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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
11typedef union efi_rng_protocol efi_rng_protocol_t;
12
13union 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 */
39efi_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 */
65efi_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 unsigned long nv_seed_size = 0, offset = 0;
73 efi_rng_protocol_t *rng = NULL;
74 efi_status_t status;
75
76 status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
77 if (status != EFI_SUCCESS)
78 seed_size = 0;
79
80 // Call GetVariable() with a zero length buffer to obtain the size
81 get_efi_var(L"RandomSeed", &rng_table_guid, NULL, &nv_seed_size, NULL);
82 if (!seed_size && !nv_seed_size)
83 return status;
84
85 seed_size += nv_seed_size;
86
87 /*
88 * Check whether a seed was provided by a prior boot stage. In that
89 * case, instead of overwriting it, let's create a new buffer that can
90 * hold both, and concatenate the existing and the new seeds.
91 * Note that we should read the seed size with caution, in case the
92 * table got corrupted in memory somehow.
93 */
94 prev_seed = get_efi_config_table(rng_table_guid);
95 if (prev_seed && prev_seed->size <= 512U) {
96 prev_seed_size = prev_seed->size;
97 seed_size += prev_seed_size;
98 }
99
100 /*
101 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
102 * allocation will survive a kexec reboot (although we refresh the seed
103 * beforehand)
104 */
105 status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
106 struct_size(seed, bits, seed_size),
107 (void **)&seed);
108 if (status != EFI_SUCCESS) {
109 efi_warn("Failed to allocate memory for RNG seed.\n");
110 goto err_warn;
111 }
112
113 if (rng) {
114 status = efi_call_proto(rng, get_rng, &rng_algo_raw,
115 EFI_RANDOM_SEED_SIZE, seed->bits);
116
117 if (status == EFI_UNSUPPORTED)
118 /*
119 * Use whatever algorithm we have available if the raw algorithm
120 * is not implemented.
121 */
122 status = efi_call_proto(rng, get_rng, NULL,
123 EFI_RANDOM_SEED_SIZE, seed->bits);
124
125 if (status == EFI_SUCCESS)
126 offset = EFI_RANDOM_SEED_SIZE;
127 }
128
129 if (nv_seed_size) {
130 status = get_efi_var(L"RandomSeed", &rng_table_guid, NULL,
131 &nv_seed_size, seed->bits + offset);
132
133 if (status == EFI_SUCCESS)
134 /*
135 * We delete the seed here, and /hope/ that this causes
136 * EFI to also zero out its representation on disk.
137 * This is somewhat idealistic, but overwriting the
138 * variable with zeros is likely just as fraught too.
139 * TODO: in the future, maybe we can hash it forward
140 * instead, and write a new seed.
141 */
142 status = set_efi_var(L"RandomSeed", &rng_table_guid, 0,
143 0, NULL);
144
145 if (status == EFI_SUCCESS)
146 offset += nv_seed_size;
147 else
148 memzero_explicit(seed->bits + offset, nv_seed_size);
149 }
150
151 if (!offset)
152 goto err_freepool;
153
154 if (prev_seed_size) {
155 memcpy(seed->bits + offset, prev_seed->bits, prev_seed_size);
156 offset += prev_seed_size;
157 }
158
159 seed->size = offset;
160 status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
161 if (status != EFI_SUCCESS)
162 goto err_freepool;
163
164 if (prev_seed_size) {
165 /* wipe and free the old seed if we managed to install the new one */
166 memzero_explicit(prev_seed->bits, prev_seed_size);
167 efi_bs_call(free_pool, prev_seed);
168 }
169 return EFI_SUCCESS;
170
171err_freepool:
172 memzero_explicit(seed, struct_size(seed, bits, seed_size));
173 efi_bs_call(free_pool, seed);
174 efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL or EFI variable\n");
175err_warn:
176 if (prev_seed)
177 efi_warn("Retaining bootloader-supplied seed only");
178 return status;
179}
1/*
2 * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
7 *
8 */
9
10#include <linux/efi.h>
11#include <linux/log2.h>
12#include <asm/efi.h>
13
14#include "efistub.h"
15
16struct efi_rng_protocol {
17 efi_status_t (*get_info)(struct efi_rng_protocol *,
18 unsigned long *, efi_guid_t *);
19 efi_status_t (*get_rng)(struct efi_rng_protocol *,
20 efi_guid_t *, unsigned long, u8 *out);
21};
22
23efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
24 unsigned long size, u8 *out)
25{
26 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
27 efi_status_t status;
28 struct efi_rng_protocol *rng;
29
30 status = efi_call_early(locate_protocol, &rng_proto, NULL,
31 (void **)&rng);
32 if (status != EFI_SUCCESS)
33 return status;
34
35 return rng->get_rng(rng, NULL, size, out);
36}
37
38/*
39 * Return the number of slots covered by this entry, i.e., the number of
40 * addresses it covers that are suitably aligned and supply enough room
41 * for the allocation.
42 */
43static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
44 unsigned long size,
45 unsigned long align_shift)
46{
47 unsigned long align = 1UL << align_shift;
48 u64 first_slot, last_slot, region_end;
49
50 if (md->type != EFI_CONVENTIONAL_MEMORY)
51 return 0;
52
53 region_end = min((u64)ULONG_MAX, md->phys_addr + md->num_pages*EFI_PAGE_SIZE - 1);
54
55 first_slot = round_up(md->phys_addr, align);
56 last_slot = round_down(region_end - size + 1, align);
57
58 if (first_slot > last_slot)
59 return 0;
60
61 return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
62}
63
64/*
65 * The UEFI memory descriptors have a virtual address field that is only used
66 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
67 * is unused here, we can reuse it to keep track of each descriptor's slot
68 * count.
69 */
70#define MD_NUM_SLOTS(md) ((md)->virt_addr)
71
72efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
73 unsigned long size,
74 unsigned long align,
75 unsigned long *addr,
76 unsigned long random_seed)
77{
78 unsigned long map_size, desc_size, total_slots = 0, target_slot;
79 unsigned long buff_size;
80 efi_status_t status;
81 efi_memory_desc_t *memory_map;
82 int map_offset;
83 struct efi_boot_memmap map;
84
85 map.map = &memory_map;
86 map.map_size = &map_size;
87 map.desc_size = &desc_size;
88 map.desc_ver = NULL;
89 map.key_ptr = NULL;
90 map.buff_size = &buff_size;
91
92 status = efi_get_memory_map(sys_table_arg, &map);
93 if (status != EFI_SUCCESS)
94 return status;
95
96 if (align < EFI_ALLOC_ALIGN)
97 align = EFI_ALLOC_ALIGN;
98
99 /* count the suitable slots in each memory map entry */
100 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
101 efi_memory_desc_t *md = (void *)memory_map + map_offset;
102 unsigned long slots;
103
104 slots = get_entry_num_slots(md, size, ilog2(align));
105 MD_NUM_SLOTS(md) = slots;
106 total_slots += slots;
107 }
108
109 /* find a random number between 0 and total_slots */
110 target_slot = (total_slots * (u16)random_seed) >> 16;
111
112 /*
113 * target_slot is now a value in the range [0, total_slots), and so
114 * it corresponds with exactly one of the suitable slots we recorded
115 * when iterating over the memory map the first time around.
116 *
117 * So iterate over the memory map again, subtracting the number of
118 * slots of each entry at each iteration, until we have found the entry
119 * that covers our chosen slot. Use the residual value of target_slot
120 * to calculate the randomly chosen address, and allocate it directly
121 * using EFI_ALLOCATE_ADDRESS.
122 */
123 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
124 efi_memory_desc_t *md = (void *)memory_map + map_offset;
125 efi_physical_addr_t target;
126 unsigned long pages;
127
128 if (target_slot >= MD_NUM_SLOTS(md)) {
129 target_slot -= MD_NUM_SLOTS(md);
130 continue;
131 }
132
133 target = round_up(md->phys_addr, align) + target_slot * align;
134 pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
135
136 status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
137 EFI_LOADER_DATA, pages, &target);
138 if (status == EFI_SUCCESS)
139 *addr = target;
140 break;
141 }
142
143 efi_call_early(free_pool, memory_map);
144
145 return status;
146}
147
148efi_status_t efi_random_get_seed(efi_system_table_t *sys_table_arg)
149{
150 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
151 efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
152 efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
153 struct efi_rng_protocol *rng;
154 struct linux_efi_random_seed *seed;
155 efi_status_t status;
156
157 status = efi_call_early(locate_protocol, &rng_proto, NULL,
158 (void **)&rng);
159 if (status != EFI_SUCCESS)
160 return status;
161
162 status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
163 sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
164 (void **)&seed);
165 if (status != EFI_SUCCESS)
166 return status;
167
168 status = rng->get_rng(rng, &rng_algo_raw, EFI_RANDOM_SEED_SIZE,
169 seed->bits);
170 if (status == EFI_UNSUPPORTED)
171 /*
172 * Use whatever algorithm we have available if the raw algorithm
173 * is not implemented.
174 */
175 status = rng->get_rng(rng, NULL, EFI_RANDOM_SEED_SIZE,
176 seed->bits);
177
178 if (status != EFI_SUCCESS)
179 goto err_freepool;
180
181 seed->size = EFI_RANDOM_SEED_SIZE;
182 status = efi_call_early(install_configuration_table, &rng_table_guid,
183 seed);
184 if (status != EFI_SUCCESS)
185 goto err_freepool;
186
187 return EFI_SUCCESS;
188
189err_freepool:
190 efi_call_early(free_pool, seed);
191 return status;
192}