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/*
  33 * For a prot_numa update we only hold mmap_sem for read so there is a
  34 * potential race with faulting where a pmd was temporarily none. This
  35 * function checks for a transhuge pmd under the appropriate lock. It
  36 * returns a pte if it was successfully locked or NULL if it raced with
  37 * a transhuge insertion.
  38 */
  39static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
  40                        unsigned long addr, int prot_numa, spinlock_t **ptl)
  41{
  42        pte_t *pte;
  43        spinlock_t *pmdl;
  44
  45        /* !prot_numa is protected by mmap_sem held for write */
  46        if (!prot_numa)
  47                return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  48
  49        pmdl = pmd_lock(vma->vm_mm, pmd);
  50        if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
  51                spin_unlock(pmdl);
  52                return NULL;
  53        }
  54
  55        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  56        spin_unlock(pmdl);
  57        return pte;
  58}
  59
  60static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  61                unsigned long addr, unsigned long end, pgprot_t newprot,
  62                int dirty_accountable, int prot_numa)
  63{
  64        struct mm_struct *mm = vma->vm_mm;
  65        pte_t *pte, oldpte;
  66        spinlock_t *ptl;
  67        unsigned long pages = 0;
  68
  69        pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
  70        if (!pte)
  71                return 0;
  72
  73        arch_enter_lazy_mmu_mode();
  74        do {
  75                oldpte = *pte;
  76                if (pte_present(oldpte)) {
  77                        pte_t ptent;
  78                        bool preserve_write = prot_numa && pte_write(oldpte);
  79
  80                        /*
  81                         * Avoid trapping faults against the zero or KSM
  82                         * pages. See similar comment in change_huge_pmd.
  83                         */
  84                        if (prot_numa) {
  85                                struct page *page;
  86
  87                                page = vm_normal_page(vma, addr, oldpte);
  88                                if (!page || PageKsm(page))
  89                                        continue;
  90
  91                                /* Avoid TLB flush if possible */
  92                                if (pte_protnone(oldpte))
  93                                        continue;
  94                        }
  95
  96                        ptent = ptep_modify_prot_start(mm, addr, pte);
  97                        ptent = pte_modify(ptent, newprot);
  98                        if (preserve_write)
  99                                ptent = pte_mkwrite(ptent);
 100
 101                        /* Avoid taking write faults for known dirty pages */
 102                        if (dirty_accountable && pte_dirty(ptent) &&
 103                                        (pte_soft_dirty(ptent) ||
 104                                         !(vma->vm_flags & VM_SOFTDIRTY))) {
 105                                ptent = pte_mkwrite(ptent);
 106                        }
 107                        ptep_modify_prot_commit(mm, addr, pte, ptent);
 108                        pages++;
 109                } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 110                        swp_entry_t entry = pte_to_swp_entry(oldpte);
 111
 112                        if (is_write_migration_entry(entry)) {
 113                                pte_t newpte;
 114                                /*
 115                                 * A protection check is difficult so
 116                                 * just be safe and disable write
 117                                 */
 118                                make_migration_entry_read(&entry);
 119                                newpte = swp_entry_to_pte(entry);
 120                                if (pte_swp_soft_dirty(oldpte))
 121                                        newpte = pte_swp_mksoft_dirty(newpte);
 122                                set_pte_at(mm, addr, pte, newpte);
 123
 124                                pages++;
 125                        }
 126                }
 127        } while (pte++, addr += PAGE_SIZE, addr != end);
 128        arch_leave_lazy_mmu_mode();
 129        pte_unmap_unlock(pte - 1, ptl);
 130
 131        return pages;
 132}
 133
 134static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 135                pud_t *pud, unsigned long addr, unsigned long end,
 136                pgprot_t newprot, int dirty_accountable, int prot_numa)
 137{
 138        pmd_t *pmd;
 139        struct mm_struct *mm = vma->vm_mm;
 140        unsigned long next;
 141        unsigned long pages = 0;
 142        unsigned long nr_huge_updates = 0;
 143        unsigned long mni_start = 0;
 144
 145        pmd = pmd_offset(pud, addr);
 146        do {
 147                unsigned long this_pages;
 148
 149                next = pmd_addr_end(addr, end);
 150                if (!pmd_trans_huge(*pmd) && pmd_none_or_clear_bad(pmd))
 151                        continue;
 152
 153                /* invoke the mmu notifier if the pmd is populated */
 154                if (!mni_start) {
 155                        mni_start = addr;
 156                        mmu_notifier_invalidate_range_start(mm, mni_start, end);
 157                }
 158
 159                if (pmd_trans_huge(*pmd)) {
 160                        if (next - addr != HPAGE_PMD_SIZE)
 161                                split_huge_page_pmd(vma, addr, pmd);
 162                        else {
 163                                int nr_ptes = change_huge_pmd(vma, pmd, addr,
 164                                                newprot, prot_numa);
 165
 166                                if (nr_ptes) {
 167                                        if (nr_ptes == HPAGE_PMD_NR) {
 168                                                pages += HPAGE_PMD_NR;
 169                                                nr_huge_updates++;
 170                                        }
 171
 172                                        /* huge pmd was handled */
 173                                        continue;
 174                                }
 175                        }
 176                        /* fall through, the trans huge pmd just split */
 177                }
 178                this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 179                                 dirty_accountable, prot_numa);
 180                pages += this_pages;
 181        } while (pmd++, addr = next, addr != end);
 182
 183        if (mni_start)
 184                mmu_notifier_invalidate_range_end(mm, mni_start, end);
 185
 186        if (nr_huge_updates)
 187                count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 188        return pages;
 189}
 190
 191static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 192                pgd_t *pgd, unsigned long addr, unsigned long end,
 193                pgprot_t newprot, int dirty_accountable, int prot_numa)
 194{
 195        pud_t *pud;
 196        unsigned long next;
 197        unsigned long pages = 0;
 198
 199        pud = pud_offset(pgd, addr);
 200        do {
 201                next = pud_addr_end(addr, end);
 202                if (pud_none_or_clear_bad(pud))
 203                        continue;
 204                pages += change_pmd_range(vma, pud, addr, next, newprot,
 205                                 dirty_accountable, prot_numa);
 206        } while (pud++, addr = next, addr != end);
 207
 208        return pages;
 209}
 210
 211static unsigned long change_protection_range(struct vm_area_struct *vma,
 212                unsigned long addr, unsigned long end, pgprot_t newprot,
 213                int dirty_accountable, int prot_numa)
 214{
 215        struct mm_struct *mm = vma->vm_mm;
 216        pgd_t *pgd;
 217        unsigned long next;
 218        unsigned long start = addr;
 219        unsigned long pages = 0;
 220
 221        BUG_ON(addr >= end);
 222        pgd = pgd_offset(mm, addr);
 223        flush_cache_range(vma, addr, end);
 224        set_tlb_flush_pending(mm);
 225        do {
 226                next = pgd_addr_end(addr, end);
 227                if (pgd_none_or_clear_bad(pgd))
 228                        continue;
 229                pages += change_pud_range(vma, pgd, addr, next, newprot,
 230                                 dirty_accountable, prot_numa);
 231        } while (pgd++, addr = next, addr != end);
 232
 233        /* Only flush the TLB if we actually modified any entries: */
 234        if (pages)
 235                flush_tlb_range(vma, start, end);
 236        clear_tlb_flush_pending(mm);
 237
 238        return pages;
 239}
 240
 241unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 242                       unsigned long end, pgprot_t newprot,
 243                       int dirty_accountable, int prot_numa)
 244{
 245        unsigned long pages;
 246
 247        if (is_vm_hugetlb_page(vma))
 248                pages = hugetlb_change_protection(vma, start, end, newprot);
 249        else
 250                pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 251
 252        return pages;
 253}
 254
 255int
 256mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 257        unsigned long start, unsigned long end, unsigned long newflags)
 258{
 259        struct mm_struct *mm = vma->vm_mm;
 260        unsigned long oldflags = vma->vm_flags;
 261        long nrpages = (end - start) >> PAGE_SHIFT;
 262        unsigned long charged = 0;
 263        pgoff_t pgoff;
 264        int error;
 265        int dirty_accountable = 0;
 266
 267        if (newflags == oldflags) {
 268                *pprev = vma;
 269                return 0;
 270        }
 271
 272        /*
 273         * If we make a private mapping writable we increase our commit;
 274         * but (without finer accounting) cannot reduce our commit if we
 275         * make it unwritable again. hugetlb mapping were accounted for
 276         * even if read-only so there is no need to account for them here
 277         */
 278        if (newflags & VM_WRITE) {
 279                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 280                                                VM_SHARED|VM_NORESERVE))) {
 281                        charged = nrpages;
 282                        if (security_vm_enough_memory_mm(mm, charged))
 283                                return -ENOMEM;
 284                        newflags |= VM_ACCOUNT;
 285                }
 286        }
 287
 288        /*
 289         * First try to merge with previous and/or next vma.
 290         */
 291        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 292        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 293                        vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 294        if (*pprev) {
 295                vma = *pprev;
 296                goto success;
 297        }
 298
 299        *pprev = vma;
 300
 301        if (start != vma->vm_start) {
 302                error = split_vma(mm, vma, start, 1);
 303                if (error)
 304                        goto fail;
 305        }
 306
 307        if (end != vma->vm_end) {
 308                error = split_vma(mm, vma, end, 0);
 309                if (error)
 310                        goto fail;
 311        }
 312
 313success:
 314        /*
 315         * vm_flags and vm_page_prot are protected by the mmap_sem
 316         * held in write mode.
 317         */
 318        vma->vm_flags = newflags;
 319        dirty_accountable = vma_wants_writenotify(vma);
 320        vma_set_page_prot(vma);
 321
 322        change_protection(vma, start, end, vma->vm_page_prot,
 323                          dirty_accountable, 0);
 324
 325        vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 326        vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 327        perf_event_mmap(vma);
 328        return 0;
 329
 330fail:
 331        vm_unacct_memory(charged);
 332        return error;
 333}
 334
 335SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 336                unsigned long, prot)
 337{
 338        unsigned long vm_flags, nstart, end, tmp, reqprot;
 339        struct vm_area_struct *vma, *prev;
 340        int error = -EINVAL;
 341        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 342        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 343        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 344                return -EINVAL;
 345
 346        if (start & ~PAGE_MASK)
 347                return -EINVAL;
 348        if (!len)
 349                return 0;
 350        len = PAGE_ALIGN(len);
 351        end = start + len;
 352        if (end <= start)
 353                return -ENOMEM;
 354        if (!arch_validate_prot(prot))
 355                return -EINVAL;
 356
 357        reqprot = prot;
 358        /*
 359         * Does the application expect PROT_READ to imply PROT_EXEC:
 360         */
 361        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 362                prot |= PROT_EXEC;
 363
 364        vm_flags = calc_vm_prot_bits(prot);
 365
 366        down_write(&current->mm->mmap_sem);
 367
 368        vma = find_vma(current->mm, start);
 369        error = -ENOMEM;
 370        if (!vma)
 371                goto out;
 372        prev = vma->vm_prev;
 373        if (unlikely(grows & PROT_GROWSDOWN)) {
 374                if (vma->vm_start >= end)
 375                        goto out;
 376                start = vma->vm_start;
 377                error = -EINVAL;
 378                if (!(vma->vm_flags & VM_GROWSDOWN))
 379                        goto out;
 380        } else {
 381                if (vma->vm_start > start)
 382                        goto out;
 383                if (unlikely(grows & PROT_GROWSUP)) {
 384                        end = vma->vm_end;
 385                        error = -EINVAL;
 386                        if (!(vma->vm_flags & VM_GROWSUP))
 387                                goto out;
 388                }
 389        }
 390        if (start > vma->vm_start)
 391                prev = vma;
 392
 393        for (nstart = start ; ; ) {
 394                unsigned long newflags;
 395
 396                /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 397
 398                newflags = vm_flags;
 399                newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 400
 401                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 402                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 403                        error = -EACCES;
 404                        goto out;
 405                }
 406
 407                error = security_file_mprotect(vma, reqprot, prot);
 408                if (error)
 409                        goto out;
 410
 411                tmp = vma->vm_end;
 412                if (tmp > end)
 413                        tmp = end;
 414                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 415                if (error)
 416                        goto out;
 417                nstart = tmp;
 418
 419                if (nstart < prev->vm_end)
 420                        nstart = prev->vm_end;
 421                if (nstart >= end)
 422                        goto out;
 423
 424                vma = prev->vm_next;
 425                if (!vma || vma->vm_start != nstart) {
 426                        error = -ENOMEM;
 427                        goto out;
 428                }
 429        }
 430out:
 431        up_write(&current->mm->mmap_sem);
 432        return error;
 433}
 434