1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
4 */
5
6 #include <linux/efi.h>
7 #include <asm/efi.h>
8
9 #include "efistub.h"
10
11 typedef union efi_rng_protocol efi_rng_protocol_t;
12
13 union efi_rng_protocol {
14 struct {
15 efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *,
16 unsigned long *,
17 efi_guid_t *);
18 efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
19 efi_guid_t *, unsigned long,
20 u8 *out);
21 };
22 struct {
23 u32 get_info;
24 u32 get_rng;
25 } mixed_mode;
26 };
27
28 /**
29 * efi_get_random_bytes() - fill a buffer with random bytes
30 * @size: size of the buffer
31 * @out: caller allocated buffer to receive the random bytes
32 *
33 * The call will fail if either the firmware does not implement the
34 * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill
35 * the buffer.
36 *
37 * Return: status code
38 */
efi_get_random_bytes(unsigned long size,u8 * out)39 efi_status_t efi_get_random_bytes(unsigned long size, u8 *out)
40 {
41 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
42 efi_status_t status;
43 efi_rng_protocol_t *rng = NULL;
44
45 status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
46 if (status != EFI_SUCCESS)
47 return status;
48
49 return efi_call_proto(rng, get_rng, NULL, size, out);
50 }
51
52 /**
53 * efi_random_get_seed() - provide random seed as configuration table
54 *
55 * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are
56 * saved as a configuration table which can be used as entropy by the kernel
57 * for the initialization of its pseudo random number generator.
58 *
59 * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes
60 * available, the configuration table will not be installed and an error code
61 * will be returned.
62 *
63 * Return: status code
64 */
efi_random_get_seed(void)65 efi_status_t efi_random_get_seed(void)
66 {
67 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
68 efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
69 efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
70 struct linux_efi_random_seed *prev_seed, *seed = NULL;
71 int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
72 efi_rng_protocol_t *rng = NULL;
73 efi_status_t status;
74
75 status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
76 if (status != EFI_SUCCESS)
77 return status;
78
79 /*
80 * Check whether a seed was provided by a prior boot stage. In that
81 * case, instead of overwriting it, let's create a new buffer that can
82 * hold both, and concatenate the existing and the new seeds.
83 * Note that we should read the seed size with caution, in case the
84 * table got corrupted in memory somehow.
85 */
86 prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID);
87 if (prev_seed && prev_seed->size <= 512U) {
88 prev_seed_size = prev_seed->size;
89 seed_size += prev_seed_size;
90 }
91
92 /*
93 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
94 * allocation will survive a kexec reboot (although we refresh the seed
95 * beforehand)
96 */
97 status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
98 struct_size(seed, bits, seed_size),
99 (void **)&seed);
100 if (status != EFI_SUCCESS) {
101 efi_warn("Failed to allocate memory for RNG seed.\n");
102 goto err_warn;
103 }
104
105 status = efi_call_proto(rng, get_rng, &rng_algo_raw,
106 EFI_RANDOM_SEED_SIZE, seed->bits);
107
108 if (status == EFI_UNSUPPORTED)
109 /*
110 * Use whatever algorithm we have available if the raw algorithm
111 * is not implemented.
112 */
113 status = efi_call_proto(rng, get_rng, NULL,
114 EFI_RANDOM_SEED_SIZE, seed->bits);
115
116 if (status != EFI_SUCCESS)
117 goto err_freepool;
118
119 seed->size = seed_size;
120 if (prev_seed_size)
121 memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits,
122 prev_seed_size);
123
124 status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
125 if (status != EFI_SUCCESS)
126 goto err_freepool;
127
128 if (prev_seed_size) {
129 /* wipe and free the old seed if we managed to install the new one */
130 memzero_explicit(prev_seed->bits, prev_seed_size);
131 efi_bs_call(free_pool, prev_seed);
132 }
133 return EFI_SUCCESS;
134
135 err_freepool:
136 memzero_explicit(seed, struct_size(seed, bits, seed_size));
137 efi_bs_call(free_pool, seed);
138 efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL\n");
139 err_warn:
140 if (prev_seed)
141 efi_warn("Retaining bootloader-supplied seed only");
142 return status;
143 }
144