2 * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
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.
10 #include <linux/efi.h>
15 struct efi_rng_protocol {
16 efi_status_t (*get_info)(struct efi_rng_protocol *,
17 unsigned long *, efi_guid_t *);
18 efi_status_t (*get_rng)(struct efi_rng_protocol *,
19 efi_guid_t *, unsigned long, u8 *out);
22 efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
23 unsigned long size, u8 *out)
25 efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
27 struct efi_rng_protocol *rng;
29 status = efi_call_early(locate_protocol, &rng_proto, NULL,
31 if (status != EFI_SUCCESS)
34 return rng->get_rng(rng, NULL, size, out);
38 * Return the number of slots covered by this entry, i.e., the number of
39 * addresses it covers that are suitably aligned and supply enough room
42 static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
48 if (md->type != EFI_CONVENTIONAL_MEMORY)
51 start = round_up(md->phys_addr, align);
52 end = round_down(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - size,
58 return (end - start + 1) / align;
62 * The UEFI memory descriptors have a virtual address field that is only used
63 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
64 * is unused here, we can reuse it to keep track of each descriptor's slot
67 #define MD_NUM_SLOTS(md) ((md)->virt_addr)
69 efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
73 unsigned long random_seed)
75 unsigned long map_size, desc_size, total_slots = 0, target_slot;
77 efi_memory_desc_t *memory_map;
80 status = efi_get_memory_map(sys_table_arg, &memory_map, &map_size,
81 &desc_size, NULL, NULL);
82 if (status != EFI_SUCCESS)
85 if (align < EFI_ALLOC_ALIGN)
86 align = EFI_ALLOC_ALIGN;
88 /* count the suitable slots in each memory map entry */
89 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
90 efi_memory_desc_t *md = (void *)memory_map + map_offset;
93 slots = get_entry_num_slots(md, size, align);
94 MD_NUM_SLOTS(md) = slots;
98 /* find a random number between 0 and total_slots */
99 target_slot = (total_slots * (u16)random_seed) >> 16;
102 * target_slot is now a value in the range [0, total_slots), and so
103 * it corresponds with exactly one of the suitable slots we recorded
104 * when iterating over the memory map the first time around.
106 * So iterate over the memory map again, subtracting the number of
107 * slots of each entry at each iteration, until we have found the entry
108 * that covers our chosen slot. Use the residual value of target_slot
109 * to calculate the randomly chosen address, and allocate it directly
110 * using EFI_ALLOCATE_ADDRESS.
112 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
113 efi_memory_desc_t *md = (void *)memory_map + map_offset;
114 efi_physical_addr_t target;
117 if (target_slot >= MD_NUM_SLOTS(md)) {
118 target_slot -= MD_NUM_SLOTS(md);
122 target = round_up(md->phys_addr, align) + target_slot * align;
123 pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
125 status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
126 EFI_LOADER_DATA, pages, &target);
127 if (status == EFI_SUCCESS)
132 efi_call_early(free_pool, memory_map);