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