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 <linux/log2.h>
8 #include <asm/efi.h>
9
10 #include "efistub.h"
11
12 /*
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
15 * for the allocation.
16 */
get_entry_num_slots(efi_memory_desc_t *md, unsigned long size, unsigned long align_shift)17 static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
18 unsigned long size,
19 unsigned long align_shift)
20 {
21 unsigned long align = 1UL << align_shift;
22 u64 first_slot, last_slot, region_end;
23
24 if (md->type != EFI_CONVENTIONAL_MEMORY)
25 return 0;
26
27 if (efi_soft_reserve_enabled() &&
28 (md->attribute & EFI_MEMORY_SP))
29 return 0;
30
31 region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
32 (u64)ULONG_MAX);
33 if (region_end < size)
34 return 0;
35
36 first_slot = round_up(md->phys_addr, align);
37 last_slot = round_down(region_end - size + 1, align);
38
39 if (first_slot > last_slot)
40 return 0;
41
42 return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
43 }
44
45 /*
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
49 * count.
50 */
51 #define MD_NUM_SLOTS(md) ((md)->virt_addr)
52
efi_random_alloc(unsigned long size, unsigned long align, unsigned long *addr, unsigned long random_seed)53 efi_status_t efi_random_alloc(unsigned long size,
54 unsigned long align,
55 unsigned long *addr,
56 unsigned long random_seed)
57 {
58 unsigned long total_slots = 0, target_slot;
59 struct efi_boot_memmap *map;
60 efi_status_t status;
61 int map_offset;
62
63 status = efi_get_memory_map(&map, false);
64 if (status != EFI_SUCCESS)
65 return status;
66
67 if (align < EFI_ALLOC_ALIGN)
68 align = EFI_ALLOC_ALIGN;
69
70 size = round_up(size, EFI_ALLOC_ALIGN);
71
72 /* count the suitable slots in each memory map entry */
73 for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
74 efi_memory_desc_t *md = (void *)map->map + map_offset;
75 unsigned long slots;
76
77 slots = get_entry_num_slots(md, size, ilog2(align));
78 MD_NUM_SLOTS(md) = slots;
79 total_slots += slots;
80 }
81
82 /* find a random number between 0 and total_slots */
83 target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
84
85 /*
86 * target_slot is now a value in the range [0, total_slots), and so
87 * it corresponds with exactly one of the suitable slots we recorded
88 * when iterating over the memory map the first time around.
89 *
90 * So iterate over the memory map again, subtracting the number of
91 * slots of each entry at each iteration, until we have found the entry
92 * that covers our chosen slot. Use the residual value of target_slot
93 * to calculate the randomly chosen address, and allocate it directly
94 * using EFI_ALLOCATE_ADDRESS.
95 */
96 for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
97 efi_memory_desc_t *md = (void *)map->map + map_offset;
98 efi_physical_addr_t target;
99 unsigned long pages;
100
101 if (target_slot >= MD_NUM_SLOTS(md)) {
102 target_slot -= MD_NUM_SLOTS(md);
103 continue;
104 }
105
106 target = round_up(md->phys_addr, align) + target_slot * align;
107 pages = size / EFI_PAGE_SIZE;
108
109 status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
110 EFI_LOADER_DATA, pages, &target);
111 if (status == EFI_SUCCESS)
112 *addr = target;
113 break;
114 }
115
116 efi_bs_call(free_pool, map);
117
118 return status;
119 }
120