mm/mprotect.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  mm/mprotect.c
   4  *
   5  *  (C) Copyright 1994 Linus Torvalds
   6  *  (C) Copyright 2002 Christoph Hellwig
   7  *
   8  *  Address space accounting code       <alan@lxorguk.ukuu.org.uk>
   9  *  (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  10  */
  11
  12 #include <linux/mm.h>
  13 #include <linux/hugetlb.h>
  14 #include <linux/shm.h>
  15 #include <linux/mman.h>
  16 #include <linux/fs.h>
  17 #include <linux/highmem.h>
  18 #include <linux/security.h>
  19 #include <linux/mempolicy.h>
  20 #include <linux/personality.h>
  21 #include <linux/syscalls.h>
  22 #include <linux/swap.h>
  23 #include <linux/swapops.h>
  24 #include <linux/mmu_notifier.h>
  25 #include <linux/migrate.h>
  26 #include <linux/perf_event.h>
  27 #include <linux/pkeys.h>
  28 #include <linux/ksm.h>
  29 #include <linux/uaccess.h>
  30 #include <linux/mm_inline.h>
  31 #include <asm/pgtable.h>
  32 #include <asm/cacheflush.h>
  33 #include <asm/mmu_context.h>
  34 #include <asm/tlbflush.h>
  35
  36 #include "internal.h"
  37
  38 static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  39                 unsigned long addr, unsigned long end, pgprot_t newprot,
  40                 int dirty_accountable, int prot_numa)
  41 {
  42         pte_t *pte, oldpte;
  43         spinlock_t *ptl;
  44         unsigned long pages = 0;
  45         int target_node = NUMA_NO_NODE;
  46
  47         /*
  48          * Can be called with only the mmap_sem for reading by
  49          * prot_numa so we must check the pmd isn't constantly
  50          * changing from under us from pmd_none to pmd_trans_huge
  51          * and/or the other way around.
  52          */
  53         if (pmd_trans_unstable(pmd))
  54                 return 0;
  55
  56         /*
  57          * The pmd points to a regular pte so the pmd can't change
  58          * from under us even if the mmap_sem is only hold for
  59          * reading.
  60          */
  61         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
  62
  63         /* Get target node for single threaded private VMAs */
  64         if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
  65             atomic_read(&vma->vm_mm->mm_users) == 1)
  66                 target_node = numa_node_id();
  67
  68         flush_tlb_batched_pending(vma->vm_mm);
  69         arch_enter_lazy_mmu_mode();
  70         do {
  71                 oldpte = *pte;
  72                 if (pte_present(oldpte)) {
  73                         pte_t ptent;
  74                         bool preserve_write = prot_numa && pte_write(oldpte);
  75
  76                         /*
  77                          * Avoid trapping faults against the zero or KSM
  78                          * pages. See similar comment in change_huge_pmd.
  79                          */
  80                         if (prot_numa) {
  81                                 struct page *page;
  82
  83                                 page = vm_normal_page(vma, addr, oldpte);
  84                                 if (!page || PageKsm(page))
  85                                         continue;
  86
  87                                 /* Also skip shared copy-on-write pages */
  88                                 if (is_cow_mapping(vma->vm_flags) &&
  89                                     page_mapcount(page) != 1)
  90                                         continue;
  91
  92                                 /*
  93                                  * While migration can move some dirty pages,
  94                                  * it cannot move them all from MIGRATE_ASYNC
  95                                  * context.
  96                                  */
  97                                 if (page_is_file_cache(page) && PageDirty(page))
  98                                         continue;
  99
 100                                 /* Avoid TLB flush if possible */
 101                                 if (pte_protnone(oldpte))
 102                                         continue;
 103
 104                                 /*
 105                                  * Don't mess with PTEs if page is already on the node
 106                                  * a single-threaded process is running on.
 107                                  */
 108                                 if (target_node == page_to_nid(page))
 109                                         continue;
 110                         }
 111
 112                         oldpte = ptep_modify_prot_start(vma, addr, pte);
 113                         ptent = pte_modify(oldpte, newprot);
 114                         if (preserve_write)
 115                                 ptent = pte_mk_savedwrite(ptent);
 116
 117                         /* Avoid taking write faults for known dirty pages */
 118                         if (dirty_accountable && pte_dirty(ptent) &&
 119                                         (pte_soft_dirty(ptent) ||
 120                                          !(vma->vm_flags & VM_SOFTDIRTY))) {
 121                                 ptent = pte_mkwrite(ptent);
 122                         }
 123                         ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
 124                         pages++;
 125                 } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 126                         swp_entry_t entry = pte_to_swp_entry(oldpte);
 127
 128                         if (is_write_migration_entry(entry)) {
 129                                 pte_t newpte;
 130                                 /*
 131                                  * A protection check is difficult so
 132                                  * just be safe and disable write
 133                                  */
 134                                 make_migration_entry_read(&entry);
 135                                 newpte = swp_entry_to_pte(entry);
 136                                 if (pte_swp_soft_dirty(oldpte))
 137                                         newpte = pte_swp_mksoft_dirty(newpte);
 138                                 set_pte_at(vma->vm_mm, addr, pte, newpte);
 139
 140                                 pages++;
 141                         }
 142
 143                         if (is_write_device_private_entry(entry)) {
 144                                 pte_t newpte;
 145
 146                                 /*
 147                                  * We do not preserve soft-dirtiness. See
 148                                  * copy_one_pte() for explanation.
 149                                  */
 150                                 make_device_private_entry_read(&entry);
 151                                 newpte = swp_entry_to_pte(entry);
 152                                 set_pte_at(vma->vm_mm, addr, pte, newpte);
 153
 154                                 pages++;
 155                         }
 156                 }
 157         } while (pte++, addr += PAGE_SIZE, addr != end);
 158         arch_leave_lazy_mmu_mode();
 159         pte_unmap_unlock(pte - 1, ptl);
 160
 161         return pages;
 162 }
 163
 164 static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 165                 pud_t *pud, unsigned long addr, unsigned long end,
 166                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 167 {
 168         pmd_t *pmd;
 169         unsigned long next;
 170         unsigned long pages = 0;
 171         unsigned long nr_huge_updates = 0;
 172         struct mmu_notifier_range range;
 173
 174         range.start = 0;
 175
 176         pmd = pmd_offset(pud, addr);
 177         do {
 178                 unsigned long this_pages;
 179
 180                 next = pmd_addr_end(addr, end);
 181                 if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
 182                                 && pmd_none_or_clear_bad(pmd))
 183                         goto next;
 184
 185                 /* invoke the mmu notifier if the pmd is populated */
 186                 if (!range.start) {
 187                         mmu_notifier_range_init(&range,
 188                                 MMU_NOTIFY_PROTECTION_VMA, 0,
 189                                 vma, vma->vm_mm, addr, end);
 190                         mmu_notifier_invalidate_range_start(&range);
 191                 }
 192
 193                 if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
 194                         if (next - addr != HPAGE_PMD_SIZE) {
 195                                 __split_huge_pmd(vma, pmd, addr, false, NULL);
 196                         } else {
 197                                 int nr_ptes = change_huge_pmd(vma, pmd, addr,
 198                                                 newprot, prot_numa);
 199
 200                                 if (nr_ptes) {
 201                                         if (nr_ptes == HPAGE_PMD_NR) {
 202                                                 pages += HPAGE_PMD_NR;
 203                                                 nr_huge_updates++;
 204                                         }
 205
 206                                         /* huge pmd was handled */
 207                                         goto next;
 208                                 }
 209                         }
 210                         /* fall through, the trans huge pmd just split */
 211                 }
 212                 this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 213                                  dirty_accountable, prot_numa);
 214                 pages += this_pages;
 215 next:
 216                 cond_resched();
 217         } while (pmd++, addr = next, addr != end);
 218
 219         if (range.start)
 220                 mmu_notifier_invalidate_range_end(&range);
 221
 222         if (nr_huge_updates)
 223                 count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 224         return pages;
 225 }
 226
 227 static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 228                 p4d_t *p4d, unsigned long addr, unsigned long end,
 229                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 230 {
 231         pud_t *pud;
 232         unsigned long next;
 233         unsigned long pages = 0;
 234
 235         pud = pud_offset(p4d, addr);
 236         do {
 237                 next = pud_addr_end(addr, end);
 238                 if (pud_none_or_clear_bad(pud))
 239                         continue;
 240                 pages += change_pmd_range(vma, pud, addr, next, newprot,
 241                                  dirty_accountable, prot_numa);
 242         } while (pud++, addr = next, addr != end);
 243
 244         return pages;
 245 }
 246
 247 static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
 248                 pgd_t *pgd, unsigned long addr, unsigned long end,
 249                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 250 {
 251         p4d_t *p4d;
 252         unsigned long next;
 253         unsigned long pages = 0;
 254
 255         p4d = p4d_offset(pgd, addr);
 256         do {
 257                 next = p4d_addr_end(addr, end);
 258                 if (p4d_none_or_clear_bad(p4d))
 259                         continue;
 260                 pages += change_pud_range(vma, p4d, addr, next, newprot,
 261                                  dirty_accountable, prot_numa);
 262         } while (p4d++, addr = next, addr != end);
 263
 264         return pages;
 265 }
 266
 267 static unsigned long change_protection_range(struct vm_area_struct *vma,
 268                 unsigned long addr, unsigned long end, pgprot_t newprot,
 269                 int dirty_accountable, int prot_numa)
 270 {
 271         struct mm_struct *mm = vma->vm_mm;
 272         pgd_t *pgd;
 273         unsigned long next;
 274         unsigned long start = addr;
 275         unsigned long pages = 0;
 276
 277         BUG_ON(addr >= end);
 278         pgd = pgd_offset(mm, addr);
 279         flush_cache_range(vma, addr, end);
 280         inc_tlb_flush_pending(mm);
 281         do {
 282                 next = pgd_addr_end(addr, end);
 283                 if (pgd_none_or_clear_bad(pgd))
 284                         continue;
 285                 pages += change_p4d_range(vma, pgd, addr, next, newprot,
 286                                  dirty_accountable, prot_numa);
 287         } while (pgd++, addr = next, addr != end);
 288
 289         /* Only flush the TLB if we actually modified any entries: */
 290         if (pages)
 291                 flush_tlb_range(vma, start, end);
 292         dec_tlb_flush_pending(mm);
 293
 294         return pages;
 295 }
 296
 297 unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 298                        unsigned long end, pgprot_t newprot,
 299                        int dirty_accountable, int prot_numa)
 300 {
 301         unsigned long pages;
 302
 303         if (is_vm_hugetlb_page(vma))
 304                 pages = hugetlb_change_protection(vma, start, end, newprot);
 305         else
 306                 pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 307
 308         return pages;
 309 }
 310
 311 static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
 312                                unsigned long next, struct mm_walk *walk)
 313 {
 314         return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
 315                 0 : -EACCES;
 316 }
 317
 318 static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
 319                                    unsigned long addr, unsigned long next,
 320                                    struct mm_walk *walk)
 321 {
 322         return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
 323                 0 : -EACCES;
 324 }
 325
 326 static int prot_none_test(unsigned long addr, unsigned long next,
 327                           struct mm_walk *walk)
 328 {
 329         return 0;
 330 }
 331
 332 static int prot_none_walk(struct vm_area_struct *vma, unsigned long start,
 333                            unsigned long end, unsigned long newflags)
 334 {
 335         pgprot_t new_pgprot = vm_get_page_prot(newflags);
 336         struct mm_walk prot_none_walk = {
 337                 .pte_entry = prot_none_pte_entry,
 338                 .hugetlb_entry = prot_none_hugetlb_entry,
 339                 .test_walk = prot_none_test,
 340                 .mm = current->mm,
 341                 .private = &new_pgprot,
 342         };
 343
 344         return walk_page_range(start, end, &prot_none_walk);
 345 }
 346
 347 int
 348 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 349         unsigned long start, unsigned long end, unsigned long newflags)
 350 {
 351         struct mm_struct *mm = vma->vm_mm;
 352         unsigned long oldflags = vma->vm_flags;
 353         long nrpages = (end - start) >> PAGE_SHIFT;
 354         unsigned long charged = 0;
 355         pgoff_t pgoff;
 356         int error;
 357         int dirty_accountable = 0;
 358
 359         if (newflags == oldflags) {
 360                 *pprev = vma;
 361                 return 0;
 362         }
 363
 364         /*
 365          * Do PROT_NONE PFN permission checks here when we can still
 366          * bail out without undoing a lot of state. This is a rather
 367          * uncommon case, so doesn't need to be very optimized.
 368          */
 369         if (arch_has_pfn_modify_check() &&
 370             (vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
 371             (newflags & (VM_READ|VM_WRITE|VM_EXEC)) == 0) {
 372                 error = prot_none_walk(vma, start, end, newflags);
 373                 if (error)
 374                         return error;
 375         }
 376
 377         /*
 378          * If we make a private mapping writable we increase our commit;
 379          * but (without finer accounting) cannot reduce our commit if we
 380          * make it unwritable again. hugetlb mapping were accounted for
 381          * even if read-only so there is no need to account for them here
 382          */
 383         if (newflags & VM_WRITE) {
 384                 /* Check space limits when area turns into data. */
 385                 if (!may_expand_vm(mm, newflags, nrpages) &&
 386                                 may_expand_vm(mm, oldflags, nrpages))
 387                         return -ENOMEM;
 388                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 389                                                 VM_SHARED|VM_NORESERVE))) {
 390                         charged = nrpages;
 391                         if (security_vm_enough_memory_mm(mm, charged))
 392                                 return -ENOMEM;
 393                         newflags |= VM_ACCOUNT;
 394                 }
 395         }
 396
 397         /*
 398          * First try to merge with previous and/or next vma.
 399          */
 400         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 401         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 402                            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 403                            vma->vm_userfaultfd_ctx);
 404         if (*pprev) {
 405                 vma = *pprev;
 406                 VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
 407                 goto success;
 408         }
 409
 410         *pprev = vma;
 411
 412         if (start != vma->vm_start) {
 413                 error = split_vma(mm, vma, start, 1);
 414                 if (error)
 415                         goto fail;
 416         }
 417
 418         if (end != vma->vm_end) {
 419                 error = split_vma(mm, vma, end, 0);
 420                 if (error)
 421                         goto fail;
 422         }
 423
 424 success:
 425         /*
 426          * vm_flags and vm_page_prot are protected by the mmap_sem
 427          * held in write mode.
 428          */
 429         vma->vm_flags = newflags;
 430         dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
 431         vma_set_page_prot(vma);
 432
 433         change_protection(vma, start, end, vma->vm_page_prot,
 434                           dirty_accountable, 0);
 435
 436         /*
 437          * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 438          * fault on access.
 439          */
 440         if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 441                         (newflags & VM_WRITE)) {
 442                 populate_vma_page_range(vma, start, end, NULL);
 443         }
 444
 445         vm_stat_account(mm, oldflags, -nrpages);
 446         vm_stat_account(mm, newflags, nrpages);
 447         perf_event_mmap(vma);
 448         return 0;
 449
 450 fail:
 451         vm_unacct_memory(charged);
 452         return error;
 453 }
 454
 455 /*
 456  * pkey==-1 when doing a legacy mprotect()
 457  */
 458 static int do_mprotect_pkey(unsigned long start, size_t len,
 459                 unsigned long prot, int pkey)
 460 {
 461         unsigned long nstart, end, tmp, reqprot;
 462         struct vm_area_struct *vma, *prev;
 463         int error = -EINVAL;
 464         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 465         const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
 466                                 (prot & PROT_READ);
 467
 468         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 469         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 470                 return -EINVAL;
 471
 472         if (start & ~PAGE_MASK)
 473                 return -EINVAL;
 474         if (!len)
 475                 return 0;
 476         len = PAGE_ALIGN(len);
 477         end = start + len;
 478         if (end <= start)
 479                 return -ENOMEM;
 480         if (!arch_validate_prot(prot, start))
 481                 return -EINVAL;
 482
 483         reqprot = prot;
 484
 485         if (down_write_killable(&current->mm->mmap_sem))
 486                 return -EINTR;
 487
 488         /*
 489          * If userspace did not allocate the pkey, do not let
 490          * them use it here.
 491          */
 492         error = -EINVAL;
 493         if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
 494                 goto out;
 495
 496         vma = find_vma(current->mm, start);
 497         error = -ENOMEM;
 498         if (!vma)
 499                 goto out;
 500         prev = vma->vm_prev;
 501         if (unlikely(grows & PROT_GROWSDOWN)) {
 502                 if (vma->vm_start >= end)
 503                         goto out;
 504                 start = vma->vm_start;
 505                 error = -EINVAL;
 506                 if (!(vma->vm_flags & VM_GROWSDOWN))
 507                         goto out;
 508         } else {
 509                 if (vma->vm_start > start)
 510                         goto out;
 511                 if (unlikely(grows & PROT_GROWSUP)) {
 512                         end = vma->vm_end;
 513                         error = -EINVAL;
 514                         if (!(vma->vm_flags & VM_GROWSUP))
 515                                 goto out;
 516                 }
 517         }
 518         if (start > vma->vm_start)
 519                 prev = vma;
 520
 521         for (nstart = start ; ; ) {
 522                 unsigned long mask_off_old_flags;
 523                 unsigned long newflags;
 524                 int new_vma_pkey;
 525
 526                 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 527
 528                 /* Does the application expect PROT_READ to imply PROT_EXEC */
 529                 if (rier && (vma->vm_flags & VM_MAYEXEC))
 530                         prot |= PROT_EXEC;
 531
 532                 /*
 533                  * Each mprotect() call explicitly passes r/w/x permissions.
 534                  * If a permission is not passed to mprotect(), it must be
 535                  * cleared from the VMA.
 536                  */
 537                 mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
 538                                         VM_FLAGS_CLEAR;
 539
 540                 new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
 541                 newflags = calc_vm_prot_bits(prot, new_vma_pkey);
 542                 newflags |= (vma->vm_flags & ~mask_off_old_flags);
 543
 544                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 545                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 546                         error = -EACCES;
 547                         goto out;
 548                 }
 549
 550                 error = security_file_mprotect(vma, reqprot, prot);
 551                 if (error)
 552                         goto out;
 553
 554                 tmp = vma->vm_end;
 555                 if (tmp > end)
 556                         tmp = end;
 557                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 558                 if (error)
 559                         goto out;
 560                 nstart = tmp;
 561
 562                 if (nstart < prev->vm_end)
 563                         nstart = prev->vm_end;
 564                 if (nstart >= end)
 565                         goto out;
 566
 567                 vma = prev->vm_next;
 568                 if (!vma || vma->vm_start != nstart) {
 569                         error = -ENOMEM;
 570                         goto out;
 571                 }
 572                 prot = reqprot;
 573         }
 574 out:
 575         up_write(&current->mm->mmap_sem);
 576         return error;
 577 }
 578
 579 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 580                 unsigned long, prot)
 581 {
 582         return do_mprotect_pkey(start, len, prot, -1);
 583 }
 584
 585 #ifdef CONFIG_ARCH_HAS_PKEYS
 586
 587 SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
 588                 unsigned long, prot, int, pkey)
 589 {
 590         return do_mprotect_pkey(start, len, prot, pkey);
 591 }
 592
 593 SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
 594 {
 595         int pkey;
 596         int ret;
 597
 598         /* No flags supported yet. */
 599         if (flags)
 600                 return -EINVAL;
 601         /* check for unsupported init values */
 602         if (init_val & ~PKEY_ACCESS_MASK)
 603                 return -EINVAL;
 604
 605         down_write(&current->mm->mmap_sem);
 606         pkey = mm_pkey_alloc(current->mm);
 607
 608         ret = -ENOSPC;
 609         if (pkey == -1)
 610                 goto out;
 611
 612         ret = arch_set_user_pkey_access(current, pkey, init_val);
 613         if (ret) {
 614                 mm_pkey_free(current->mm, pkey);
 615                 goto out;
 616         }
 617         ret = pkey;
 618 out:
 619         up_write(&current->mm->mmap_sem);
 620         return ret;
 621 }
 622
 623 SYSCALL_DEFINE1(pkey_free, int, pkey)
 624 {
 625         int ret;
 626
 627         down_write(&current->mm->mmap_sem);
 628         ret = mm_pkey_free(current->mm, pkey);
 629         up_write(&current->mm->mmap_sem);
 630
 631         /*
 632          * We could provie warnings or errors if any VMA still
 633          * has the pkey set here.
 634          */
 635         return ret;
 636 }
 637
 638 #endif /* CONFIG_ARCH_HAS_PKEYS */