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