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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 | */ | |
7 | #include <linux/mm.h> | |
8 | #include <linux/page_table_check.h> | |
9 | ||
10 | #undef pr_fmt | |
11 | #define pr_fmt(fmt) "page_table_check: " fmt | |
12 | ||
13 | struct page_table_check { | |
14 | atomic_t anon_map_count; | |
15 | atomic_t file_map_count; | |
16 | }; | |
17 | ||
18 | static bool __page_table_check_enabled __initdata = | |
19 | IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED); | |
20 | ||
21 | DEFINE_STATIC_KEY_TRUE(page_table_check_disabled); | |
22 | EXPORT_SYMBOL(page_table_check_disabled); | |
23 | ||
24 | static int __init early_page_table_check_param(char *buf) | |
25 | { | |
597da28e | 26 | return strtobool(buf, &__page_table_check_enabled); |
df4e817b PT |
27 | } |
28 | ||
29 | early_param("page_table_check", early_page_table_check_param); | |
30 | ||
31 | static bool __init need_page_table_check(void) | |
32 | { | |
33 | return __page_table_check_enabled; | |
34 | } | |
35 | ||
36 | static void __init init_page_table_check(void) | |
37 | { | |
38 | if (!__page_table_check_enabled) | |
39 | return; | |
40 | static_branch_disable(&page_table_check_disabled); | |
41 | } | |
42 | ||
43 | struct page_ext_operations page_table_check_ops = { | |
44 | .size = sizeof(struct page_table_check), | |
45 | .need = need_page_table_check, | |
46 | .init = init_page_table_check, | |
47 | }; | |
48 | ||
49 | static struct page_table_check *get_page_table_check(struct page_ext *page_ext) | |
50 | { | |
51 | BUG_ON(!page_ext); | |
52 | return (void *)(page_ext) + page_table_check_ops.offset; | |
53 | } | |
54 | ||
55 | static inline bool pte_user_accessible_page(pte_t pte) | |
56 | { | |
57 | return (pte_val(pte) & _PAGE_PRESENT) && (pte_val(pte) & _PAGE_USER); | |
58 | } | |
59 | ||
60 | static inline bool pmd_user_accessible_page(pmd_t pmd) | |
61 | { | |
62 | return pmd_leaf(pmd) && (pmd_val(pmd) & _PAGE_PRESENT) && | |
63 | (pmd_val(pmd) & _PAGE_USER); | |
64 | } | |
65 | ||
66 | static inline bool pud_user_accessible_page(pud_t pud) | |
67 | { | |
68 | return pud_leaf(pud) && (pud_val(pud) & _PAGE_PRESENT) && | |
69 | (pud_val(pud) & _PAGE_USER); | |
70 | } | |
71 | ||
72 | /* | |
73 | * An enty is removed from the page table, decrement the counters for that page | |
74 | * verify that it is of correct type and counters do not become negative. | |
75 | */ | |
76 | static void page_table_check_clear(struct mm_struct *mm, unsigned long addr, | |
77 | unsigned long pfn, unsigned long pgcnt) | |
78 | { | |
79 | struct page_ext *page_ext; | |
80 | struct page *page; | |
64d8b9e1 | 81 | unsigned long i; |
df4e817b | 82 | bool anon; |
df4e817b PT |
83 | |
84 | if (!pfn_valid(pfn)) | |
85 | return; | |
86 | ||
87 | page = pfn_to_page(pfn); | |
88 | page_ext = lookup_page_ext(page); | |
89 | anon = PageAnon(page); | |
90 | ||
91 | for (i = 0; i < pgcnt; i++) { | |
92 | struct page_table_check *ptc = get_page_table_check(page_ext); | |
93 | ||
94 | if (anon) { | |
95 | BUG_ON(atomic_read(&ptc->file_map_count)); | |
96 | BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0); | |
97 | } else { | |
98 | BUG_ON(atomic_read(&ptc->anon_map_count)); | |
99 | BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0); | |
100 | } | |
101 | page_ext = page_ext_next(page_ext); | |
102 | } | |
103 | } | |
104 | ||
105 | /* | |
106 | * A new enty is added to the page table, increment the counters for that page | |
107 | * verify that it is of correct type and is not being mapped with a different | |
108 | * type to a different process. | |
109 | */ | |
110 | static void page_table_check_set(struct mm_struct *mm, unsigned long addr, | |
111 | unsigned long pfn, unsigned long pgcnt, | |
112 | bool rw) | |
113 | { | |
114 | struct page_ext *page_ext; | |
115 | struct page *page; | |
64d8b9e1 | 116 | unsigned long i; |
df4e817b | 117 | bool anon; |
df4e817b PT |
118 | |
119 | if (!pfn_valid(pfn)) | |
120 | return; | |
121 | ||
122 | page = pfn_to_page(pfn); | |
123 | page_ext = lookup_page_ext(page); | |
124 | anon = PageAnon(page); | |
125 | ||
126 | for (i = 0; i < pgcnt; i++) { | |
127 | struct page_table_check *ptc = get_page_table_check(page_ext); | |
128 | ||
129 | if (anon) { | |
130 | BUG_ON(atomic_read(&ptc->file_map_count)); | |
131 | BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw); | |
132 | } else { | |
133 | BUG_ON(atomic_read(&ptc->anon_map_count)); | |
134 | BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0); | |
135 | } | |
136 | page_ext = page_ext_next(page_ext); | |
137 | } | |
138 | } | |
139 | ||
140 | /* | |
141 | * page is on free list, or is being allocated, verify that counters are zeroes | |
142 | * crash if they are not. | |
143 | */ | |
144 | void __page_table_check_zero(struct page *page, unsigned int order) | |
145 | { | |
146 | struct page_ext *page_ext = lookup_page_ext(page); | |
64d8b9e1 | 147 | unsigned long i; |
df4e817b PT |
148 | |
149 | BUG_ON(!page_ext); | |
64d8b9e1 | 150 | for (i = 0; i < (1ul << order); i++) { |
df4e817b PT |
151 | struct page_table_check *ptc = get_page_table_check(page_ext); |
152 | ||
153 | BUG_ON(atomic_read(&ptc->anon_map_count)); | |
154 | BUG_ON(atomic_read(&ptc->file_map_count)); | |
155 | page_ext = page_ext_next(page_ext); | |
156 | } | |
157 | } | |
158 | ||
159 | void __page_table_check_pte_clear(struct mm_struct *mm, unsigned long addr, | |
160 | pte_t pte) | |
161 | { | |
162 | if (&init_mm == mm) | |
163 | return; | |
164 | ||
165 | if (pte_user_accessible_page(pte)) { | |
166 | page_table_check_clear(mm, addr, pte_pfn(pte), | |
167 | PAGE_SIZE >> PAGE_SHIFT); | |
168 | } | |
169 | } | |
170 | EXPORT_SYMBOL(__page_table_check_pte_clear); | |
171 | ||
172 | void __page_table_check_pmd_clear(struct mm_struct *mm, unsigned long addr, | |
173 | pmd_t pmd) | |
174 | { | |
175 | if (&init_mm == mm) | |
176 | return; | |
177 | ||
178 | if (pmd_user_accessible_page(pmd)) { | |
179 | page_table_check_clear(mm, addr, pmd_pfn(pmd), | |
180 | PMD_PAGE_SIZE >> PAGE_SHIFT); | |
181 | } | |
182 | } | |
183 | EXPORT_SYMBOL(__page_table_check_pmd_clear); | |
184 | ||
185 | void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr, | |
186 | pud_t pud) | |
187 | { | |
188 | if (&init_mm == mm) | |
189 | return; | |
190 | ||
191 | if (pud_user_accessible_page(pud)) { | |
192 | page_table_check_clear(mm, addr, pud_pfn(pud), | |
193 | PUD_PAGE_SIZE >> PAGE_SHIFT); | |
194 | } | |
195 | } | |
196 | EXPORT_SYMBOL(__page_table_check_pud_clear); | |
197 | ||
198 | void __page_table_check_pte_set(struct mm_struct *mm, unsigned long addr, | |
199 | pte_t *ptep, pte_t pte) | |
200 | { | |
df4e817b PT |
201 | if (&init_mm == mm) |
202 | return; | |
203 | ||
64d8b9e1 | 204 | __page_table_check_pte_clear(mm, addr, *ptep); |
df4e817b PT |
205 | if (pte_user_accessible_page(pte)) { |
206 | page_table_check_set(mm, addr, pte_pfn(pte), | |
207 | PAGE_SIZE >> PAGE_SHIFT, | |
208 | pte_write(pte)); | |
209 | } | |
210 | } | |
211 | EXPORT_SYMBOL(__page_table_check_pte_set); | |
212 | ||
213 | void __page_table_check_pmd_set(struct mm_struct *mm, unsigned long addr, | |
214 | pmd_t *pmdp, pmd_t pmd) | |
215 | { | |
df4e817b PT |
216 | if (&init_mm == mm) |
217 | return; | |
218 | ||
64d8b9e1 | 219 | __page_table_check_pmd_clear(mm, addr, *pmdp); |
df4e817b PT |
220 | if (pmd_user_accessible_page(pmd)) { |
221 | page_table_check_set(mm, addr, pmd_pfn(pmd), | |
222 | PMD_PAGE_SIZE >> PAGE_SHIFT, | |
223 | pmd_write(pmd)); | |
224 | } | |
225 | } | |
226 | EXPORT_SYMBOL(__page_table_check_pmd_set); | |
227 | ||
228 | void __page_table_check_pud_set(struct mm_struct *mm, unsigned long addr, | |
229 | pud_t *pudp, pud_t pud) | |
230 | { | |
df4e817b PT |
231 | if (&init_mm == mm) |
232 | return; | |
233 | ||
64d8b9e1 | 234 | __page_table_check_pud_clear(mm, addr, *pudp); |
df4e817b PT |
235 | if (pud_user_accessible_page(pud)) { |
236 | page_table_check_set(mm, addr, pud_pfn(pud), | |
237 | PUD_PAGE_SIZE >> PAGE_SHIFT, | |
238 | pud_write(pud)); | |
239 | } | |
240 | } | |
241 | EXPORT_SYMBOL(__page_table_check_pud_set); | |
80110bbf PT |
242 | |
243 | void __page_table_check_pte_clear_range(struct mm_struct *mm, | |
244 | unsigned long addr, | |
245 | pmd_t pmd) | |
246 | { | |
247 | if (&init_mm == mm) | |
248 | return; | |
249 | ||
250 | if (!pmd_bad(pmd) && !pmd_leaf(pmd)) { | |
251 | pte_t *ptep = pte_offset_map(&pmd, addr); | |
252 | unsigned long i; | |
253 | ||
254 | pte_unmap(ptep); | |
255 | for (i = 0; i < PTRS_PER_PTE; i++) { | |
256 | __page_table_check_pte_clear(mm, addr, *ptep); | |
257 | addr += PAGE_SIZE; | |
258 | ptep++; | |
259 | } | |
260 | } | |
261 | } |