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  */
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 
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