summaryrefslogtreecommitdiff
path: root/drivers/firmware/efi/libstub/randomalloc.c
blob: 7e185285955021cb66a1a3a5fb4d6c24fc651b33 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
 */

#include <linux/efi.h>
#include <linux/log2.h>
#include <asm/efi.h>

#include "efistub.h"

/*
 * Return the number of slots covered by this entry, i.e., the number of
 * addresses it covers that are suitably aligned and supply enough room
 * for the allocation.
 */
static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
					 unsigned long size,
					 unsigned long align_shift,
					 u64 alloc_min, u64 alloc_max)
{
	unsigned long align = 1UL << align_shift;
	u64 first_slot, last_slot, region_end;

	if (md->type != EFI_CONVENTIONAL_MEMORY)
		return 0;

	if (efi_soft_reserve_enabled() &&
	    (md->attribute & EFI_MEMORY_SP))
		return 0;

	region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
			 alloc_max);
	if (region_end < size)
		return 0;

	first_slot = round_up(max(md->phys_addr, alloc_min), align);
	last_slot = round_down(region_end - size + 1, align);

	if (first_slot > last_slot)
		return 0;

	return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
}

/*
 * The UEFI memory descriptors have a virtual address field that is only used
 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
 * is unused here, we can reuse it to keep track of each descriptor's slot
 * count.
 */
#define MD_NUM_SLOTS(md)	((md)->virt_addr)

efi_status_t efi_random_alloc(unsigned long size,
			      unsigned long align,
			      unsigned long *addr,
			      unsigned long random_seed,
			      int memory_type,
			      unsigned long alloc_min,
			      unsigned long alloc_max)
{
	unsigned long total_slots = 0, target_slot;
	unsigned long total_mirrored_slots = 0;
	struct efi_boot_memmap *map;
	efi_status_t status;
	int map_offset;

	status = efi_get_memory_map(&map, false);
	if (status != EFI_SUCCESS)
		return status;

	if (align < EFI_ALLOC_ALIGN)
		align = EFI_ALLOC_ALIGN;

	size = round_up(size, EFI_ALLOC_ALIGN);

	/* count the suitable slots in each memory map entry */
	for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
		efi_memory_desc_t *md = (void *)map->map + map_offset;
		unsigned long slots;

		slots = get_entry_num_slots(md, size, ilog2(align), alloc_min,
					    alloc_max);
		MD_NUM_SLOTS(md) = slots;
		total_slots += slots;
		if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
			total_mirrored_slots += slots;
	}

	/* consider only mirrored slots for randomization if any exist */
	if (total_mirrored_slots > 0)
		total_slots = total_mirrored_slots;

	/* find a random number between 0 and total_slots */
	target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;

	/*
	 * target_slot is now a value in the range [0, total_slots), and so
	 * it corresponds with exactly one of the suitable slots we recorded
	 * when iterating over the memory map the first time around.
	 *
	 * So iterate over the memory map again, subtracting the number of
	 * slots of each entry at each iteration, until we have found the entry
	 * that covers our chosen slot. Use the residual value of target_slot
	 * to calculate the randomly chosen address, and allocate it directly
	 * using EFI_ALLOCATE_ADDRESS.
	 */
	status = EFI_OUT_OF_RESOURCES;
	for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
		efi_memory_desc_t *md = (void *)map->map + map_offset;
		efi_physical_addr_t target;
		unsigned long pages;

		if (total_mirrored_slots > 0 &&
		    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
			continue;

		if (target_slot >= MD_NUM_SLOTS(md)) {
			target_slot -= MD_NUM_SLOTS(md);
			continue;
		}

		target = round_up(max(md->phys_addr, alloc_min), align) + target_slot * align;
		pages = size / EFI_PAGE_SIZE;

		status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
				     memory_type, pages, &target);
		if (status == EFI_SUCCESS)
			*addr = target;
		break;
	}

	efi_bs_call(free_pool, map);

	return status;
}