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/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 */
  41static 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
  62static 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        arch_enter_lazy_mmu_mode();
  76        do {
  77                oldpte = *pte;
  78                if (pte_present(oldpte)) {
  79                        pte_t ptent;
  80                        bool preserve_write = prot_numa && pte_write(oldpte);
  81
  82                        /*
  83                         * Avoid trapping faults against the zero or KSM
  84                         * pages. See similar comment in change_huge_pmd.
  85                         */
  86                        if (prot_numa) {
  87                                struct page *page;
  88
  89                                page = vm_normal_page(vma, addr, oldpte);
  90                                if (!page || PageKsm(page))
  91                                        continue;
  92
  93                                /* Avoid TLB flush if possible */
  94                                if (pte_protnone(oldpte))
  95                                        continue;
  96                        }
  97
  98                        ptent = ptep_modify_prot_start(mm, addr, pte);
  99                        ptent = pte_modify(ptent, newprot);
 100                        if (preserve_write)
 101                                ptent = pte_mkwrite(ptent);
 102
 103                        /* Avoid taking write faults for known dirty pages */
 104                        if (dirty_accountable && pte_dirty(ptent) &&
 105                                        (pte_soft_dirty(ptent) ||
 106                                         !(vma->vm_flags & VM_SOFTDIRTY))) {
 107                                ptent = pte_mkwrite(ptent);
 108                        }
 109                        ptep_modify_prot_commit(mm, addr, pte, ptent);
 110                        pages++;
 111                } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 112                        swp_entry_t entry = pte_to_swp_entry(oldpte);
 113
 114                        if (is_write_migration_entry(entry)) {
 115                                pte_t newpte;
 116                                /*
 117                                 * A protection check is difficult so
 118                                 * just be safe and disable write
 119                                 */
 120                                make_migration_entry_read(&entry);
 121                                newpte = swp_entry_to_pte(entry);
 122                                if (pte_swp_soft_dirty(oldpte))
 123                                        newpte = pte_swp_mksoft_dirty(newpte);
 124                                set_pte_at(mm, addr, pte, newpte);
 125
 126                                pages++;
 127                        }
 128                }
 129        } while (pte++, addr += PAGE_SIZE, addr != end);
 130        arch_leave_lazy_mmu_mode();
 131        pte_unmap_unlock(pte - 1, ptl);
 132
 133        return pages;
 134}
 135
 136static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 137                pud_t *pud, unsigned long addr, unsigned long end,
 138                pgprot_t newprot, int dirty_accountable, int prot_numa)
 139{
 140        pmd_t *pmd;
 141        struct mm_struct *mm = vma->vm_mm;
 142        unsigned long next;
 143        unsigned long pages = 0;
 144        unsigned long nr_huge_updates = 0;
 145        unsigned long mni_start = 0;
 146
 147        pmd = pmd_offset(pud, addr);
 148        do {
 149                unsigned long this_pages;
 150
 151                next = pmd_addr_end(addr, end);
 152                if (!pmd_trans_huge(*pmd) && pmd_none_or_clear_bad(pmd))
 153                        continue;
 154
 155                /* invoke the mmu notifier if the pmd is populated */
 156                if (!mni_start) {
 157                        mni_start = addr;
 158                        mmu_notifier_invalidate_range_start(mm, mni_start, end);
 159                }
 160
 161                if (pmd_trans_huge(*pmd)) {
 162                        if (next - addr != HPAGE_PMD_SIZE)
 163                                split_huge_page_pmd(vma, addr, pmd);
 164                        else {
 165                                int nr_ptes = change_huge_pmd(vma, pmd, addr,
 166                                                newprot, prot_numa);
 167
 168                                if (nr_ptes) {
 169                                        if (nr_ptes == HPAGE_PMD_NR) {
 170                                                pages += HPAGE_PMD_NR;
 171                                                nr_huge_updates++;
 172                                        }
 173
 174                                        /* huge pmd was handled */
 175                                        continue;
 176                                }
 177                        }
 178                        /* fall through, the trans huge pmd just split */
 179                }
 180                this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 181                                 dirty_accountable, prot_numa);
 182                pages += this_pages;
 183        } while (pmd++, addr = next, addr != end);
 184
 185        if (mni_start)
 186                mmu_notifier_invalidate_range_end(mm, mni_start, end);
 187
 188        if (nr_huge_updates)
 189                count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 190        return pages;
 191}
 192
 193static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 194                pgd_t *pgd, unsigned long addr, unsigned long end,
 195                pgprot_t newprot, int dirty_accountable, int prot_numa)
 196{
 197        pud_t *pud;
 198        unsigned long next;
 199        unsigned long pages = 0;
 200
 201        pud = pud_offset(pgd, addr);
 202        do {
 203                next = pud_addr_end(addr, end);
 204                if (pud_none_or_clear_bad(pud))
 205                        continue;
 206                pages += change_pmd_range(vma, pud, addr, next, newprot,
 207                                 dirty_accountable, prot_numa);
 208        } while (pud++, addr = next, addr != end);
 209
 210        return pages;
 211}
 212
 213static unsigned long change_protection_range(struct vm_area_struct *vma,
 214                unsigned long addr, unsigned long end, pgprot_t newprot,
 215                int dirty_accountable, int prot_numa)
 216{
 217        struct mm_struct *mm = vma->vm_mm;
 218        pgd_t *pgd;
 219        unsigned long next;
 220        unsigned long start = addr;
 221        unsigned long pages = 0;
 222
 223        BUG_ON(addr >= end);
 224        pgd = pgd_offset(mm, addr);
 225        flush_cache_range(vma, addr, end);
 226        set_tlb_flush_pending(mm);
 227        do {
 228                next = pgd_addr_end(addr, end);
 229                if (pgd_none_or_clear_bad(pgd))
 230                        continue;
 231                pages += change_pud_range(vma, pgd, addr, next, newprot,
 232                                 dirty_accountable, prot_numa);
 233        } while (pgd++, addr = next, addr != end);
 234
 235        /* Only flush the TLB if we actually modified any entries: */
 236        if (pages)
 237                flush_tlb_range(vma, start, end);
 238        clear_tlb_flush_pending(mm);
 239
 240        return pages;
 241}
 242
 243unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 244                       unsigned long end, pgprot_t newprot,
 245                       int dirty_accountable, int prot_numa)
 246{
 247        unsigned long pages;
 248
 249        if (is_vm_hugetlb_page(vma))
 250                pages = hugetlb_change_protection(vma, start, end, newprot);
 251        else
 252                pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 253
 254        return pages;
 255}
 256
 257int
 258mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 259        unsigned long start, unsigned long end, unsigned long newflags)
 260{
 261        struct mm_struct *mm = vma->vm_mm;
 262        unsigned long oldflags = vma->vm_flags;
 263        long nrpages = (end - start) >> PAGE_SHIFT;
 264        unsigned long charged = 0;
 265        pgoff_t pgoff;
 266        int error;
 267        int dirty_accountable = 0;
 268
 269        if (newflags == oldflags) {
 270                *pprev = vma;
 271                return 0;
 272        }
 273
 274        /*
 275         * If we make a private mapping writable we increase our commit;
 276         * but (without finer accounting) cannot reduce our commit if we
 277         * make it unwritable again. hugetlb mapping were accounted for
 278         * even if read-only so there is no need to account for them here
 279         */
 280        if (newflags & VM_WRITE) {
 281                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 282                                                VM_SHARED|VM_NORESERVE))) {
 283                        charged = nrpages;
 284                        if (security_vm_enough_memory_mm(mm, charged))
 285                                return -ENOMEM;
 286                        newflags |= VM_ACCOUNT;
 287                }
 288        }
 289
 290        /*
 291         * First try to merge with previous and/or next vma.
 292         */
 293        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 294        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 295                           vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 296                           vma->vm_userfaultfd_ctx);
 297        if (*pprev) {
 298                vma = *pprev;
 299                goto success;
 300        }
 301
 302        *pprev = vma;
 303
 304        if (start != vma->vm_start) {
 305                error = split_vma(mm, vma, start, 1);
 306                if (error)
 307                        goto fail;
 308        }
 309
 310        if (end != vma->vm_end) {
 311                error = split_vma(mm, vma, end, 0);
 312                if (error)
 313                        goto fail;
 314        }
 315
 316success:
 317        /*
 318         * vm_flags and vm_page_prot are protected by the mmap_sem
 319         * held in write mode.
 320         */
 321        vma->vm_flags = newflags;
 322        dirty_accountable = vma_wants_writenotify(vma);
 323        vma_set_page_prot(vma);
 324
 325        change_protection(vma, start, end, vma->vm_page_prot,
 326                          dirty_accountable, 0);
 327
 328        /*
 329         * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 330         * fault on access.
 331         */
 332        if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 333                        (newflags & VM_WRITE)) {
 334                populate_vma_page_range(vma, start, end, NULL);
 335        }
 336
 337        vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 338        vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 339        perf_event_mmap(vma);
 340        return 0;
 341
 342fail:
 343        vm_unacct_memory(charged);
 344        return error;
 345}
 346
 347SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 348                unsigned long, prot)
 349{
 350        unsigned long vm_flags, nstart, end, tmp, reqprot;
 351        struct vm_area_struct *vma, *prev;
 352        int error = -EINVAL;
 353        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 354        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 355        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 356                return -EINVAL;
 357
 358        if (start & ~PAGE_MASK)
 359                return -EINVAL;
 360        if (!len)
 361                return 0;
 362        len = PAGE_ALIGN(len);
 363        end = start + len;
 364        if (end <= start)
 365                return -ENOMEM;
 366        if (!arch_validate_prot(prot))
 367                return -EINVAL;
 368
 369        reqprot = prot;
 370        /*
 371         * Does the application expect PROT_READ to imply PROT_EXEC:
 372         */
 373        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 374                prot |= PROT_EXEC;
 375
 376        vm_flags = calc_vm_prot_bits(prot);
 377
 378        down_write(&current->mm->mmap_sem);
 379
 380        vma = find_vma(current->mm, start);
 381        error = -ENOMEM;
 382        if (!vma)
 383                goto out;
 384        prev = vma->vm_prev;
 385        if (unlikely(grows & PROT_GROWSDOWN)) {
 386                if (vma->vm_start >= end)
 387                        goto out;
 388                start = vma->vm_start;
 389                error = -EINVAL;
 390                if (!(vma->vm_flags & VM_GROWSDOWN))
 391                        goto out;
 392        } else {
 393                if (vma->vm_start > start)
 394                        goto out;
 395                if (unlikely(grows & PROT_GROWSUP)) {
 396                        end = vma->vm_end;
 397                        error = -EINVAL;
 398                        if (!(vma->vm_flags & VM_GROWSUP))
 399                                goto out;
 400                }
 401        }
 402        if (start > vma->vm_start)
 403                prev = vma;
 404
 405        for (nstart = start ; ; ) {
 406                unsigned long newflags;
 407
 408                /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 409
 410                newflags = vm_flags;
 411                newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 412
 413                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 414                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 415                        error = -EACCES;
 416                        goto out;
 417                }
 418
 419                error = security_file_mprotect(vma, reqprot, prot);
 420                if (error)
 421                        goto out;
 422
 423                tmp = vma->vm_end;
 424                if (tmp > end)
 425                        tmp = end;
 426                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 427                if (error)
 428                        goto out;
 429                nstart = tmp;
 430
 431                if (nstart < prev->vm_end)
 432                        nstart = prev->vm_end;
 433                if (nstart >= end)
 434                        goto out;
 435
 436                vma = prev->vm_next;
 437                if (!vma || vma->vm_start != nstart) {
 438                        error = -ENOMEM;
 439                        goto out;
 440                }
 441        }
 442out:
 443        up_write(&current->mm->mmap_sem);
 444        return error;
 445}
 446