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