mprotect: prevent alteration of the PAT bits
[linux-2.6.git] / 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 }