mm/page_table_check.c

   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 {
  26         return strtobool(buf, &__page_table_check_enabled);
  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 /*
  56  * An enty is removed from the page table, decrement the counters for that page
  57  * verify that it is of correct type and counters do not become negative.
  58  */
  59 static void page_table_check_clear(struct mm_struct *mm, unsigned long addr,
  60                                    unsigned long pfn, unsigned long pgcnt)
  61 {
  62         struct page_ext *page_ext;
  63         struct page *page;
  64         unsigned long i;
  65         bool anon;
  66
  67         if (!pfn_valid(pfn))
  68                 return;
  69
  70         page = pfn_to_page(pfn);
  71         page_ext = lookup_page_ext(page);
  72         anon = PageAnon(page);
  73
  74         for (i = 0; i < pgcnt; i++) {
  75                 struct page_table_check *ptc = get_page_table_check(page_ext);
  76
  77                 if (anon) {
  78                         BUG_ON(atomic_read(&ptc->file_map_count));
  79                         BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0);
  80                 } else {
  81                         BUG_ON(atomic_read(&ptc->anon_map_count));
  82                         BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
  83                 }
  84                 page_ext = page_ext_next(page_ext);
  85         }
  86 }
  87
  88 /*
  89  * A new enty is added to the page table, increment the counters for that page
  90  * verify that it is of correct type and is not being mapped with a different
  91  * type to a different process.
  92  */
  93 static void page_table_check_set(struct mm_struct *mm, unsigned long addr,
  94                                  unsigned long pfn, unsigned long pgcnt,
  95                                  bool rw)
  96 {
  97         struct page_ext *page_ext;
  98         struct page *page;
  99         unsigned long i;
 100         bool anon;
 101
 102         if (!pfn_valid(pfn))
 103                 return;
 104
 105         page = pfn_to_page(pfn);
 106         page_ext = lookup_page_ext(page);
 107         anon = PageAnon(page);
 108
 109         for (i = 0; i < pgcnt; i++) {
 110                 struct page_table_check *ptc = get_page_table_check(page_ext);
 111
 112                 if (anon) {
 113                         BUG_ON(atomic_read(&ptc->file_map_count));
 114                         BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);
 115                 } else {
 116                         BUG_ON(atomic_read(&ptc->anon_map_count));
 117                         BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0);
 118                 }
 119                 page_ext = page_ext_next(page_ext);
 120         }
 121 }
 122
 123 /*
 124  * page is on free list, or is being allocated, verify that counters are zeroes
 125  * crash if they are not.
 126  */
 127 void __page_table_check_zero(struct page *page, unsigned int order)
 128 {
 129         struct page_ext *page_ext = lookup_page_ext(page);
 130         unsigned long i;
 131
 132         BUG_ON(!page_ext);
 133         for (i = 0; i < (1ul << order); i++) {
 134                 struct page_table_check *ptc = get_page_table_check(page_ext);
 135
 136                 BUG_ON(atomic_read(&ptc->anon_map_count));
 137                 BUG_ON(atomic_read(&ptc->file_map_count));
 138                 page_ext = page_ext_next(page_ext);
 139         }
 140 }
 141
 142 void __page_table_check_pte_clear(struct mm_struct *mm, unsigned long addr,
 143                                   pte_t pte)
 144 {
 145         if (&init_mm == mm)
 146                 return;
 147
 148         if (pte_user_accessible_page(pte)) {
 149                 page_table_check_clear(mm, addr, pte_pfn(pte),
 150                                        PAGE_SIZE >> PAGE_SHIFT);
 151         }
 152 }
 153 EXPORT_SYMBOL(__page_table_check_pte_clear);
 154
 155 void __page_table_check_pmd_clear(struct mm_struct *mm, unsigned long addr,
 156                                   pmd_t pmd)
 157 {
 158         if (&init_mm == mm)
 159                 return;
 160
 161         if (pmd_user_accessible_page(pmd)) {
 162                 page_table_check_clear(mm, addr, pmd_pfn(pmd),
 163                                        PMD_SIZE >> PAGE_SHIFT);
 164         }
 165 }
 166 EXPORT_SYMBOL(__page_table_check_pmd_clear);
 167
 168 void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr,
 169                                   pud_t pud)
 170 {
 171         if (&init_mm == mm)
 172                 return;
 173
 174         if (pud_user_accessible_page(pud)) {
 175                 page_table_check_clear(mm, addr, pud_pfn(pud),
 176                                        PUD_SIZE >> PAGE_SHIFT);
 177         }
 178 }
 179 EXPORT_SYMBOL(__page_table_check_pud_clear);
 180
 181 void __page_table_check_pte_set(struct mm_struct *mm, unsigned long addr,
 182                                 pte_t *ptep, pte_t pte)
 183 {
 184         if (&init_mm == mm)
 185                 return;
 186
 187         __page_table_check_pte_clear(mm, addr, *ptep);
 188         if (pte_user_accessible_page(pte)) {
 189                 page_table_check_set(mm, addr, pte_pfn(pte),
 190                                      PAGE_SIZE >> PAGE_SHIFT,
 191                                      pte_write(pte));
 192         }
 193 }
 194 EXPORT_SYMBOL(__page_table_check_pte_set);
 195
 196 void __page_table_check_pmd_set(struct mm_struct *mm, unsigned long addr,
 197                                 pmd_t *pmdp, pmd_t pmd)
 198 {
 199         if (&init_mm == mm)
 200                 return;
 201
 202         __page_table_check_pmd_clear(mm, addr, *pmdp);
 203         if (pmd_user_accessible_page(pmd)) {
 204                 page_table_check_set(mm, addr, pmd_pfn(pmd),
 205                                      PMD_SIZE >> PAGE_SHIFT,
 206                                      pmd_write(pmd));
 207         }
 208 }
 209 EXPORT_SYMBOL(__page_table_check_pmd_set);
 210
 211 void __page_table_check_pud_set(struct mm_struct *mm, unsigned long addr,
 212                                 pud_t *pudp, pud_t pud)
 213 {
 214         if (&init_mm == mm)
 215                 return;
 216
 217         __page_table_check_pud_clear(mm, addr, *pudp);
 218         if (pud_user_accessible_page(pud)) {
 219                 page_table_check_set(mm, addr, pud_pfn(pud),
 220                                      PUD_SIZE >> PAGE_SHIFT,
 221                                      pud_write(pud));
 222         }
 223 }
 224 EXPORT_SYMBOL(__page_table_check_pud_set);
 225
 226 void __page_table_check_pte_clear_range(struct mm_struct *mm,
 227                                         unsigned long addr,
 228                                         pmd_t pmd)
 229 {
 230         if (&init_mm == mm)
 231                 return;
 232
 233         if (!pmd_bad(pmd) && !pmd_leaf(pmd)) {
 234                 pte_t *ptep = pte_offset_map(&pmd, addr);
 235                 unsigned long i;
 236
 237                 for (i = 0; i < PTRS_PER_PTE; i++) {
 238                         __page_table_check_pte_clear(mm, addr, *ptep);
 239                         addr += PAGE_SIZE;
 240                         ptep++;
 241                 }
 242                 pte_unmap(ptep - PTRS_PER_PTE);
 243         }
 244 }