1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
|
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2021, Google LLC.
* Pasha Tatashin <pasha.tatashin@soleen.com>
*/
#include <linux/mm.h>
#include <linux/page_table_check.h>
#undef pr_fmt
#define pr_fmt(fmt) "page_table_check: " fmt
struct page_table_check {
atomic_t anon_map_count;
atomic_t file_map_count;
};
static bool __page_table_check_enabled __initdata =
IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED);
DEFINE_STATIC_KEY_TRUE(page_table_check_disabled);
EXPORT_SYMBOL(page_table_check_disabled);
static int __init early_page_table_check_param(char *buf)
{
if (!buf)
return -EINVAL;
if (strcmp(buf, "on") == 0)
__page_table_check_enabled = true;
else if (strcmp(buf, "off") == 0)
__page_table_check_enabled = false;
return 0;
}
early_param("page_table_check", early_page_table_check_param);
static bool __init need_page_table_check(void)
{
return __page_table_check_enabled;
}
static void __init init_page_table_check(void)
{
if (!__page_table_check_enabled)
return;
static_branch_disable(&page_table_check_disabled);
}
struct page_ext_operations page_table_check_ops = {
.size = sizeof(struct page_table_check),
.need = need_page_table_check,
.init = init_page_table_check,
};
static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
{
BUG_ON(!page_ext);
return (void *)(page_ext) + page_table_check_ops.offset;
}
static inline bool pte_user_accessible_page(pte_t pte)
{
return (pte_val(pte) & _PAGE_PRESENT) && (pte_val(pte) & _PAGE_USER);
}
static inline bool pmd_user_accessible_page(pmd_t pmd)
{
return pmd_leaf(pmd) && (pmd_val(pmd) & _PAGE_PRESENT) &&
(pmd_val(pmd) & _PAGE_USER);
}
static inline bool pud_user_accessible_page(pud_t pud)
{
return pud_leaf(pud) && (pud_val(pud) & _PAGE_PRESENT) &&
(pud_val(pud) & _PAGE_USER);
}
/*
* An enty is removed from the page table, decrement the counters for that page
* verify that it is of correct type and counters do not become negative.
*/
static void page_table_check_clear(struct mm_struct *mm, unsigned long addr,
unsigned long pfn, unsigned long pgcnt)
{
struct page_ext *page_ext;
struct page *page;
unsigned long i;
bool anon;
if (!pfn_valid(pfn))
return;
page = pfn_to_page(pfn);
page_ext = lookup_page_ext(page);
anon = PageAnon(page);
for (i = 0; i < pgcnt; i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
if (anon) {
BUG_ON(atomic_read(&ptc->file_map_count));
BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0);
} else {
BUG_ON(atomic_read(&ptc->anon_map_count));
BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
}
page_ext = page_ext_next(page_ext);
}
}
/*
* A new enty is added to the page table, increment the counters for that page
* verify that it is of correct type and is not being mapped with a different
* type to a different process.
*/
static void page_table_check_set(struct mm_struct *mm, unsigned long addr,
unsigned long pfn, unsigned long pgcnt,
bool rw)
{
struct page_ext *page_ext;
struct page *page;
unsigned long i;
bool anon;
if (!pfn_valid(pfn))
return;
page = pfn_to_page(pfn);
page_ext = lookup_page_ext(page);
anon = PageAnon(page);
for (i = 0; i < pgcnt; i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
if (anon) {
BUG_ON(atomic_read(&ptc->file_map_count));
BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);
} else {
BUG_ON(atomic_read(&ptc->anon_map_count));
BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0);
}
page_ext = page_ext_next(page_ext);
}
}
/*
* page is on free list, or is being allocated, verify that counters are zeroes
* crash if they are not.
*/
void __page_table_check_zero(struct page *page, unsigned int order)
{
struct page_ext *page_ext = lookup_page_ext(page);
unsigned long i;
BUG_ON(!page_ext);
for (i = 0; i < (1ul << order); i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
BUG_ON(atomic_read(&ptc->anon_map_count));
BUG_ON(atomic_read(&ptc->file_map_count));
page_ext = page_ext_next(page_ext);
}
}
void __page_table_check_pte_clear(struct mm_struct *mm, unsigned long addr,
pte_t pte)
{
if (&init_mm == mm)
return;
if (pte_user_accessible_page(pte)) {
page_table_check_clear(mm, addr, pte_pfn(pte),
PAGE_SIZE >> PAGE_SHIFT);
}
}
EXPORT_SYMBOL(__page_table_check_pte_clear);
void __page_table_check_pmd_clear(struct mm_struct *mm, unsigned long addr,
pmd_t pmd)
{
if (&init_mm == mm)
return;
if (pmd_user_accessible_page(pmd)) {
page_table_check_clear(mm, addr, pmd_pfn(pmd),
PMD_PAGE_SIZE >> PAGE_SHIFT);
}
}
EXPORT_SYMBOL(__page_table_check_pmd_clear);
void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr,
pud_t pud)
{
if (&init_mm == mm)
return;
if (pud_user_accessible_page(pud)) {
page_table_check_clear(mm, addr, pud_pfn(pud),
PUD_PAGE_SIZE >> PAGE_SHIFT);
}
}
EXPORT_SYMBOL(__page_table_check_pud_clear);
void __page_table_check_pte_set(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
if (&init_mm == mm)
return;
__page_table_check_pte_clear(mm, addr, *ptep);
if (pte_user_accessible_page(pte)) {
page_table_check_set(mm, addr, pte_pfn(pte),
PAGE_SIZE >> PAGE_SHIFT,
pte_write(pte));
}
}
EXPORT_SYMBOL(__page_table_check_pte_set);
void __page_table_check_pmd_set(struct mm_struct *mm, unsigned long addr,
pmd_t *pmdp, pmd_t pmd)
{
if (&init_mm == mm)
return;
__page_table_check_pmd_clear(mm, addr, *pmdp);
if (pmd_user_accessible_page(pmd)) {
page_table_check_set(mm, addr, pmd_pfn(pmd),
PMD_PAGE_SIZE >> PAGE_SHIFT,
pmd_write(pmd));
}
}
EXPORT_SYMBOL(__page_table_check_pmd_set);
void __page_table_check_pud_set(struct mm_struct *mm, unsigned long addr,
pud_t *pudp, pud_t pud)
{
if (&init_mm == mm)
return;
__page_table_check_pud_clear(mm, addr, *pudp);
if (pud_user_accessible_page(pud)) {
page_table_check_set(mm, addr, pud_pfn(pud),
PUD_PAGE_SIZE >> PAGE_SHIFT,
pud_write(pud));
}
}
EXPORT_SYMBOL(__page_table_check_pud_set);
void __page_table_check_pte_clear_range(struct mm_struct *mm,
unsigned long addr,
pmd_t pmd)
{
if (&init_mm == mm)
return;
if (!pmd_bad(pmd) && !pmd_leaf(pmd)) {
pte_t *ptep = pte_offset_map(&pmd, addr);
unsigned long i;
pte_unmap(ptep);
for (i = 0; i < PTRS_PER_PTE; i++) {
__page_table_check_pte_clear(mm, addr, *ptep);
addr += PAGE_SIZE;
ptep++;
}
}
}
|
