Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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linux
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 */
17static 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
34 first_slot = round_up(md->phys_addr, align);
35 last_slot = round_down(region_end - size + 1, align);
36
37 if (first_slot > last_slot)
38 return 0;
39
40 return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
41}
42
43/*
44 * The UEFI memory descriptors have a virtual address field that is only used
45 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
46 * is unused here, we can reuse it to keep track of each descriptor's slot
47 * count.
48 */
49#define MD_NUM_SLOTS(md) ((md)->virt_addr)
50
51efi_status_t efi_random_alloc(unsigned long size,
52 unsigned long align,
53 unsigned long *addr,
54 unsigned long random_seed)
55{
56 unsigned long map_size, desc_size, total_slots = 0, target_slot;
57 unsigned long buff_size;
58 efi_status_t status;
59 efi_memory_desc_t *memory_map;
60 int map_offset;
61 struct efi_boot_memmap map;
62
63 map.map = &memory_map;
64 map.map_size = &map_size;
65 map.desc_size = &desc_size;
66 map.desc_ver = NULL;
67 map.key_ptr = NULL;
68 map.buff_size = &buff_size;
69
70 status = efi_get_memory_map(&map);
71 if (status != EFI_SUCCESS)
72 return status;
73
74 if (align < EFI_ALLOC_ALIGN)
75 align = EFI_ALLOC_ALIGN;
76
77 /* count the suitable slots in each memory map entry */
78 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
79 efi_memory_desc_t *md = (void *)memory_map + map_offset;
80 unsigned long slots;
81
82 slots = get_entry_num_slots(md, size, ilog2(align));
83 MD_NUM_SLOTS(md) = slots;
84 total_slots += slots;
85 }
86
87 /* find a random number between 0 and total_slots */
88 target_slot = (total_slots * (u16)random_seed) >> 16;
89
90 /*
91 * target_slot is now a value in the range [0, total_slots), and so
92 * it corresponds with exactly one of the suitable slots we recorded
93 * when iterating over the memory map the first time around.
94 *
95 * So iterate over the memory map again, subtracting the number of
96 * slots of each entry at each iteration, until we have found the entry
97 * that covers our chosen slot. Use the residual value of target_slot
98 * to calculate the randomly chosen address, and allocate it directly
99 * using EFI_ALLOCATE_ADDRESS.
100 */
101 for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
102 efi_memory_desc_t *md = (void *)memory_map + map_offset;
103 efi_physical_addr_t target;
104 unsigned long pages;
105
106 if (target_slot >= MD_NUM_SLOTS(md)) {
107 target_slot -= MD_NUM_SLOTS(md);
108 continue;
109 }
110
111 target = round_up(md->phys_addr, align) + target_slot * align;
112 pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
113
114 status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
115 EFI_LOADER_DATA, pages, &target);
116 if (status == EFI_SUCCESS)
117 *addr = target;
118 break;
119 }
120
121 efi_bs_call(free_pool, memory_map);
122
123 return status;
124}