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  */
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  */
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 	efi_rng_protocol_t *rng = NULL;
71 	struct linux_efi_random_seed *seed = NULL;
72 	efi_status_t status;
73 
74 	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
75 	if (status != EFI_SUCCESS)
76 		return status;
77 
78 	/*
79 	 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
80 	 * allocation will survive a kexec reboot (although we refresh the seed
81 	 * beforehand)
82 	 */
83 	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
84 			     sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
85 			     (void **)&seed);
86 	if (status != EFI_SUCCESS)
87 		return status;
88 
89 	status = efi_call_proto(rng, get_rng, &rng_algo_raw,
90 				 EFI_RANDOM_SEED_SIZE, seed->bits);
91 
92 	if (status == EFI_UNSUPPORTED)
93 		/*
94 		 * Use whatever algorithm we have available if the raw algorithm
95 		 * is not implemented.
96 		 */
97 		status = efi_call_proto(rng, get_rng, NULL,
98 					EFI_RANDOM_SEED_SIZE, seed->bits);
99 
100 	if (status != EFI_SUCCESS)
101 		goto err_freepool;
102 
103 	seed->size = EFI_RANDOM_SEED_SIZE;
104 	status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
105 	if (status != EFI_SUCCESS)
106 		goto err_freepool;
107 
108 	return EFI_SUCCESS;
109 
110 err_freepool:
111 	efi_bs_call(free_pool, seed);
112 	return status;
113 }
114