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 unsigned long total_mirrored_slots = 0;
60 struct efi_boot_memmap *map;
61 efi_status_t status;
62 int map_offset;
63
64 status = efi_get_memory_map(&map, false);
65 if (status != EFI_SUCCESS)
66 return status;
67
68 if (align < EFI_ALLOC_ALIGN)
69 align = EFI_ALLOC_ALIGN;
70
71 size = round_up(size, EFI_ALLOC_ALIGN);
72
73 /* count the suitable slots in each memory map entry */
74 for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
75 efi_memory_desc_t *md = (void *)map->map + map_offset;
76 unsigned long slots;
77
78 slots = get_entry_num_slots(md, size, ilog2(align));
79 MD_NUM_SLOTS(md) = slots;
80 total_slots += slots;
81 if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
82 total_mirrored_slots += slots;
83 }
84
85 /* consider only mirrored slots for randomization if any exist */
86 if (total_mirrored_slots > 0)
87 total_slots = total_mirrored_slots;
88
89 /* find a random number between 0 and total_slots */
90 target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
91
92 /*
93 * target_slot is now a value in the range [0, total_slots), and so
94 * it corresponds with exactly one of the suitable slots we recorded
95 * when iterating over the memory map the first time around.
96 *
97 * So iterate over the memory map again, subtracting the number of
98 * slots of each entry at each iteration, until we have found the entry
99 * that covers our chosen slot. Use the residual value of target_slot
100 * to calculate the randomly chosen address, and allocate it directly
101 * using EFI_ALLOCATE_ADDRESS.
102 */
103 for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
104 efi_memory_desc_t *md = (void *)map->map + map_offset;
105 efi_physical_addr_t target;
106 unsigned long pages;
107
108 if (total_mirrored_slots > 0 &&
109 !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
110 continue;
111
112 if (target_slot >= MD_NUM_SLOTS(md)) {
113 target_slot -= MD_NUM_SLOTS(md);
114 continue;
115 }
116
117 target = round_up(md->phys_addr, align) + target_slot * align;
118 pages = size / EFI_PAGE_SIZE;
119
120 status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
121 EFI_LOADER_DATA, pages, &target);
122 if (status == EFI_SUCCESS)
123 *addr = target;
124 break;
125 }
126
127 efi_bs_call(free_pool, map);
128
129 return status;
130 }
131
