1 /*
2 * This code is used on x86_64 to create page table identity mappings on
3 * demand by building up a new set of page tables (or appending to the
4 * existing ones), and then switching over to them when ready.
5 *
6 * Copyright (C) 2015-2016 Yinghai Lu
7 * Copyright (C) 2016 Kees Cook
8 */
9
10 /*
11 * Since we're dealing with identity mappings, physical and virtual
12 * addresses are the same, so override these defines which are ultimately
13 * used by the headers in misc.h.
14 */
15 #define __pa(x) ((unsigned long)(x))
16 #define __va(x) ((void *)((unsigned long)(x)))
17
18 #include "misc.h"
19
20 /* These actually do the work of building the kernel identity maps. */
21 #include <asm/init.h>
22 #include <asm/pgtable.h>
23 /* Use the static base for this part of the boot process */
24 #undef __PAGE_OFFSET
25 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
26 #include "../../mm/ident_map.c"
27
28 /* Used by pgtable.h asm code to force instruction serialization. */
29 unsigned long __force_order;
30
31 /* Used to track our page table allocation area. */
32 struct alloc_pgt_data {
33 unsigned char *pgt_buf;
34 unsigned long pgt_buf_size;
35 unsigned long pgt_buf_offset;
36 };
37
38 /*
39 * Allocates space for a page table entry, using struct alloc_pgt_data
40 * above. Besides the local callers, this is used as the allocation
41 * callback in mapping_info below.
42 */
alloc_pgt_page(void * context)43 static void *alloc_pgt_page(void *context)
44 {
45 struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
46 unsigned char *entry;
47
48 /* Validate there is space available for a new page. */
49 if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
50 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
51 debug_putaddr(pages->pgt_buf_offset);
52 debug_putaddr(pages->pgt_buf_size);
53 return NULL;
54 }
55
56 entry = pages->pgt_buf + pages->pgt_buf_offset;
57 pages->pgt_buf_offset += PAGE_SIZE;
58
59 return entry;
60 }
61
62 /* Used to track our allocated page tables. */
63 static struct alloc_pgt_data pgt_data;
64
65 /* The top level page table entry pointer. */
66 static unsigned long level4p;
67
68 /*
69 * Mapping information structure passed to kernel_ident_mapping_init().
70 * Due to relocation, pointers must be assigned at run time not build time.
71 */
72 static struct x86_mapping_info mapping_info = {
73 .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
74 };
75
76 /* Locates and clears a region for a new top level page table. */
initialize_identity_maps(void)77 void initialize_identity_maps(void)
78 {
79 /* Init mapping_info with run-time function/buffer pointers. */
80 mapping_info.alloc_pgt_page = alloc_pgt_page;
81 mapping_info.context = &pgt_data;
82
83 /*
84 * It should be impossible for this not to already be true,
85 * but since calling this a second time would rewind the other
86 * counters, let's just make sure this is reset too.
87 */
88 pgt_data.pgt_buf_offset = 0;
89
90 /*
91 * If we came here via startup_32(), cr3 will be _pgtable already
92 * and we must append to the existing area instead of entirely
93 * overwriting it.
94 */
95 level4p = read_cr3();
96 if (level4p == (unsigned long)_pgtable) {
97 debug_putstr("booted via startup_32()\n");
98 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
99 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
100 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
101 } else {
102 debug_putstr("booted via startup_64()\n");
103 pgt_data.pgt_buf = _pgtable;
104 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
105 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
106 level4p = (unsigned long)alloc_pgt_page(&pgt_data);
107 }
108 }
109
110 /*
111 * Adds the specified range to what will become the new identity mappings.
112 * Once all ranges have been added, the new mapping is activated by calling
113 * finalize_identity_maps() below.
114 */
add_identity_map(unsigned long start,unsigned long size)115 void add_identity_map(unsigned long start, unsigned long size)
116 {
117 unsigned long end = start + size;
118
119 /* Align boundary to 2M. */
120 start = round_down(start, PMD_SIZE);
121 end = round_up(end, PMD_SIZE);
122 if (start >= end)
123 return;
124
125 /* Build the mapping. */
126 kernel_ident_mapping_init(&mapping_info, (pgd_t *)level4p,
127 start, end);
128 }
129
130 /*
131 * This switches the page tables to the new level4 that has been built
132 * via calls to add_identity_map() above. If booted via startup_32(),
133 * this is effectively a no-op.
134 */
finalize_identity_maps(void)135 void finalize_identity_maps(void)
136 {
137 write_cr3(level4p);
138 }
139