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/cacheflush.h>
  26 #include <asm/tlbflush.h>
  27
  28 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  29                 unsigned long addr, unsigned long end, pgprot_t newprot)
  30 {
  31         pte_t *pte;
  32         spinlock_t *ptl;
  33
  34         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  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_unlock(pte - 1, ptl);
  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         do {
  93                 next = pgd_addr_end(addr, end);
  94                 if (pgd_none_or_clear_bad(pgd))
  95                         continue;
  96                 change_pud_range(mm, pgd, addr, next, newprot);
  97         } while (pgd++, addr = next, addr != end);
  98         flush_tlb_range(vma, start, end);
  99 }
 100
 101 static int
 102 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 103         unsigned long start, unsigned long end, unsigned long newflags)
 104 {
 105         struct mm_struct *mm = vma->vm_mm;
 106         unsigned long oldflags = vma->vm_flags;
 107         long nrpages = (end - start) >> PAGE_SHIFT;
 108         unsigned long charged = 0;
 109         pgprot_t newprot;
 110         pgoff_t pgoff;
 111         int error;
 112
 113         if (newflags == oldflags) {
 114                 *pprev = vma;
 115                 return 0;
 116         }
 117
 118         /*
 119          * If we make a private mapping writable we increase our commit;
 120          * but (without finer accounting) cannot reduce our commit if we
 121          * make it unwritable again.
 122          *
 123          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 124          * a MAP_NORESERVE private mapping to writable will now reserve.
 125          */
 126         if (newflags & VM_WRITE) {
 127                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
 128                         charged = nrpages;
 129                         if (security_vm_enough_memory(charged))
 130                                 return -ENOMEM;
 131                         newflags |= VM_ACCOUNT;
 132                 }
 133         }
 134
 135         newprot = protection_map[newflags & 0xf];
 136
 137         /*
 138          * First try to merge with previous and/or next vma.
 139          */
 140         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 141         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 142                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 143         if (*pprev) {
 144                 vma = *pprev;
 145                 goto success;
 146         }
 147
 148         *pprev = vma;
 149
 150         if (start != vma->vm_start) {
 151                 error = split_vma(mm, vma, start, 1);
 152                 if (error)
 153                         goto fail;
 154         }
 155
 156         if (end != vma->vm_end) {
 157                 error = split_vma(mm, vma, end, 0);
 158                 if (error)
 159                         goto fail;
 160         }
 161
 162 success:
 163         /*
 164          * vm_flags and vm_page_prot are protected by the mmap_sem
 165          * held in write mode.
 166          */
 167         vma->vm_flags = newflags;
 168         vma->vm_page_prot = newprot;
 169         if (is_vm_hugetlb_page(vma))
 170                 hugetlb_change_protection(vma, start, end, newprot);
 171         else
 172                 change_protection(vma, start, end, newprot);
 173         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 174         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 175         return 0;
 176
 177 fail:
 178         vm_unacct_memory(charged);
 179         return error;
 180 }
 181
 182 asmlinkage long
 183 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 184 {
 185         unsigned long vm_flags, nstart, end, tmp, reqprot;
 186         struct vm_area_struct *vma, *prev;
 187         int error = -EINVAL;
 188         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 189         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 190         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 191                 return -EINVAL;
 192
 193         if (start & ~PAGE_MASK)
 194                 return -EINVAL;
 195         if (!len)
 196                 return 0;
 197         len = PAGE_ALIGN(len);
 198         end = start + len;
 199         if (end <= start)
 200                 return -ENOMEM;
 201         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 202                 return -EINVAL;
 203
 204         reqprot = prot;
 205         /*
 206          * Does the application expect PROT_READ to imply PROT_EXEC:
 207          */
 208         if (unlikely((prot & PROT_READ) &&
 209                         (current->personality & READ_IMPLIES_EXEC)))
 210                 prot |= PROT_EXEC;
 211
 212         vm_flags = calc_vm_prot_bits(prot);
 213
 214         down_write(&current->mm->mmap_sem);
 215
 216         vma = find_vma_prev(current->mm, start, &prev);
 217         error = -ENOMEM;
 218         if (!vma)
 219                 goto out;
 220         if (unlikely(grows & PROT_GROWSDOWN)) {
 221                 if (vma->vm_start >= end)
 222                         goto out;
 223                 start = vma->vm_start;
 224                 error = -EINVAL;
 225                 if (!(vma->vm_flags & VM_GROWSDOWN))
 226                         goto out;
 227         }
 228         else {
 229                 if (vma->vm_start > start)
 230                         goto out;
 231                 if (unlikely(grows & PROT_GROWSUP)) {
 232                         end = vma->vm_end;
 233                         error = -EINVAL;
 234                         if (!(vma->vm_flags & VM_GROWSUP))
 235                                 goto out;
 236                 }
 237         }
 238         if (start > vma->vm_start)
 239                 prev = vma;
 240
 241         for (nstart = start ; ; ) {
 242                 unsigned long newflags;
 243
 244                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 245
 246                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 247
 248                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 249                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 250                         error = -EACCES;
 251                         goto out;
 252                 }
 253
 254                 error = security_file_mprotect(vma, reqprot, prot);
 255                 if (error)
 256                         goto out;
 257
 258                 tmp = vma->vm_end;
 259                 if (tmp > end)
 260                         tmp = end;
 261                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 262                 if (error)
 263                         goto out;
 264                 nstart = tmp;
 265
 266                 if (nstart < prev->vm_end)
 267                         nstart = prev->vm_end;
 268                 if (nstart >= end)
 269                         goto out;
 270
 271                 vma = prev->vm_next;
 272                 if (!vma || vma->vm_start != nstart) {
 273                         error = -ENOMEM;
 274                         goto out;
 275                 }
 276         }
 277 out:
 278         up_write(&current->mm->mmap_sem);
 279         return error;
 280 }