1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
7 #include <linux/log2.h>
13 * Return the number of slots covered by this entry, i.e., the number of
14 * addresses it covers that are suitably aligned and supply enough room
17 static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
19 unsigned long align_shift)
21 unsigned long align = 1UL << align_shift;
22 u64 first_slot, last_slot, region_end;
24 if (md->type != EFI_CONVENTIONAL_MEMORY)
27 if (efi_soft_reserve_enabled() &&
28 (md->attribute & EFI_MEMORY_SP))
31 region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
33 if (region_end < size)
36 first_slot = round_up(md->phys_addr, align);
37 last_slot = round_down(region_end - size + 1, align);
39 if (first_slot > last_slot)
42 return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
46 * The UEFI memory descriptors have a virtual address field that is only used
47 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
48 * is unused here, we can reuse it to keep track of each descriptor's slot
51 #define MD_NUM_SLOTS(md) ((md)->virt_addr)
53 efi_status_t efi_random_alloc(unsigned long size,
56 unsigned long random_seed)
58 unsigned long map_size, desc_size, total_slots = 0, target_slot;
59 unsigned long buff_size;
61 efi_memory_desc_t *memory_map;
63 struct efi_boot_memmap map;
65 map.map = &memory_map;
66 map.map_size = &map_size;
67 map.desc_size = &desc_size;
70 map.buff_size = &buff_size;
72 status = efi_get_memory_map(&map);
73 if (status != EFI_SUCCESS)
76 if (align < EFI_ALLOC_ALIGN)
77 align = EFI_ALLOC_ALIGN;
79 size = round_up(size, EFI_ALLOC_ALIGN);
81 /* count the suitable slots in each memory map entry */
82 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
83 efi_memory_desc_t *md = (void *)memory_map + map_offset;
86 slots = get_entry_num_slots(md, size, ilog2(align));
87 MD_NUM_SLOTS(md) = slots;
91 /* find a random number between 0 and total_slots */
92 target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
95 * target_slot is now a value in the range [0, total_slots), and so
96 * it corresponds with exactly one of the suitable slots we recorded
97 * when iterating over the memory map the first time around.
99 * So iterate over the memory map again, subtracting the number of
100 * slots of each entry at each iteration, until we have found the entry
101 * that covers our chosen slot. Use the residual value of target_slot
102 * to calculate the randomly chosen address, and allocate it directly
103 * using EFI_ALLOCATE_ADDRESS.
105 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
106 efi_memory_desc_t *md = (void *)memory_map + map_offset;
107 efi_physical_addr_t target;
110 if (target_slot >= MD_NUM_SLOTS(md)) {
111 target_slot -= MD_NUM_SLOTS(md);
115 target = round_up(md->phys_addr, align) + target_slot * align;
116 pages = size / EFI_PAGE_SIZE;
118 status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
119 EFI_LOADER_DATA, pages, &target);
120 if (status == EFI_SUCCESS)
125 efi_bs_call(free_pool, memory_map);