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/kstrtox.h> 8 #include <linux/mm.h> 9 #include <linux/page_table_check.h> 10 #include <linux/swap.h> 11 #include <linux/swapops.h> 12 13 #undef pr_fmt 14 #define pr_fmt(fmt) "page_table_check: " fmt 15 16 struct page_table_check { 17 atomic_t anon_map_count; 18 atomic_t file_map_count; 19 }; 20 21 static bool __page_table_check_enabled __initdata = 22 IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED); 23 24 DEFINE_STATIC_KEY_TRUE(page_table_check_disabled); 25 EXPORT_SYMBOL(page_table_check_disabled); 26 27 static int __init early_page_table_check_param(char *buf) 28 { 29 return kstrtobool(buf, &__page_table_check_enabled); 30 } 31 32 early_param("page_table_check", early_page_table_check_param); 33 34 static bool __init need_page_table_check(void) 35 { 36 return __page_table_check_enabled; 37 } 38 39 static void __init init_page_table_check(void) 40 { 41 if (!__page_table_check_enabled) 42 return; 43 static_branch_disable(&page_table_check_disabled); 44 } 45 46 struct page_ext_operations page_table_check_ops = { 47 .size = sizeof(struct page_table_check), 48 .need = need_page_table_check, 49 .init = init_page_table_check, 50 .need_shared_flags = false, 51 }; 52 53 static struct page_table_check *get_page_table_check(struct page_ext *page_ext) 54 { 55 BUG_ON(!page_ext); 56 return page_ext_data(page_ext, &page_table_check_ops); 57 } 58 59 /* 60 * An entry is removed from the page table, decrement the counters for that page 61 * verify that it is of correct type and counters do not become negative. 62 */ 63 static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt) 64 { 65 struct page_ext_iter iter; 66 struct page_ext *page_ext; 67 struct page *page; 68 bool anon; 69 70 if (!pfn_valid(pfn)) 71 return; 72 73 page = pfn_to_page(pfn); 74 BUG_ON(PageSlab(page)); 75 anon = PageAnon(page); 76 77 rcu_read_lock(); 78 for_each_page_ext(page, pgcnt, page_ext, iter) { 79 struct page_table_check *ptc = get_page_table_check(page_ext); 80 81 if (anon) { 82 BUG_ON(atomic_read(&ptc->file_map_count)); 83 BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0); 84 } else { 85 BUG_ON(atomic_read(&ptc->anon_map_count)); 86 BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0); 87 } 88 } 89 rcu_read_unlock(); 90 } 91 92 /* 93 * A new entry is added to the page table, increment the counters for that page 94 * verify that it is of correct type and is not being mapped with a different 95 * type to a different process. 96 */ 97 static void page_table_check_set(unsigned long pfn, unsigned long pgcnt, 98 bool rw) 99 { 100 struct page_ext_iter iter; 101 struct page_ext *page_ext; 102 struct page *page; 103 bool anon; 104 105 if (!pfn_valid(pfn)) 106 return; 107 108 page = pfn_to_page(pfn); 109 BUG_ON(PageSlab(page)); 110 anon = PageAnon(page); 111 112 rcu_read_lock(); 113 for_each_page_ext(page, pgcnt, page_ext, iter) { 114 struct page_table_check *ptc = get_page_table_check(page_ext); 115 116 if (anon) { 117 BUG_ON(atomic_read(&ptc->file_map_count)); 118 BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw); 119 } else { 120 BUG_ON(atomic_read(&ptc->anon_map_count)); 121 BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0); 122 } 123 } 124 rcu_read_unlock(); 125 } 126 127 /* 128 * page is on free list, or is being allocated, verify that counters are zeroes 129 * crash if they are not. 130 */ 131 void __page_table_check_zero(struct page *page, unsigned int order) 132 { 133 struct page_ext_iter iter; 134 struct page_ext *page_ext; 135 136 BUG_ON(PageSlab(page)); 137 138 rcu_read_lock(); 139 for_each_page_ext(page, 1 << order, page_ext, iter) { 140 struct page_table_check *ptc = get_page_table_check(page_ext); 141 142 BUG_ON(atomic_read(&ptc->anon_map_count)); 143 BUG_ON(atomic_read(&ptc->file_map_count)); 144 } 145 rcu_read_unlock(); 146 } 147 148 void __page_table_check_pte_clear(struct mm_struct *mm, pte_t pte) 149 { 150 if (&init_mm == mm) 151 return; 152 153 if (pte_user_accessible_page(pte)) { 154 page_table_check_clear(pte_pfn(pte), PAGE_SIZE >> PAGE_SHIFT); 155 } 156 } 157 EXPORT_SYMBOL(__page_table_check_pte_clear); 158 159 void __page_table_check_pmd_clear(struct mm_struct *mm, pmd_t pmd) 160 { 161 if (&init_mm == mm) 162 return; 163 164 if (pmd_user_accessible_page(pmd)) { 165 page_table_check_clear(pmd_pfn(pmd), PMD_SIZE >> PAGE_SHIFT); 166 } 167 } 168 EXPORT_SYMBOL(__page_table_check_pmd_clear); 169 170 void __page_table_check_pud_clear(struct mm_struct *mm, pud_t pud) 171 { 172 if (&init_mm == mm) 173 return; 174 175 if (pud_user_accessible_page(pud)) { 176 page_table_check_clear(pud_pfn(pud), PUD_SIZE >> PAGE_SHIFT); 177 } 178 } 179 EXPORT_SYMBOL(__page_table_check_pud_clear); 180 181 /* Whether the swap entry cached writable information */ 182 static inline bool swap_cached_writable(swp_entry_t entry) 183 { 184 return is_writable_device_private_entry(entry) || 185 is_writable_migration_entry(entry); 186 } 187 188 static inline void page_table_check_pte_flags(pte_t pte) 189 { 190 if (pte_present(pte) && pte_uffd_wp(pte)) 191 WARN_ON_ONCE(pte_write(pte)); 192 else if (is_swap_pte(pte) && pte_swp_uffd_wp(pte)) 193 WARN_ON_ONCE(swap_cached_writable(pte_to_swp_entry(pte))); 194 } 195 196 void __page_table_check_ptes_set(struct mm_struct *mm, pte_t *ptep, pte_t pte, 197 unsigned int nr) 198 { 199 unsigned int i; 200 201 if (&init_mm == mm) 202 return; 203 204 page_table_check_pte_flags(pte); 205 206 for (i = 0; i < nr; i++) 207 __page_table_check_pte_clear(mm, ptep_get(ptep + i)); 208 if (pte_user_accessible_page(pte)) 209 page_table_check_set(pte_pfn(pte), nr, pte_write(pte)); 210 } 211 EXPORT_SYMBOL(__page_table_check_ptes_set); 212 213 static inline void page_table_check_pmd_flags(pmd_t pmd) 214 { 215 if (pmd_present(pmd) && pmd_uffd_wp(pmd)) 216 WARN_ON_ONCE(pmd_write(pmd)); 217 else if (is_swap_pmd(pmd) && pmd_swp_uffd_wp(pmd)) 218 WARN_ON_ONCE(swap_cached_writable(pmd_to_swp_entry(pmd))); 219 } 220 221 void __page_table_check_pmds_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd, 222 unsigned int nr) 223 { 224 unsigned long stride = PMD_SIZE >> PAGE_SHIFT; 225 unsigned int i; 226 227 if (&init_mm == mm) 228 return; 229 230 page_table_check_pmd_flags(pmd); 231 232 for (i = 0; i < nr; i++) 233 __page_table_check_pmd_clear(mm, *(pmdp + i)); 234 if (pmd_user_accessible_page(pmd)) 235 page_table_check_set(pmd_pfn(pmd), stride * nr, pmd_write(pmd)); 236 } 237 EXPORT_SYMBOL(__page_table_check_pmds_set); 238 239 void __page_table_check_puds_set(struct mm_struct *mm, pud_t *pudp, pud_t pud, 240 unsigned int nr) 241 { 242 unsigned long stride = PUD_SIZE >> PAGE_SHIFT; 243 unsigned int i; 244 245 if (&init_mm == mm) 246 return; 247 248 for (i = 0; i < nr; i++) 249 __page_table_check_pud_clear(mm, *(pudp + i)); 250 if (pud_user_accessible_page(pud)) 251 page_table_check_set(pud_pfn(pud), stride * nr, pud_write(pud)); 252 } 253 EXPORT_SYMBOL(__page_table_check_puds_set); 254 255 void __page_table_check_pte_clear_range(struct mm_struct *mm, 256 unsigned long addr, 257 pmd_t pmd) 258 { 259 if (&init_mm == mm) 260 return; 261 262 if (!pmd_bad(pmd) && !pmd_leaf(pmd)) { 263 pte_t *ptep = pte_offset_map(&pmd, addr); 264 unsigned long i; 265 266 if (WARN_ON(!ptep)) 267 return; 268 for (i = 0; i < PTRS_PER_PTE; i++) { 269 __page_table_check_pte_clear(mm, ptep_get(ptep)); 270 addr += PAGE_SIZE; 271 ptep++; 272 } 273 pte_unmap(ptep - PTRS_PER_PTE); 274 } 275 } 276