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df4e817b PT |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | /* | |
4 | * Copyright (c) 2021, Google LLC. | |
5 | * Pasha Tatashin <pasha.tatashin@soleen.com> | |
6 | */ | |
f15be1b8 | 7 | #include <linux/kstrtox.h> |
df4e817b PT |
8 | #include <linux/mm.h> |
9 | #include <linux/page_table_check.h> | |
10 | ||
11 | #undef pr_fmt | |
12 | #define pr_fmt(fmt) "page_table_check: " fmt | |
13 | ||
14 | struct page_table_check { | |
15 | atomic_t anon_map_count; | |
16 | atomic_t file_map_count; | |
17 | }; | |
18 | ||
19 | static bool __page_table_check_enabled __initdata = | |
20 | IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED); | |
21 | ||
22 | DEFINE_STATIC_KEY_TRUE(page_table_check_disabled); | |
23 | EXPORT_SYMBOL(page_table_check_disabled); | |
24 | ||
25 | static int __init early_page_table_check_param(char *buf) | |
26 | { | |
f15be1b8 | 27 | return kstrtobool(buf, &__page_table_check_enabled); |
df4e817b PT |
28 | } |
29 | ||
30 | early_param("page_table_check", early_page_table_check_param); | |
31 | ||
32 | static bool __init need_page_table_check(void) | |
33 | { | |
34 | return __page_table_check_enabled; | |
35 | } | |
36 | ||
37 | static void __init init_page_table_check(void) | |
38 | { | |
39 | if (!__page_table_check_enabled) | |
40 | return; | |
41 | static_branch_disable(&page_table_check_disabled); | |
42 | } | |
43 | ||
44 | struct page_ext_operations page_table_check_ops = { | |
45 | .size = sizeof(struct page_table_check), | |
46 | .need = need_page_table_check, | |
47 | .init = init_page_table_check, | |
48 | }; | |
49 | ||
50 | static struct page_table_check *get_page_table_check(struct page_ext *page_ext) | |
51 | { | |
52 | BUG_ON(!page_ext); | |
53 | return (void *)(page_ext) + page_table_check_ops.offset; | |
54 | } | |
55 | ||
df4e817b | 56 | /* |
3ae6d3e3 | 57 | * An entry is removed from the page table, decrement the counters for that page |
df4e817b PT |
58 | * verify that it is of correct type and counters do not become negative. |
59 | */ | |
60 | static void page_table_check_clear(struct mm_struct *mm, unsigned long addr, | |
61 | unsigned long pfn, unsigned long pgcnt) | |
62 | { | |
63 | struct page_ext *page_ext; | |
64 | struct page *page; | |
64d8b9e1 | 65 | unsigned long i; |
df4e817b | 66 | bool anon; |
df4e817b PT |
67 | |
68 | if (!pfn_valid(pfn)) | |
69 | return; | |
70 | ||
71 | page = pfn_to_page(pfn); | |
b1d5488a | 72 | page_ext = page_ext_get(page); |
df4e817b PT |
73 | anon = PageAnon(page); |
74 | ||
75 | for (i = 0; i < pgcnt; i++) { | |
76 | struct page_table_check *ptc = get_page_table_check(page_ext); | |
77 | ||
78 | if (anon) { | |
79 | BUG_ON(atomic_read(&ptc->file_map_count)); | |
80 | BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0); | |
81 | } else { | |
82 | BUG_ON(atomic_read(&ptc->anon_map_count)); | |
83 | BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0); | |
84 | } | |
85 | page_ext = page_ext_next(page_ext); | |
86 | } | |
b1d5488a | 87 | page_ext_put(page_ext); |
df4e817b PT |
88 | } |
89 | ||
90 | /* | |
3ae6d3e3 | 91 | * A new entry is added to the page table, increment the counters for that page |
df4e817b PT |
92 | * verify that it is of correct type and is not being mapped with a different |
93 | * type to a different process. | |
94 | */ | |
95 | static void page_table_check_set(struct mm_struct *mm, unsigned long addr, | |
96 | unsigned long pfn, unsigned long pgcnt, | |
97 | bool rw) | |
98 | { | |
99 | struct page_ext *page_ext; | |
100 | struct page *page; | |
64d8b9e1 | 101 | unsigned long i; |
df4e817b | 102 | bool anon; |
df4e817b PT |
103 | |
104 | if (!pfn_valid(pfn)) | |
105 | return; | |
106 | ||
107 | page = pfn_to_page(pfn); | |
b1d5488a | 108 | page_ext = page_ext_get(page); |
df4e817b PT |
109 | anon = PageAnon(page); |
110 | ||
111 | for (i = 0; i < pgcnt; i++) { | |
112 | struct page_table_check *ptc = get_page_table_check(page_ext); | |
113 | ||
114 | if (anon) { | |
115 | BUG_ON(atomic_read(&ptc->file_map_count)); | |
116 | BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw); | |
117 | } else { | |
118 | BUG_ON(atomic_read(&ptc->anon_map_count)); | |
119 | BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0); | |
120 | } | |
121 | page_ext = page_ext_next(page_ext); | |
122 | } | |
b1d5488a | 123 | page_ext_put(page_ext); |
df4e817b PT |
124 | } |
125 | ||
126 | /* | |
127 | * page is on free list, or is being allocated, verify that counters are zeroes | |
128 | * crash if they are not. | |
129 | */ | |
130 | void __page_table_check_zero(struct page *page, unsigned int order) | |
131 | { | |
b1d5488a | 132 | struct page_ext *page_ext; |
64d8b9e1 | 133 | unsigned long i; |
df4e817b | 134 | |
b1d5488a | 135 | page_ext = page_ext_get(page); |
df4e817b | 136 | BUG_ON(!page_ext); |
64d8b9e1 | 137 | for (i = 0; i < (1ul << order); i++) { |
df4e817b PT |
138 | struct page_table_check *ptc = get_page_table_check(page_ext); |
139 | ||
140 | BUG_ON(atomic_read(&ptc->anon_map_count)); | |
141 | BUG_ON(atomic_read(&ptc->file_map_count)); | |
142 | page_ext = page_ext_next(page_ext); | |
143 | } | |
b1d5488a | 144 | page_ext_put(page_ext); |
df4e817b PT |
145 | } |
146 | ||
147 | void __page_table_check_pte_clear(struct mm_struct *mm, unsigned long addr, | |
148 | pte_t pte) | |
149 | { | |
150 | if (&init_mm == mm) | |
151 | return; | |
152 | ||
153 | if (pte_user_accessible_page(pte)) { | |
154 | page_table_check_clear(mm, addr, pte_pfn(pte), | |
155 | PAGE_SIZE >> PAGE_SHIFT); | |
156 | } | |
157 | } | |
158 | EXPORT_SYMBOL(__page_table_check_pte_clear); | |
159 | ||
160 | void __page_table_check_pmd_clear(struct mm_struct *mm, unsigned long addr, | |
161 | pmd_t pmd) | |
162 | { | |
163 | if (&init_mm == mm) | |
164 | return; | |
165 | ||
166 | if (pmd_user_accessible_page(pmd)) { | |
167 | page_table_check_clear(mm, addr, pmd_pfn(pmd), | |
92fb0524 | 168 | PMD_SIZE >> PAGE_SHIFT); |
df4e817b PT |
169 | } |
170 | } | |
171 | EXPORT_SYMBOL(__page_table_check_pmd_clear); | |
172 | ||
173 | void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr, | |
174 | pud_t pud) | |
175 | { | |
176 | if (&init_mm == mm) | |
177 | return; | |
178 | ||
179 | if (pud_user_accessible_page(pud)) { | |
180 | page_table_check_clear(mm, addr, pud_pfn(pud), | |
92fb0524 | 181 | PUD_SIZE >> PAGE_SHIFT); |
df4e817b PT |
182 | } |
183 | } | |
184 | EXPORT_SYMBOL(__page_table_check_pud_clear); | |
185 | ||
186 | void __page_table_check_pte_set(struct mm_struct *mm, unsigned long addr, | |
187 | pte_t *ptep, pte_t pte) | |
188 | { | |
df4e817b PT |
189 | if (&init_mm == mm) |
190 | return; | |
191 | ||
64d8b9e1 | 192 | __page_table_check_pte_clear(mm, addr, *ptep); |
df4e817b PT |
193 | if (pte_user_accessible_page(pte)) { |
194 | page_table_check_set(mm, addr, pte_pfn(pte), | |
195 | PAGE_SIZE >> PAGE_SHIFT, | |
196 | pte_write(pte)); | |
197 | } | |
198 | } | |
199 | EXPORT_SYMBOL(__page_table_check_pte_set); | |
200 | ||
201 | void __page_table_check_pmd_set(struct mm_struct *mm, unsigned long addr, | |
202 | pmd_t *pmdp, pmd_t pmd) | |
203 | { | |
df4e817b PT |
204 | if (&init_mm == mm) |
205 | return; | |
206 | ||
64d8b9e1 | 207 | __page_table_check_pmd_clear(mm, addr, *pmdp); |
df4e817b PT |
208 | if (pmd_user_accessible_page(pmd)) { |
209 | page_table_check_set(mm, addr, pmd_pfn(pmd), | |
92fb0524 | 210 | PMD_SIZE >> PAGE_SHIFT, |
df4e817b PT |
211 | pmd_write(pmd)); |
212 | } | |
213 | } | |
214 | EXPORT_SYMBOL(__page_table_check_pmd_set); | |
215 | ||
216 | void __page_table_check_pud_set(struct mm_struct *mm, unsigned long addr, | |
217 | pud_t *pudp, pud_t pud) | |
218 | { | |
df4e817b PT |
219 | if (&init_mm == mm) |
220 | return; | |
221 | ||
64d8b9e1 | 222 | __page_table_check_pud_clear(mm, addr, *pudp); |
df4e817b PT |
223 | if (pud_user_accessible_page(pud)) { |
224 | page_table_check_set(mm, addr, pud_pfn(pud), | |
92fb0524 | 225 | PUD_SIZE >> PAGE_SHIFT, |
df4e817b PT |
226 | pud_write(pud)); |
227 | } | |
228 | } | |
229 | EXPORT_SYMBOL(__page_table_check_pud_set); | |
80110bbf PT |
230 | |
231 | void __page_table_check_pte_clear_range(struct mm_struct *mm, | |
232 | unsigned long addr, | |
233 | pmd_t pmd) | |
234 | { | |
235 | if (&init_mm == mm) | |
236 | return; | |
237 | ||
238 | if (!pmd_bad(pmd) && !pmd_leaf(pmd)) { | |
239 | pte_t *ptep = pte_offset_map(&pmd, addr); | |
240 | unsigned long i; | |
241 | ||
80110bbf PT |
242 | for (i = 0; i < PTRS_PER_PTE; i++) { |
243 | __page_table_check_pte_clear(mm, addr, *ptep); | |
244 | addr += PAGE_SIZE; | |
245 | ptep++; | |
246 | } | |
24c8e27e | 247 | pte_unmap(ptep - PTRS_PER_PTE); |
80110bbf PT |
248 | } |
249 | } |