LXR linux/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/pkeys.h>
  27#include <linux/ksm.h>
  28#include <linux/uaccess.h>
  29#include <asm/pgtable.h>
  30#include <asm/cacheflush.h>
  31#include <asm/mmu_context.h>
  32#include <asm/tlbflush.h>
  33
  34#include "internal.h"
  35
  36/*
  37 * For a prot_numa update we only hold mmap_sem for read so there is a
  38 * potential race with faulting where a pmd was temporarily none. This
  39 * function checks for a transhuge pmd under the appropriate lock. It
  40 * returns a pte if it was successfully locked or NULL if it raced with
  41 * a transhuge insertion.
  42 */
  43static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
  44                        unsigned long addr, int prot_numa, spinlock_t **ptl)
  45{
  46        pte_t *pte;
  47        spinlock_t *pmdl;
  48
  49        /* !prot_numa is protected by mmap_sem held for write */
  50        if (!prot_numa)
  51                return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  52
  53        pmdl = pmd_lock(vma->vm_mm, pmd);
  54        if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
  55                spin_unlock(pmdl);
  56                return NULL;
  57        }
  58
  59        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  60        spin_unlock(pmdl);
  61        return pte;
  62}
  63
  64static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  65                unsigned long addr, unsigned long end, pgprot_t newprot,
  66                int dirty_accountable, int prot_numa)
  67{
  68        struct mm_struct *mm = vma->vm_mm;
  69        pte_t *pte, oldpte;
  70        spinlock_t *ptl;
  71        unsigned long pages = 0;
  72        int target_node = NUMA_NO_NODE;
  73
  74        pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
  75        if (!pte)
  76                return 0;
  77
  78        /* Get target node for single threaded private VMAs */
  79        if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
  80            atomic_read(&vma->vm_mm->mm_users) == 1)
  81                target_node = numa_node_id();
  82
  83        arch_enter_lazy_mmu_mode();
  84        do {
  85                oldpte = *pte;
  86                if (pte_present(oldpte)) {
  87                        pte_t ptent;
  88                        bool preserve_write = prot_numa && pte_write(oldpte);
  89
  90                        /*
  91                         * Avoid trapping faults against the zero or KSM
  92                         * pages. See similar comment in change_huge_pmd.
  93                         */
  94                        if (prot_numa) {
  95                                struct page *page;
  96
  97                                page = vm_normal_page(vma, addr, oldpte);
  98                                if (!page || PageKsm(page))
  99                                        continue;
 100
 101                                /* Avoid TLB flush if possible */
 102                                if (pte_protnone(oldpte))
 103                                        continue;
 104
 105                                /*
 106                                 * Don't mess with PTEs if page is already on the node
 107                                 * a single-threaded process is running on.
 108                                 */
 109                                if (target_node == page_to_nid(page))
 110                                        continue;
 111                        }
 112
 113                        ptent = ptep_modify_prot_start(mm, addr, pte);
 114                        ptent = pte_modify(ptent, newprot);
 115                        if (preserve_write)
 116                                ptent = pte_mkwrite(ptent);
 117
 118                        /* Avoid taking write faults for known dirty pages */
 119                        if (dirty_accountable && pte_dirty(ptent) &&
 120                                        (pte_soft_dirty(ptent) ||
 121                                         !(vma->vm_flags & VM_SOFTDIRTY))) {
 122                                ptent = pte_mkwrite(ptent);
 123                        }
 124                        ptep_modify_prot_commit(mm, addr, pte, ptent);
 125                        pages++;
 126                } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 127                        swp_entry_t entry = pte_to_swp_entry(oldpte);
 128
 129                        if (is_write_migration_entry(entry)) {
 130                                pte_t newpte;
 131                                /*
 132                                 * A protection check is difficult so
 133                                 * just be safe and disable write
 134                                 */
 135                                make_migration_entry_read(&entry);
 136                                newpte = swp_entry_to_pte(entry);
 137                                if (pte_swp_soft_dirty(oldpte))
 138                                        newpte = pte_swp_mksoft_dirty(newpte);
 139                                set_pte_at(mm, addr, pte, newpte);
 140
 141                                pages++;
 142                        }
 143                }
 144        } while (pte++, addr += PAGE_SIZE, addr != end);
 145        arch_leave_lazy_mmu_mode();
 146        pte_unmap_unlock(pte - 1, ptl);
 147
 148        return pages;
 149}
 150
 151static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 152                pud_t *pud, unsigned long addr, unsigned long end,
 153                pgprot_t newprot, int dirty_accountable, int prot_numa)
 154{
 155        pmd_t *pmd;
 156        struct mm_struct *mm = vma->vm_mm;
 157        unsigned long next;
 158        unsigned long pages = 0;
 159        unsigned long nr_huge_updates = 0;
 160        unsigned long mni_start = 0;
 161
 162        pmd = pmd_offset(pud, addr);
 163        do {
 164                unsigned long this_pages;
 165
 166                next = pmd_addr_end(addr, end);
 167                if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
 168                                && pmd_none_or_clear_bad(pmd))
 169                        continue;
 170
 171                /* invoke the mmu notifier if the pmd is populated */
 172                if (!mni_start) {
 173                        mni_start = addr;
 174                        mmu_notifier_invalidate_range_start(mm, mni_start, end);
 175                }
 176
 177                if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
 178                        if (next - addr != HPAGE_PMD_SIZE) {
 179                                __split_huge_pmd(vma, pmd, addr, false, NULL);
 180                                if (pmd_trans_unstable(pmd))
 181                                        continue;
 182                        } else {
 183                                int nr_ptes = change_huge_pmd(vma, pmd, addr,
 184                                                newprot, prot_numa);
 185
 186                                if (nr_ptes) {
 187                                        if (nr_ptes == HPAGE_PMD_NR) {
 188                                                pages += HPAGE_PMD_NR;
 189                                                nr_huge_updates++;
 190                                        }
 191
 192                                        /* huge pmd was handled */
 193                                        continue;
 194                                }
 195                        }
 196                        /* fall through, the trans huge pmd just split */
 197                }
 198                this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 199                                 dirty_accountable, prot_numa);
 200                pages += this_pages;
 201        } while (pmd++, addr = next, addr != end);
 202
 203        if (mni_start)
 204                mmu_notifier_invalidate_range_end(mm, mni_start, end);
 205
 206        if (nr_huge_updates)
 207                count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 208        return pages;
 209}
 210
 211static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 212                pgd_t *pgd, unsigned long addr, unsigned long end,
 213                pgprot_t newprot, int dirty_accountable, int prot_numa)
 214{
 215        pud_t *pud;
 216        unsigned long next;
 217        unsigned long pages = 0;
 218
 219        pud = pud_offset(pgd, addr);
 220        do {
 221                next = pud_addr_end(addr, end);
 222                if (pud_none_or_clear_bad(pud))
 223                        continue;
 224                pages += change_pmd_range(vma, pud, addr, next, newprot,
 225                                 dirty_accountable, prot_numa);
 226        } while (pud++, addr = next, addr != end);
 227
 228        return pages;
 229}
 230
 231static unsigned long change_protection_range(struct vm_area_struct *vma,
 232                unsigned long addr, unsigned long end, pgprot_t newprot,
 233                int dirty_accountable, int prot_numa)
 234{
 235        struct mm_struct *mm = vma->vm_mm;
 236        pgd_t *pgd;
 237        unsigned long next;
 238        unsigned long start = addr;
 239        unsigned long pages = 0;
 240
 241        BUG_ON(addr >= end);
 242        pgd = pgd_offset(mm, addr);
 243        flush_cache_range(vma, addr, end);
 244        set_tlb_flush_pending(mm);
 245        do {
 246                next = pgd_addr_end(addr, end);
 247                if (pgd_none_or_clear_bad(pgd))
 248                        continue;
 249                pages += change_pud_range(vma, pgd, addr, next, newprot,
 250                                 dirty_accountable, prot_numa);
 251        } while (pgd++, addr = next, addr != end);
 252
 253        /* Only flush the TLB if we actually modified any entries: */
 254        if (pages)
 255                flush_tlb_range(vma, start, end);
 256        clear_tlb_flush_pending(mm);
 257
 258        return pages;
 259}
 260
 261unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 262                       unsigned long end, pgprot_t newprot,
 263                       int dirty_accountable, int prot_numa)
 264{
 265        unsigned long pages;
 266
 267        if (is_vm_hugetlb_page(vma))
 268                pages = hugetlb_change_protection(vma, start, end, newprot);
 269        else
 270                pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 271
 272        return pages;
 273}
 274
 275int
 276mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 277        unsigned long start, unsigned long end, unsigned long newflags)
 278{
 279        struct mm_struct *mm = vma->vm_mm;
 280        unsigned long oldflags = vma->vm_flags;
 281        long nrpages = (end - start) >> PAGE_SHIFT;
 282        unsigned long charged = 0;
 283        pgoff_t pgoff;
 284        int error;
 285        int dirty_accountable = 0;
 286
 287        if (newflags == oldflags) {
 288                *pprev = vma;
 289                return 0;
 290        }
 291
 292        /*
 293         * If we make a private mapping writable we increase our commit;
 294         * but (without finer accounting) cannot reduce our commit if we
 295         * make it unwritable again. hugetlb mapping were accounted for
 296         * even if read-only so there is no need to account for them here
 297         */
 298        if (newflags & VM_WRITE) {
 299                /* Check space limits when area turns into data. */
 300                if (!may_expand_vm(mm, newflags, nrpages) &&
 301                                may_expand_vm(mm, oldflags, nrpages))
 302                        return -ENOMEM;
 303                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 304                                                VM_SHARED|VM_NORESERVE))) {
 305                        charged = nrpages;
 306                        if (security_vm_enough_memory_mm(mm, charged))
 307                                return -ENOMEM;
 308                        newflags |= VM_ACCOUNT;
 309                }
 310        }
 311
 312        /*
 313         * First try to merge with previous and/or next vma.
 314         */
 315        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 316        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 317                           vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 318                           vma->vm_userfaultfd_ctx);
 319        if (*pprev) {
 320                vma = *pprev;
 321                VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
 322                goto success;
 323        }
 324
 325        *pprev = vma;
 326
 327        if (start != vma->vm_start) {
 328                error = split_vma(mm, vma, start, 1);
 329                if (error)
 330                        goto fail;
 331        }
 332
 333        if (end != vma->vm_end) {
 334                error = split_vma(mm, vma, end, 0);
 335                if (error)
 336                        goto fail;
 337        }
 338
 339success:
 340        /*
 341         * vm_flags and vm_page_prot are protected by the mmap_sem
 342         * held in write mode.
 343         */
 344        vma->vm_flags = newflags;
 345        dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
 346        vma_set_page_prot(vma);
 347
 348        change_protection(vma, start, end, vma->vm_page_prot,
 349                          dirty_accountable, 0);
 350
 351        /*
 352         * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 353         * fault on access.
 354         */
 355        if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 356                        (newflags & VM_WRITE)) {
 357                populate_vma_page_range(vma, start, end, NULL);
 358        }
 359
 360        vm_stat_account(mm, oldflags, -nrpages);
 361        vm_stat_account(mm, newflags, nrpages);
 362        perf_event_mmap(vma);
 363        return 0;
 364
 365fail:
 366        vm_unacct_memory(charged);
 367        return error;
 368}
 369
 370/*
 371 * pkey==-1 when doing a legacy mprotect()
 372 */
 373static int do_mprotect_pkey(unsigned long start, size_t len,
 374                unsigned long prot, int pkey)
 375{
 376        unsigned long nstart, end, tmp, reqprot;
 377        struct vm_area_struct *vma, *prev;
 378        int error = -EINVAL;
 379        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 380        const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
 381                                (prot & PROT_READ);
 382
 383        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 384        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 385                return -EINVAL;
 386
 387        if (start & ~PAGE_MASK)
 388                return -EINVAL;
 389        if (!len)
 390                return 0;
 391        len = PAGE_ALIGN(len);
 392        end = start + len;
 393        if (end <= start)
 394                return -ENOMEM;
 395        if (!arch_validate_prot(prot))
 396                return -EINVAL;
 397
 398        reqprot = prot;
 399
 400        if (down_write_killable(&current->mm->mmap_sem))
 401                return -EINTR;
 402
 403        /*
 404         * If userspace did not allocate the pkey, do not let
 405         * them use it here.
 406         */
 407        error = -EINVAL;
 408        if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
 409                goto out;
 410
 411        vma = find_vma(current->mm, start);
 412        error = -ENOMEM;
 413        if (!vma)
 414                goto out;
 415        prev = vma->vm_prev;
 416        if (unlikely(grows & PROT_GROWSDOWN)) {
 417                if (vma->vm_start >= end)
 418                        goto out;
 419                start = vma->vm_start;
 420                error = -EINVAL;
 421                if (!(vma->vm_flags & VM_GROWSDOWN))
 422                        goto out;
 423        } else {
 424                if (vma->vm_start > start)
 425                        goto out;
 426                if (unlikely(grows & PROT_GROWSUP)) {
 427                        end = vma->vm_end;
 428                        error = -EINVAL;
 429                        if (!(vma->vm_flags & VM_GROWSUP))
 430                                goto out;
 431                }
 432        }
 433        if (start > vma->vm_start)
 434                prev = vma;
 435
 436        for (nstart = start ; ; ) {
 437                unsigned long mask_off_old_flags;
 438                unsigned long newflags;
 439                int new_vma_pkey;
 440
 441                /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 442
 443                /* Does the application expect PROT_READ to imply PROT_EXEC */
 444                if (rier && (vma->vm_flags & VM_MAYEXEC))
 445                        prot |= PROT_EXEC;
 446
 447                /*
 448                 * Each mprotect() call explicitly passes r/w/x permissions.
 449                 * If a permission is not passed to mprotect(), it must be
 450                 * cleared from the VMA.
 451                 */
 452                mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
 453                                        ARCH_VM_PKEY_FLAGS;
 454
 455                new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
 456                newflags = calc_vm_prot_bits(prot, new_vma_pkey);
 457                newflags |= (vma->vm_flags & ~mask_off_old_flags);
 458
 459                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 460                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 461                        error = -EACCES;
 462                        goto out;
 463                }
 464
 465                error = security_file_mprotect(vma, reqprot, prot);
 466                if (error)
 467                        goto out;
 468
 469                tmp = vma->vm_end;
 470                if (tmp > end)
 471                        tmp = end;
 472                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 473                if (error)
 474                        goto out;
 475                nstart = tmp;
 476
 477                if (nstart < prev->vm_end)
 478                        nstart = prev->vm_end;
 479                if (nstart >= end)
 480                        goto out;
 481
 482                vma = prev->vm_next;
 483                if (!vma || vma->vm_start != nstart) {
 484                        error = -ENOMEM;
 485                        goto out;
 486                }
 487                prot = reqprot;
 488        }
 489out:
 490        up_write(&current->mm->mmap_sem);
 491        return error;
 492}
 493
 494SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 495                unsigned long, prot)
 496{
 497        return do_mprotect_pkey(start, len, prot, -1);
 498}
 499
 500#ifdef CONFIG_ARCH_HAS_PKEYS
 501
 502SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
 503                unsigned long, prot, int, pkey)
 504{
 505        return do_mprotect_pkey(start, len, prot, pkey);
 506}
 507
 508SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
 509{
 510        int pkey;
 511        int ret;
 512
 513        /* No flags supported yet. */
 514        if (flags)
 515                return -EINVAL;
 516        /* check for unsupported init values */
 517        if (init_val & ~PKEY_ACCESS_MASK)
 518                return -EINVAL;
 519
 520        down_write(&current->mm->mmap_sem);
 521        pkey = mm_pkey_alloc(current->mm);
 522
 523        ret = -ENOSPC;
 524        if (pkey == -1)
 525                goto out;
 526
 527        ret = arch_set_user_pkey_access(current, pkey, init_val);
 528        if (ret) {
 529                mm_pkey_free(current->mm, pkey);
 530                goto out;
 531        }
 532        ret = pkey;
 533out:
 534        up_write(&current->mm->mmap_sem);
 535        return ret;
 536}
 537
 538SYSCALL_DEFINE1(pkey_free, int, pkey)
 539{
 540        int ret;
 541
 542        down_write(&current->mm->mmap_sem);
 543        ret = mm_pkey_free(current->mm, pkey);
 544        up_write(&current->mm->mmap_sem);
 545
 546        /*
 547         * We could provie warnings or errors if any VMA still
 548         * has the pkey set here.
 549         */
 550        return ret;
 551}
 552
 553#endif /* CONFIG_ARCH_HAS_PKEYS */
 554