1 /*
2  * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License version 2 as
6  * published by the Free Software Foundation.
7  *
8  */
9 
10 #include <linux/efi.h>
11 #include <asm/efi.h>
12 
13 #include "efistub.h"
14 
15 struct efi_rng_protocol {
16 	efi_status_t (*get_info)(struct efi_rng_protocol *,
17 				 unsigned long *, efi_guid_t *);
18 	efi_status_t (*get_rng)(struct efi_rng_protocol *,
19 				efi_guid_t *, unsigned long, u8 *out);
20 };
21 
22 efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
23 				  unsigned long size, u8 *out)
24 {
25 	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
26 	efi_status_t status;
27 	struct efi_rng_protocol *rng;
28 
29 	status = efi_call_early(locate_protocol, &rng_proto, NULL,
30 				(void **)&rng);
31 	if (status != EFI_SUCCESS)
32 		return status;
33 
34 	return rng->get_rng(rng, NULL, size, out);
35 }
36 
37 /*
38  * Return the number of slots covered by this entry, i.e., the number of
39  * addresses it covers that are suitably aligned and supply enough room
40  * for the allocation.
41  */
42 static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
43 					 unsigned long size,
44 					 unsigned long align)
45 {
46 	u64 start, end;
47 
48 	if (md->type != EFI_CONVENTIONAL_MEMORY)
49 		return 0;
50 
51 	start = round_up(md->phys_addr, align);
52 	end = round_down(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - size,
53 			 align);
54 
55 	if (start > end)
56 		return 0;
57 
58 	return (end - start + 1) / align;
59 }
60 
61 /*
62  * The UEFI memory descriptors have a virtual address field that is only used
63  * when installing the virtual mapping using SetVirtualAddressMap(). Since it
64  * is unused here, we can reuse it to keep track of each descriptor's slot
65  * count.
66  */
67 #define MD_NUM_SLOTS(md)	((md)->virt_addr)
68 
69 efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
70 			      unsigned long size,
71 			      unsigned long align,
72 			      unsigned long *addr,
73 			      unsigned long random_seed)
74 {
75 	unsigned long map_size, desc_size, total_slots = 0, target_slot;
76 	efi_status_t status;
77 	efi_memory_desc_t *memory_map;
78 	int map_offset;
79 
80 	status = efi_get_memory_map(sys_table_arg, &memory_map, &map_size,
81 				    &desc_size, NULL, NULL);
82 	if (status != EFI_SUCCESS)
83 		return status;
84 
85 	if (align < EFI_ALLOC_ALIGN)
86 		align = EFI_ALLOC_ALIGN;
87 
88 	/* count the suitable slots in each memory map entry */
89 	for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
90 		efi_memory_desc_t *md = (void *)memory_map + map_offset;
91 		unsigned long slots;
92 
93 		slots = get_entry_num_slots(md, size, align);
94 		MD_NUM_SLOTS(md) = slots;
95 		total_slots += slots;
96 	}
97 
98 	/* find a random number between 0 and total_slots */
99 	target_slot = (total_slots * (u16)random_seed) >> 16;
100 
101 	/*
102 	 * target_slot is now a value in the range [0, total_slots), and so
103 	 * it corresponds with exactly one of the suitable slots we recorded
104 	 * when iterating over the memory map the first time around.
105 	 *
106 	 * So iterate over the memory map again, subtracting the number of
107 	 * slots of each entry at each iteration, until we have found the entry
108 	 * that covers our chosen slot. Use the residual value of target_slot
109 	 * to calculate the randomly chosen address, and allocate it directly
110 	 * using EFI_ALLOCATE_ADDRESS.
111 	 */
112 	for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
113 		efi_memory_desc_t *md = (void *)memory_map + map_offset;
114 		efi_physical_addr_t target;
115 		unsigned long pages;
116 
117 		if (target_slot >= MD_NUM_SLOTS(md)) {
118 			target_slot -= MD_NUM_SLOTS(md);
119 			continue;
120 		}
121 
122 		target = round_up(md->phys_addr, align) + target_slot * align;
123 		pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
124 
125 		status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
126 					EFI_LOADER_DATA, pages, &target);
127 		if (status == EFI_SUCCESS)
128 			*addr = target;
129 		break;
130 	}
131 
132 	efi_call_early(free_pool, memory_map);
133 
134 	return status;
135 }
136