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)EFI_ALLOC_LIMIT);
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 			      int memory_type)
58 {
59 	unsigned long total_slots = 0, target_slot;
60 	unsigned long total_mirrored_slots = 0;
61 	struct efi_boot_memmap *map;
62 	efi_status_t status;
63 	int map_offset;
64 
65 	status = efi_get_memory_map(&map, false);
66 	if (status != EFI_SUCCESS)
67 		return status;
68 
69 	if (align < EFI_ALLOC_ALIGN)
70 		align = EFI_ALLOC_ALIGN;
71 
72 	size = round_up(size, EFI_ALLOC_ALIGN);
73 
74 	/* count the suitable slots in each memory map entry */
75 	for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
76 		efi_memory_desc_t *md = (void *)map->map + map_offset;
77 		unsigned long slots;
78 
79 		slots = get_entry_num_slots(md, size, ilog2(align));
80 		MD_NUM_SLOTS(md) = slots;
81 		total_slots += slots;
82 		if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
83 			total_mirrored_slots += slots;
84 	}
85 
86 	/* consider only mirrored slots for randomization if any exist */
87 	if (total_mirrored_slots > 0)
88 		total_slots = total_mirrored_slots;
89 
90 	/* find a random number between 0 and total_slots */
91 	target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
92 
93 	/*
94 	 * target_slot is now a value in the range [0, total_slots), and so
95 	 * it corresponds with exactly one of the suitable slots we recorded
96 	 * when iterating over the memory map the first time around.
97 	 *
98 	 * So iterate over the memory map again, subtracting the number of
99 	 * slots of each entry at each iteration, until we have found the entry
100 	 * that covers our chosen slot. Use the residual value of target_slot
101 	 * to calculate the randomly chosen address, and allocate it directly
102 	 * using EFI_ALLOCATE_ADDRESS.
103 	 */
104 	for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
105 		efi_memory_desc_t *md = (void *)map->map + map_offset;
106 		efi_physical_addr_t target;
107 		unsigned long pages;
108 
109 		if (total_mirrored_slots > 0 &&
110 		    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
111 			continue;
112 
113 		if (target_slot >= MD_NUM_SLOTS(md)) {
114 			target_slot -= MD_NUM_SLOTS(md);
115 			continue;
116 		}
117 
118 		target = round_up(md->phys_addr, align) + target_slot * align;
119 		pages = size / EFI_PAGE_SIZE;
120 
121 		status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
122 				     memory_type, pages, &target);
123 		if (status == EFI_SUCCESS)
124 			*addr = target;
125 		break;
126 	}
127 
128 	efi_bs_call(free_pool, map);
129 
130 	return status;
131 }
132