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 <asm/uaccess.h>
  27#include <asm/pgtable.h>
  28#include <asm/cacheflush.h>
  29#include <asm/tlbflush.h>
  30
  31#ifndef pgprot_modify
  32static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
  33{
  34        return newprot;
  35}
  36#endif
  37
  38static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  39                unsigned long addr, unsigned long end, pgprot_t newprot,
  40                int dirty_accountable)
  41{
  42        pte_t *pte, oldpte;
  43        spinlock_t *ptl;
  44
  45        pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  46        arch_enter_lazy_mmu_mode();
  47        do {
  48                oldpte = *pte;
  49                if (pte_present(oldpte)) {
  50                        pte_t ptent;
  51
  52                        ptent = ptep_modify_prot_start(mm, addr, pte);
  53                        ptent = pte_modify(ptent, newprot);
  54
  55                        /*
  56                         * Avoid taking write faults for pages we know to be
  57                         * dirty.
  58                         */
  59                        if (dirty_accountable && pte_dirty(ptent))
  60                                ptent = pte_mkwrite(ptent);
  61
  62                        ptep_modify_prot_commit(mm, addr, pte, ptent);
  63                } else if (PAGE_MIGRATION && !pte_file(oldpte)) {
  64                        swp_entry_t entry = pte_to_swp_entry(oldpte);
  65
  66                        if (is_write_migration_entry(entry)) {
  67                                /*
  68                                 * A protection check is difficult so
  69                                 * just be safe and disable write
  70                                 */
  71                                make_migration_entry_read(&entry);
  72                                set_pte_at(mm, addr, pte,
  73                                        swp_entry_to_pte(entry));
  74                        }
  75                }
  76        } while (pte++, addr += PAGE_SIZE, addr != end);
  77        arch_leave_lazy_mmu_mode();
  78        pte_unmap_unlock(pte - 1, ptl);
  79}
  80
  81static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  82                unsigned long addr, unsigned long end, pgprot_t newprot,
  83                int dirty_accountable)
  84{
  85        pmd_t *pmd;
  86        unsigned long next;
  87
  88        pmd = pmd_offset(pud, addr);
  89        do {
  90                next = pmd_addr_end(addr, end);
  91                if (pmd_none_or_clear_bad(pmd))
  92                        continue;
  93                change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
  94        } while (pmd++, addr = next, addr != end);
  95}
  96
  97static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
  98                unsigned long addr, unsigned long end, pgprot_t newprot,
  99                int dirty_accountable)
 100{
 101        pud_t *pud;
 102        unsigned long next;
 103
 104        pud = pud_offset(pgd, addr);
 105        do {
 106                next = pud_addr_end(addr, end);
 107                if (pud_none_or_clear_bad(pud))
 108                        continue;
 109                change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
 110        } while (pud++, addr = next, addr != end);
 111}
 112
 113static void change_protection(struct vm_area_struct *vma,
 114                unsigned long addr, unsigned long end, pgprot_t newprot,
 115                int dirty_accountable)
 116{
 117        struct mm_struct *mm = vma->vm_mm;
 118        pgd_t *pgd;
 119        unsigned long next;
 120        unsigned long start = addr;
 121
 122        BUG_ON(addr >= end);
 123        pgd = pgd_offset(mm, addr);
 124        flush_cache_range(vma, addr, end);
 125        do {
 126                next = pgd_addr_end(addr, end);
 127                if (pgd_none_or_clear_bad(pgd))
 128                        continue;
 129                change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
 130        } while (pgd++, addr = next, addr != end);
 131        flush_tlb_range(vma, start, end);
 132}
 133
 134int
 135mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 136        unsigned long start, unsigned long end, unsigned long newflags)
 137{
 138        struct mm_struct *mm = vma->vm_mm;
 139        unsigned long oldflags = vma->vm_flags;
 140        long nrpages = (end - start) >> PAGE_SHIFT;
 141        unsigned long charged = 0;
 142        pgoff_t pgoff;
 143        int error;
 144        int dirty_accountable = 0;
 145
 146        if (newflags == oldflags) {
 147                *pprev = vma;
 148                return 0;
 149        }
 150
 151        /*
 152         * If we make a private mapping writable we increase our commit;
 153         * but (without finer accounting) cannot reduce our commit if we
 154         * make it unwritable again. hugetlb mapping were accounted for
 155         * even if read-only so there is no need to account for them here
 156         */
 157        if (newflags & VM_WRITE) {
 158                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 159                                                VM_SHARED|VM_NORESERVE))) {
 160                        charged = nrpages;
 161                        if (security_vm_enough_memory(charged))
 162                                return -ENOMEM;
 163                        newflags |= VM_ACCOUNT;
 164                }
 165        }
 166
 167        /*
 168         * First try to merge with previous and/or next vma.
 169         */
 170        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 171        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 172                        vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 173        if (*pprev) {
 174                vma = *pprev;
 175                goto success;
 176        }
 177
 178        *pprev = vma;
 179
 180        if (start != vma->vm_start) {
 181                error = split_vma(mm, vma, start, 1);
 182                if (error)
 183                        goto fail;
 184        }
 185
 186        if (end != vma->vm_end) {
 187                error = split_vma(mm, vma, end, 0);
 188                if (error)
 189                        goto fail;
 190        }
 191
 192success:
 193        /*
 194         * vm_flags and vm_page_prot are protected by the mmap_sem
 195         * held in write mode.
 196         */
 197        vma->vm_flags = newflags;
 198        vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 199                                          vm_get_page_prot(newflags));
 200
 201        if (vma_wants_writenotify(vma)) {
 202                vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 203                dirty_accountable = 1;
 204        }
 205
 206        mmu_notifier_invalidate_range_start(mm, start, end);
 207        if (is_vm_hugetlb_page(vma))
 208                hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 209        else
 210                change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 211        mmu_notifier_invalidate_range_end(mm, start, end);
 212        vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 213        vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 214        return 0;
 215
 216fail:
 217        vm_unacct_memory(charged);
 218        return error;
 219}
 220
 221SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 222                unsigned long, prot)
 223{
 224        unsigned long vm_flags, nstart, end, tmp, reqprot;
 225        struct vm_area_struct *vma, *prev;
 226        int error = -EINVAL;
 227        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 228        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 229        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 230                return -EINVAL;
 231
 232        if (start & ~PAGE_MASK)
 233                return -EINVAL;
 234        if (!len)
 235                return 0;
 236        len = PAGE_ALIGN(len);
 237        end = start + len;
 238        if (end <= start)
 239                return -ENOMEM;
 240        if (!arch_validate_prot(prot))
 241                return -EINVAL;
 242
 243        reqprot = prot;
 244        /*
 245         * Does the application expect PROT_READ to imply PROT_EXEC:
 246         */
 247        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 248                prot |= PROT_EXEC;
 249
 250        vm_flags = calc_vm_prot_bits(prot);
 251
 252        down_write(&current->mm->mmap_sem);
 253
 254        vma = find_vma_prev(current->mm, start, &prev);
 255        error = -ENOMEM;
 256        if (!vma)
 257                goto out;
 258        if (unlikely(grows & PROT_GROWSDOWN)) {
 259                if (vma->vm_start >= end)
 260                        goto out;
 261                start = vma->vm_start;
 262                error = -EINVAL;
 263                if (!(vma->vm_flags & VM_GROWSDOWN))
 264                        goto out;
 265        }
 266        else {
 267                if (vma->vm_start > start)
 268                        goto out;
 269                if (unlikely(grows & PROT_GROWSUP)) {
 270                        end = vma->vm_end;
 271                        error = -EINVAL;
 272                        if (!(vma->vm_flags & VM_GROWSUP))
 273                                goto out;
 274                }
 275        }
 276        if (start > vma->vm_start)
 277                prev = vma;
 278
 279        for (nstart = start ; ; ) {
 280                unsigned long newflags;
 281
 282                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 283
 284                newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 285
 286                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 287                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 288                        error = -EACCES;
 289                        goto out;
 290                }
 291
 292                error = security_file_mprotect(vma, reqprot, prot);
 293                if (error)
 294                        goto out;
 295
 296                tmp = vma->vm_end;
 297                if (tmp > end)
 298                        tmp = end;
 299                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 300                if (error)
 301                        goto out;
 302                perf_event_mmap(vma);
 303                nstart = tmp;
 304
 305                if (nstart < prev->vm_end)
 306                        nstart = prev->vm_end;
 307                if (nstart >= end)
 308                        goto out;
 309
 310                vma = prev->vm_next;
 311                if (!vma || vma->vm_start != nstart) {
 312                        error = -ENOMEM;
 313                        goto out;
 314                }
 315        }
 316out:
 317        up_write(&current->mm->mmap_sem);
 318        return error;
 319}
 320