RND	ARM_SMCCC_TRNG_RND32
     27#define MAX_BITS_PER_CALL	(3 * 32UL)
     28#endif
     29
     30/* We don't want to allow the firmware to stall us forever. */
     31#define SMCCC_TRNG_MAX_TRIES	20
     32
     33#define SMCCC_RET_TRNG_INVALID_PARAMETER	-2
     34#define SMCCC_RET_TRNG_NO_ENTROPY		-3
     35
     36static int copy_from_registers(char *buf, struct arm_smccc_res *res,
     37			       size_t bytes)
     38{
     39	unsigned int chunk, copied;
     40
     41	if (bytes == 0)
     42		return 0;
     43
     44	chunk = min(bytes, sizeof(long));
     45	memcpy(buf, &res->a3, chunk);
     46	copied = chunk;
     47	if (copied >= bytes)
     48		return copied;
     49
     50	chunk = min((bytes - copied), sizeof(long));
     51	memcpy(&buf[copied], &res->a2, chunk);
     52	copied += chunk;
     53	if (copied >= bytes)
     54		return copied;
     55
     56	chunk = min((bytes - copied), sizeof(long));
     57	memcpy(&buf[copied], &res->a1, chunk);
     58
     59	return copied + chunk;
     60}
     61
     62static int smccc_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
     63{
     64	struct arm_smccc_res res;
     65	u8 *buf = data;
     66	unsigned int copied = 0;
     67	int tries = 0;
     68
     69	while (copied < max) {
     70		size_t bits = min_t(size_t, (max - copied) * BITS_PER_BYTE,
     71				  MAX_BITS_PER_CALL);
     72
     73		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND, bits, &res);
     74		if ((int)res.a0 < 0)
     75			return (int)res.a0;
     76
     77		switch ((int)res.a0) {
     78		case SMCCC_RET_SUCCESS:
     79			copied += copy_from_registers(buf + copied, &res,
     80						      bits / BITS_PER_BYTE);
     81			tries = 0;
     82			break;
     83		case SMCCC_RET_TRNG_NO_ENTROPY:
     84			if (!wait)
     85				return copied;
     86			tries++;
     87			if (tries >= SMCCC_TRNG_MAX_TRIES)
     88				return copied;
     89			cond_resched();
     90			break;
     91		}
     92	}
     93
     94	return copied;
     95}
     96
     97static int smccc_trng_probe(struct platform_device *pdev)
     98{
     99	struct hwrng *trng;
    100
    101	trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
    102	if (!trng)
    103		return -ENOMEM;
    104
    105	trng->name = "smccc_trng";
    106	trng->read = smccc_trng_read;
    107
    108	platform_set_drvdata(pdev, trng);
    109
    110	return devm_hwrng_register(&pdev->dev, trng);
    111}
    112
    113static struct platform_driver smccc_trng_driver = {
    114	.driver = {
    115		.name		= "smccc_trng",
    116	},
    117	.probe		= smccc_trng_probe,
    118};
    119module_platform_driver(smccc_trng_driver);
    120
    121MODULE_ALIAS("platform:smccc_trng");
    122MODULE_AUTHOR("Andre Przywara");
    123MODULE_LICENSE("GPL");