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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
75 switch ((int)res.a0) {
76 case SMCCC_RET_SUCCESS:
77 copied += copy_from_registers(buf + copied, &res,
78 bits / BITS_PER_BYTE);
79 tries = 0;
80 break;
81 case SMCCC_RET_TRNG_NO_ENTROPY:
82 if (!wait)
83 return copied;
84 tries++;
85 if (tries >= SMCCC_TRNG_MAX_TRIES)
86 return copied;
87 cond_resched();
88 break;
89 default:
90 return -EIO;
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 return devm_hwrng_register(&pdev->dev, trng);
109}
110
111static struct platform_driver smccc_trng_driver = {
112 .driver = {
113 .name = "smccc_trng",
114 },
115 .probe = smccc_trng_probe,
116};
117module_platform_driver(smccc_trng_driver);
118
119MODULE_ALIAS("platform:smccc_trng");
120MODULE_AUTHOR("Andre Przywara");
121MODULE_LICENSE("GPL");
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
75 switch ((int)res.a0) {
76 case SMCCC_RET_SUCCESS:
77 copied += copy_from_registers(buf + copied, &res,
78 bits / BITS_PER_BYTE);
79 tries = 0;
80 break;
81 case SMCCC_RET_TRNG_NO_ENTROPY:
82 if (!wait)
83 return copied;
84 tries++;
85 if (tries >= SMCCC_TRNG_MAX_TRIES)
86 return copied;
87 cond_resched();
88 break;
89 default:
90 return -EIO;
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");