mm/mprotect.c

   1 /*
   2  *  mm/mprotect.c
   3  *
   4  *  (C) Copyright 1994 Linus Torvalds
   5  *  (C) Copyright 2002 Christoph Hellwig
   6  *
   7  *  Address space accounting code       <alan@lxorguk.ukuu.org.uk>
   8  *  (C) Copyright 2002 Red Hat Inc, All Rights Reserved
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/hugetlb.h>
  13 #include <linux/shm.h>
  14 #include <linux/mman.h>
  15 #include <linux/fs.h>
  16 #include <linux/highmem.h>
  17 #include <linux/security.h>
  18 #include <linux/mempolicy.h>
  19 #include <linux/personality.h>
  20 #include <linux/syscalls.h>
  21 #include <linux/swap.h>
  22 #include <linux/swapops.h>
  23 #include <linux/mmu_notifier.h>
  24 #include <linux/migrate.h>
  25 #include <linux/perf_event.h>
  26 #include <linux/ksm.h>
  27 #include <asm/uaccess.h>
  28 #include <asm/pgtable.h>
  29 #include <asm/cacheflush.h>
  30 #include <asm/tlbflush.h>
  31
  32 #include "internal.h"
  33
  34 /*
  35  * For a prot_numa update we only hold mmap_sem for read so there is a
  36  * potential race with faulting where a pmd was temporarily none. This
  37  * function checks for a transhuge pmd under the appropriate lock. It
  38  * returns a pte if it was successfully locked or NULL if it raced with
  39  * a transhuge insertion.
  40  */
  41 static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
  42                         unsigned long addr, int prot_numa, spinlock_t **ptl)
  43 {
  44         pte_t *pte;
  45         spinlock_t *pmdl;
  46
  47         /* !prot_numa is protected by mmap_sem held for write */
  48         if (!prot_numa)
  49                 return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  50
  51         pmdl = pmd_lock(vma->vm_mm, pmd);
  52         if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
  53                 spin_unlock(pmdl);
  54                 return NULL;
  55         }
  56
  57         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  58         spin_unlock(pmdl);
  59         return pte;
  60 }
  61
  62 static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  63                 unsigned long addr, unsigned long end, pgprot_t newprot,
  64                 int dirty_accountable, int prot_numa)
  65 {
  66         struct mm_struct *mm = vma->vm_mm;
  67         pte_t *pte, oldpte;
  68         spinlock_t *ptl;
  69         unsigned long pages = 0;
  70
  71         pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
  72         if (!pte)
  73                 return 0;
  74
  75         flush_tlb_batched_pending(vma->vm_mm);
  76         arch_enter_lazy_mmu_mode();
  77         do {
  78                 oldpte = *pte;
  79                 if (pte_present(oldpte)) {
  80                         pte_t ptent;
  81                         bool preserve_write = prot_numa && pte_write(oldpte);
  82
  83                         /*
  84                          * Avoid trapping faults against the zero or KSM
  85                          * pages. See similar comment in change_huge_pmd.
  86                          */
  87                         if (prot_numa) {
  88                                 struct page *page;
  89
  90                                 page = vm_normal_page(vma, addr, oldpte);
  91                                 if (!page || PageKsm(page))
  92                                         continue;
  93
  94                                 /* Avoid TLB flush if possible */
  95                                 if (pte_protnone(oldpte))
  96                                         continue;
  97                         }
  98
  99                         ptent = ptep_modify_prot_start(mm, addr, pte);
 100                         ptent = pte_modify(ptent, newprot);
 101                         if (preserve_write)
 102                                 ptent = pte_mkwrite(ptent);
 103
 104                         /* Avoid taking write faults for known dirty pages */
 105                         if (dirty_accountable && pte_dirty(ptent) &&
 106                                         (pte_soft_dirty(ptent) ||
 107                                          !(vma->vm_flags & VM_SOFTDIRTY))) {
 108                                 ptent = pte_mkwrite(ptent);
 109                         }
 110                         ptep_modify_prot_commit(mm, addr, pte, ptent);
 111                         pages++;
 112                 } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 113                         swp_entry_t entry = pte_to_swp_entry(oldpte);
 114
 115                         if (is_write_migration_entry(entry)) {
 116                                 pte_t newpte;
 117                                 /*
 118                                  * A protection check is difficult so
 119                                  * just be safe and disable write
 120                                  */
 121                                 make_migration_entry_read(&entry);
 122                                 newpte = swp_entry_to_pte(entry);
 123                                 if (pte_swp_soft_dirty(oldpte))
 124                                         newpte = pte_swp_mksoft_dirty(newpte);
 125                                 set_pte_at(mm, addr, pte, newpte);
 126
 127                                 pages++;
 128                         }
 129                 }
 130         } while (pte++, addr += PAGE_SIZE, addr != end);
 131         arch_leave_lazy_mmu_mode();
 132         pte_unmap_unlock(pte - 1, ptl);
 133
 134         return pages;
 135 }
 136
 137 static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 138                 pud_t *pud, unsigned long addr, unsigned long end,
 139                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 140 {
 141         pmd_t *pmd;
 142         struct mm_struct *mm = vma->vm_mm;
 143         unsigned long next;
 144         unsigned long pages = 0;
 145         unsigned long nr_huge_updates = 0;
 146         unsigned long mni_start = 0;
 147
 148         pmd = pmd_offset(pud, addr);
 149         do {
 150                 unsigned long this_pages;
 151
 152                 next = pmd_addr_end(addr, end);
 153                 if (!pmd_trans_huge(*pmd) && pmd_none_or_clear_bad(pmd))
 154                         continue;
 155
 156                 /* invoke the mmu notifier if the pmd is populated */
 157                 if (!mni_start) {
 158                         mni_start = addr;
 159                         mmu_notifier_invalidate_range_start(mm, mni_start, end);
 160                 }
 161
 162                 if (pmd_trans_huge(*pmd)) {
 163                         if (next - addr != HPAGE_PMD_SIZE)
 164                                 split_huge_page_pmd(vma, addr, pmd);
 165                         else {
 166                                 int nr_ptes = change_huge_pmd(vma, pmd, addr,
 167                                                 newprot, prot_numa);
 168
 169                                 if (nr_ptes) {
 170                                         if (nr_ptes == HPAGE_PMD_NR) {
 171                                                 pages += HPAGE_PMD_NR;
 172                                                 nr_huge_updates++;
 173                                         }
 174
 175                                         /* huge pmd was handled */
 176                                         continue;
 177                                 }
 178                         }
 179                         /* fall through, the trans huge pmd just split */
 180                 }
 181                 this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 182                                  dirty_accountable, prot_numa);
 183                 pages += this_pages;
 184         } while (pmd++, addr = next, addr != end);
 185
 186         if (mni_start)
 187                 mmu_notifier_invalidate_range_end(mm, mni_start, end);
 188
 189         if (nr_huge_updates)
 190                 count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 191         return pages;
 192 }
 193
 194 static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 195                 pgd_t *pgd, unsigned long addr, unsigned long end,
 196                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 197 {
 198         pud_t *pud;
 199         unsigned long next;
 200         unsigned long pages = 0;
 201
 202         pud = pud_offset(pgd, addr);
 203         do {
 204                 next = pud_addr_end(addr, end);
 205                 if (pud_none_or_clear_bad(pud))
 206                         continue;
 207                 pages += change_pmd_range(vma, pud, addr, next, newprot,
 208                                  dirty_accountable, prot_numa);
 209         } while (pud++, addr = next, addr != end);
 210
 211         return pages;
 212 }
 213
 214 static unsigned long change_protection_range(struct vm_area_struct *vma,
 215                 unsigned long addr, unsigned long end, pgprot_t newprot,
 216                 int dirty_accountable, int prot_numa)
 217 {
 218         struct mm_struct *mm = vma->vm_mm;
 219         pgd_t *pgd;
 220         unsigned long next;
 221         unsigned long start = addr;
 222         unsigned long pages = 0;
 223
 224         BUG_ON(addr >= end);
 225         pgd = pgd_offset(mm, addr);
 226         flush_cache_range(vma, addr, end);
 227         set_tlb_flush_pending(mm);
 228         do {
 229                 next = pgd_addr_end(addr, end);
 230                 if (pgd_none_or_clear_bad(pgd))
 231                         continue;
 232                 pages += change_pud_range(vma, pgd, addr, next, newprot,
 233                                  dirty_accountable, prot_numa);
 234         } while (pgd++, addr = next, addr != end);
 235
 236         /* Only flush the TLB if we actually modified any entries: */
 237         if (pages)
 238                 flush_tlb_range(vma, start, end);
 239         clear_tlb_flush_pending(mm);
 240
 241         return pages;
 242 }
 243
 244 unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 245                        unsigned long end, pgprot_t newprot,
 246                        int dirty_accountable, int prot_numa)
 247 {
 248         unsigned long pages;
 249
 250         if (is_vm_hugetlb_page(vma))
 251                 pages = hugetlb_change_protection(vma, start, end, newprot);
 252         else
 253                 pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 254
 255         return pages;
 256 }
 257
 258 static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
 259                                unsigned long next, struct mm_walk *walk)
 260 {
 261         return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
 262                 0 : -EACCES;
 263 }
 264
 265 static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
 266                                    unsigned long addr, unsigned long next,
 267                                    struct mm_walk *walk)
 268 {
 269         return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
 270                 0 : -EACCES;
 271 }
 272
 273 static int prot_none_test(unsigned long addr, unsigned long next,
 274                           struct mm_walk *walk)
 275 {
 276         return 0;
 277 }
 278
 279 static int prot_none_walk(struct vm_area_struct *vma, unsigned long start,
 280                            unsigned long end, unsigned long newflags)
 281 {
 282         pgprot_t new_pgprot = vm_get_page_prot(newflags);
 283         struct mm_walk prot_none_walk = {
 284                 .pte_entry = prot_none_pte_entry,
 285                 .hugetlb_entry = prot_none_hugetlb_entry,
 286                 .test_walk = prot_none_test,
 287                 .mm = current->mm,
 288                 .private = &new_pgprot,
 289         };
 290
 291         return walk_page_range(start, end, &prot_none_walk);
 292 }
 293
 294 int
 295 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 296         unsigned long start, unsigned long end, unsigned long newflags)
 297 {
 298         struct mm_struct *mm = vma->vm_mm;
 299         unsigned long oldflags = vma->vm_flags;
 300         long nrpages = (end - start) >> PAGE_SHIFT;
 301         unsigned long charged = 0;
 302         pgoff_t pgoff;
 303         int error;
 304         int dirty_accountable = 0;
 305
 306         if (newflags == oldflags) {
 307                 *pprev = vma;
 308                 return 0;
 309         }
 310
 311         /*
 312          * Do PROT_NONE PFN permission checks here when we can still
 313          * bail out without undoing a lot of state. This is a rather
 314          * uncommon case, so doesn't need to be very optimized.
 315          */
 316         if (arch_has_pfn_modify_check() &&
 317             (vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
 318             (newflags & (VM_READ|VM_WRITE|VM_EXEC)) == 0) {
 319                 error = prot_none_walk(vma, start, end, newflags);
 320                 if (error)
 321                         return error;
 322         }
 323
 324         /*
 325          * If we make a private mapping writable we increase our commit;
 326          * but (without finer accounting) cannot reduce our commit if we
 327          * make it unwritable again. hugetlb mapping were accounted for
 328          * even if read-only so there is no need to account for them here
 329          */
 330         if (newflags & VM_WRITE) {
 331                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 332                                                 VM_SHARED|VM_NORESERVE))) {
 333                         charged = nrpages;
 334                         if (security_vm_enough_memory_mm(mm, charged))
 335                                 return -ENOMEM;
 336                         newflags |= VM_ACCOUNT;
 337                 }
 338         }
 339
 340         /*
 341          * First try to merge with previous and/or next vma.
 342          */
 343         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 344         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 345                            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 346                            vma->vm_userfaultfd_ctx);
 347         if (*pprev) {
 348                 vma = *pprev;
 349                 goto success;
 350         }
 351
 352         *pprev = vma;
 353
 354         if (start != vma->vm_start) {
 355                 error = split_vma(mm, vma, start, 1);
 356                 if (error)
 357                         goto fail;
 358         }
 359
 360         if (end != vma->vm_end) {
 361                 error = split_vma(mm, vma, end, 0);
 362                 if (error)
 363                         goto fail;
 364         }
 365
 366 success:
 367         /*
 368          * vm_flags and vm_page_prot are protected by the mmap_sem
 369          * held in write mode.
 370          */
 371         vma->vm_flags = newflags;
 372         dirty_accountable = vma_wants_writenotify(vma);
 373         vma_set_page_prot(vma);
 374
 375         change_protection(vma, start, end, vma->vm_page_prot,
 376                           dirty_accountable, 0);
 377
 378         /*
 379          * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 380          * fault on access.
 381          */
 382         if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 383                         (newflags & VM_WRITE)) {
 384                 populate_vma_page_range(vma, start, end, NULL);
 385         }
 386
 387         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 388         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 389         perf_event_mmap(vma);
 390         return 0;
 391
 392 fail:
 393         vm_unacct_memory(charged);
 394         return error;
 395 }
 396
 397 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 398                 unsigned long, prot)
 399 {
 400         unsigned long vm_flags, nstart, end, tmp, reqprot;
 401         struct vm_area_struct *vma, *prev;
 402         int error = -EINVAL;
 403         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 404         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 405         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 406                 return -EINVAL;
 407
 408         if (start & ~PAGE_MASK)
 409                 return -EINVAL;
 410         if (!len)
 411                 return 0;
 412         len = PAGE_ALIGN(len);
 413         end = start + len;
 414         if (end <= start)
 415                 return -ENOMEM;
 416         if (!arch_validate_prot(prot))
 417                 return -EINVAL;
 418
 419         reqprot = prot;
 420         /*
 421          * Does the application expect PROT_READ to imply PROT_EXEC:
 422          */
 423         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 424                 prot |= PROT_EXEC;
 425
 426         vm_flags = calc_vm_prot_bits(prot);
 427
 428         down_write(&current->mm->mmap_sem);
 429
 430         vma = find_vma(current->mm, start);
 431         error = -ENOMEM;
 432         if (!vma)
 433                 goto out;
 434         prev = vma->vm_prev;
 435         if (unlikely(grows & PROT_GROWSDOWN)) {
 436                 if (vma->vm_start >= end)
 437                         goto out;
 438                 start = vma->vm_start;
 439                 error = -EINVAL;
 440                 if (!(vma->vm_flags & VM_GROWSDOWN))
 441                         goto out;
 442         } else {
 443                 if (vma->vm_start > start)
 444                         goto out;
 445                 if (unlikely(grows & PROT_GROWSUP)) {
 446                         end = vma->vm_end;
 447                         error = -EINVAL;
 448                         if (!(vma->vm_flags & VM_GROWSUP))
 449                                 goto out;
 450                 }
 451         }
 452         if (start > vma->vm_start)
 453                 prev = vma;
 454
 455         for (nstart = start ; ; ) {
 456                 unsigned long newflags;
 457
 458                 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 459
 460                 newflags = vm_flags;
 461                 newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 462
 463                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 464                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 465                         error = -EACCES;
 466                         goto out;
 467                 }
 468
 469                 error = security_file_mprotect(vma, reqprot, prot);
 470                 if (error)
 471                         goto out;
 472
 473                 tmp = vma->vm_end;
 474                 if (tmp > end)
 475                         tmp = end;
 476                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 477                 if (error)
 478                         goto out;
 479                 nstart = tmp;
 480
 481                 if (nstart < prev->vm_end)
 482                         nstart = prev->vm_end;
 483                 if (nstart >= end)
 484                         goto out;
 485
 486                 vma = prev->vm_next;
 487                 if (!vma || vma->vm_start != nstart) {
 488                         error = -ENOMEM;
 489                         goto out;
 490                 }
 491         }
 492 out:
 493         up_write(&current->mm->mmap_sem);
 494         return error;
 495 }