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	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
53efi_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