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ksm: prevent mremap move poisoning
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CommitLineData
1da177e4
LT
1/*
2 * mm/mremap.c
3 *
4 * (C) Copyright 1996 Linus Torvalds
5 *
046c6884 6 * Address space accounting code <alan@lxorguk.ukuu.org.uk>
1da177e4
LT
7 * (C) Copyright 2002 Red Hat Inc, All Rights Reserved
8 */
9
10#include <linux/mm.h>
11#include <linux/hugetlb.h>
12#include <linux/slab.h>
13#include <linux/shm.h>
1ff82995 14#include <linux/ksm.h>
1da177e4
LT
15#include <linux/mman.h>
16#include <linux/swap.h>
c59ede7b 17#include <linux/capability.h>
1da177e4
LT
18#include <linux/fs.h>
19#include <linux/highmem.h>
20#include <linux/security.h>
21#include <linux/syscalls.h>
cddb8a5c 22#include <linux/mmu_notifier.h>
1da177e4
LT
23
24#include <asm/uaccess.h>
25#include <asm/cacheflush.h>
26#include <asm/tlbflush.h>
27
ba470de4
RR
28#include "internal.h"
29
7be7a546 30static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
1da177e4
LT
31{
32 pgd_t *pgd;
33 pud_t *pud;
34 pmd_t *pmd;
35
36 pgd = pgd_offset(mm, addr);
37 if (pgd_none_or_clear_bad(pgd))
38 return NULL;
39
40 pud = pud_offset(pgd, addr);
41 if (pud_none_or_clear_bad(pud))
42 return NULL;
43
44 pmd = pmd_offset(pud, addr);
45 if (pmd_none_or_clear_bad(pmd))
46 return NULL;
47
7be7a546 48 return pmd;
1da177e4
LT
49}
50
7be7a546 51static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
1da177e4
LT
52{
53 pgd_t *pgd;
54 pud_t *pud;
c74df32c 55 pmd_t *pmd;
1da177e4
LT
56
57 pgd = pgd_offset(mm, addr);
1da177e4
LT
58 pud = pud_alloc(mm, pgd, addr);
59 if (!pud)
c74df32c 60 return NULL;
7be7a546 61
1da177e4 62 pmd = pmd_alloc(mm, pud, addr);
7be7a546 63 if (!pmd)
c74df32c 64 return NULL;
7be7a546 65
1bb3630e 66 if (!pmd_present(*pmd) && __pte_alloc(mm, pmd, addr))
c74df32c
HD
67 return NULL;
68
7be7a546 69 return pmd;
1da177e4
LT
70}
71
7be7a546
HD
72static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
73 unsigned long old_addr, unsigned long old_end,
74 struct vm_area_struct *new_vma, pmd_t *new_pmd,
75 unsigned long new_addr)
1da177e4
LT
76{
77 struct address_space *mapping = NULL;
78 struct mm_struct *mm = vma->vm_mm;
7be7a546 79 pte_t *old_pte, *new_pte, pte;
4c21e2f2 80 spinlock_t *old_ptl, *new_ptl;
cddb8a5c 81 unsigned long old_start;
1da177e4 82
cddb8a5c
AA
83 old_start = old_addr;
84 mmu_notifier_invalidate_range_start(vma->vm_mm,
85 old_start, old_end);
1da177e4
LT
86 if (vma->vm_file) {
87 /*
88 * Subtle point from Rajesh Venkatasubramanian: before
89 * moving file-based ptes, we must lock vmtruncate out,
90 * since it might clean the dst vma before the src vma,
91 * and we propagate stale pages into the dst afterward.
92 */
93 mapping = vma->vm_file->f_mapping;
94 spin_lock(&mapping->i_mmap_lock);
95 if (new_vma->vm_truncate_count &&
96 new_vma->vm_truncate_count != vma->vm_truncate_count)
97 new_vma->vm_truncate_count = 0;
98 }
1da177e4 99
4c21e2f2
HD
100 /*
101 * We don't have to worry about the ordering of src and dst
102 * pte locks because exclusive mmap_sem prevents deadlock.
103 */
c74df32c
HD
104 old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
105 new_pte = pte_offset_map_nested(new_pmd, new_addr);
4c21e2f2
HD
106 new_ptl = pte_lockptr(mm, new_pmd);
107 if (new_ptl != old_ptl)
f20dc5f7 108 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
6606c3e0 109 arch_enter_lazy_mmu_mode();
7be7a546
HD
110
111 for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
112 new_pte++, new_addr += PAGE_SIZE) {
113 if (pte_none(*old_pte))
114 continue;
115 pte = ptep_clear_flush(vma, old_addr, old_pte);
7be7a546
HD
116 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
117 set_pte_at(mm, new_addr, new_pte, pte);
1da177e4 118 }
7be7a546 119
6606c3e0 120 arch_leave_lazy_mmu_mode();
4c21e2f2
HD
121 if (new_ptl != old_ptl)
122 spin_unlock(new_ptl);
7be7a546 123 pte_unmap_nested(new_pte - 1);
c74df32c 124 pte_unmap_unlock(old_pte - 1, old_ptl);
1da177e4
LT
125 if (mapping)
126 spin_unlock(&mapping->i_mmap_lock);
cddb8a5c 127 mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
1da177e4
LT
128}
129
7be7a546
HD
130#define LATENCY_LIMIT (64 * PAGE_SIZE)
131
b6a2fea3 132unsigned long move_page_tables(struct vm_area_struct *vma,
1da177e4
LT
133 unsigned long old_addr, struct vm_area_struct *new_vma,
134 unsigned long new_addr, unsigned long len)
135{
7be7a546
HD
136 unsigned long extent, next, old_end;
137 pmd_t *old_pmd, *new_pmd;
1da177e4 138
7be7a546
HD
139 old_end = old_addr + len;
140 flush_cache_range(vma, old_addr, old_end);
1da177e4 141
7be7a546 142 for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
1da177e4 143 cond_resched();
7be7a546
HD
144 next = (old_addr + PMD_SIZE) & PMD_MASK;
145 if (next - 1 > old_end)
146 next = old_end;
147 extent = next - old_addr;
148 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
149 if (!old_pmd)
150 continue;
151 new_pmd = alloc_new_pmd(vma->vm_mm, new_addr);
152 if (!new_pmd)
153 break;
154 next = (new_addr + PMD_SIZE) & PMD_MASK;
155 if (extent > next - new_addr)
156 extent = next - new_addr;
157 if (extent > LATENCY_LIMIT)
158 extent = LATENCY_LIMIT;
159 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
160 new_vma, new_pmd, new_addr);
1da177e4 161 }
7be7a546
HD
162
163 return len + old_addr - old_end; /* how much done */
1da177e4
LT
164}
165
166static unsigned long move_vma(struct vm_area_struct *vma,
167 unsigned long old_addr, unsigned long old_len,
168 unsigned long new_len, unsigned long new_addr)
169{
170 struct mm_struct *mm = vma->vm_mm;
171 struct vm_area_struct *new_vma;
172 unsigned long vm_flags = vma->vm_flags;
173 unsigned long new_pgoff;
174 unsigned long moved_len;
175 unsigned long excess = 0;
365e9c87 176 unsigned long hiwater_vm;
1da177e4
LT
177 int split = 0;
178
179 /*
180 * We'd prefer to avoid failure later on in do_munmap:
181 * which may split one vma into three before unmapping.
182 */
183 if (mm->map_count >= sysctl_max_map_count - 3)
184 return -ENOMEM;
185
1ff82995
HD
186 /*
187 * Advise KSM to break any KSM pages in the area to be moved:
188 * it would be confusing if they were to turn up at the new
189 * location, where they happen to coincide with different KSM
190 * pages recently unmapped. But leave vma->vm_flags as it was,
191 * so KSM can come around to merge on vma and new_vma afterwards.
192 */
193 if (ksm_madvise(vma, old_addr, old_addr + old_len,
194 MADV_UNMERGEABLE, &vm_flags))
195 return -ENOMEM;
196
1da177e4
LT
197 new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
198 new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff);
199 if (!new_vma)
200 return -ENOMEM;
201
202 moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len);
203 if (moved_len < old_len) {
204 /*
205 * On error, move entries back from new area to old,
206 * which will succeed since page tables still there,
207 * and then proceed to unmap new area instead of old.
208 */
209 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len);
210 vma = new_vma;
211 old_len = new_len;
212 old_addr = new_addr;
213 new_addr = -ENOMEM;
214 }
215
216 /* Conceal VM_ACCOUNT so old reservation is not undone */
217 if (vm_flags & VM_ACCOUNT) {
218 vma->vm_flags &= ~VM_ACCOUNT;
219 excess = vma->vm_end - vma->vm_start - old_len;
220 if (old_addr > vma->vm_start &&
221 old_addr + old_len < vma->vm_end)
222 split = 1;
223 }
224
71799062 225 /*
365e9c87
HD
226 * If we failed to move page tables we still do total_vm increment
227 * since do_munmap() will decrement it by old_len == new_len.
228 *
229 * Since total_vm is about to be raised artificially high for a
230 * moment, we need to restore high watermark afterwards: if stats
231 * are taken meanwhile, total_vm and hiwater_vm appear too high.
232 * If this were a serious issue, we'd add a flag to do_munmap().
71799062 233 */
365e9c87 234 hiwater_vm = mm->hiwater_vm;
71799062 235 mm->total_vm += new_len >> PAGE_SHIFT;
ab50b8ed 236 vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
71799062 237
1da177e4
LT
238 if (do_munmap(mm, old_addr, old_len) < 0) {
239 /* OOM: unable to split vma, just get accounts right */
240 vm_unacct_memory(excess >> PAGE_SHIFT);
241 excess = 0;
242 }
365e9c87 243 mm->hiwater_vm = hiwater_vm;
1da177e4
LT
244
245 /* Restore VM_ACCOUNT if one or two pieces of vma left */
246 if (excess) {
247 vma->vm_flags |= VM_ACCOUNT;
248 if (split)
249 vma->vm_next->vm_flags |= VM_ACCOUNT;
250 }
251
1da177e4
LT
252 if (vm_flags & VM_LOCKED) {
253 mm->locked_vm += new_len >> PAGE_SHIFT;
254 if (new_len > old_len)
ba470de4
RR
255 mlock_vma_pages_range(new_vma, new_addr + old_len,
256 new_addr + new_len);
1da177e4
LT
257 }
258
259 return new_addr;
260}
261
262/*
263 * Expand (or shrink) an existing mapping, potentially moving it at the
264 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
265 *
266 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
267 * This option implies MREMAP_MAYMOVE.
268 */
269unsigned long do_mremap(unsigned long addr,
270 unsigned long old_len, unsigned long new_len,
271 unsigned long flags, unsigned long new_addr)
272{
d0de32d9 273 struct mm_struct *mm = current->mm;
1da177e4
LT
274 struct vm_area_struct *vma;
275 unsigned long ret = -EINVAL;
276 unsigned long charged = 0;
277
278 if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
279 goto out;
280
281 if (addr & ~PAGE_MASK)
282 goto out;
283
284 old_len = PAGE_ALIGN(old_len);
285 new_len = PAGE_ALIGN(new_len);
286
287 /*
288 * We allow a zero old-len as a special case
289 * for DOS-emu "duplicate shm area" thing. But
290 * a zero new-len is nonsensical.
291 */
292 if (!new_len)
293 goto out;
294
295 /* new_addr is only valid if MREMAP_FIXED is specified */
296 if (flags & MREMAP_FIXED) {
297 if (new_addr & ~PAGE_MASK)
298 goto out;
299 if (!(flags & MREMAP_MAYMOVE))
300 goto out;
301
302 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
303 goto out;
304
305 /* Check if the location we're moving into overlaps the
306 * old location at all, and fail if it does.
307 */
308 if ((new_addr <= addr) && (new_addr+new_len) > addr)
309 goto out;
310
311 if ((addr <= new_addr) && (addr+old_len) > new_addr)
312 goto out;
313
c80544dc 314 ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
ed032189
EP
315 if (ret)
316 goto out;
317
d0de32d9 318 ret = do_munmap(mm, new_addr, new_len);
1da177e4
LT
319 if (ret)
320 goto out;
321 }
322
323 /*
324 * Always allow a shrinking remap: that just unmaps
325 * the unnecessary pages..
326 * do_munmap does all the needed commit accounting
327 */
328 if (old_len >= new_len) {
d0de32d9 329 ret = do_munmap(mm, addr+new_len, old_len - new_len);
1da177e4
LT
330 if (ret && old_len != new_len)
331 goto out;
332 ret = addr;
333 if (!(flags & MREMAP_FIXED) || (new_addr == addr))
334 goto out;
335 old_len = new_len;
336 }
337
338 /*
339 * Ok, we need to grow.. or relocate.
340 */
341 ret = -EFAULT;
d0de32d9 342 vma = find_vma(mm, addr);
1da177e4
LT
343 if (!vma || vma->vm_start > addr)
344 goto out;
345 if (is_vm_hugetlb_page(vma)) {
346 ret = -EINVAL;
347 goto out;
348 }
349 /* We can't remap across vm area boundaries */
350 if (old_len > vma->vm_end - addr)
351 goto out;
4d7672b4 352 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) {
1da177e4
LT
353 if (new_len > old_len)
354 goto out;
355 }
356 if (vma->vm_flags & VM_LOCKED) {
357 unsigned long locked, lock_limit;
d0de32d9 358 locked = mm->locked_vm << PAGE_SHIFT;
1da177e4
LT
359 lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
360 locked += new_len - old_len;
361 ret = -EAGAIN;
362 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
363 goto out;
364 }
d0de32d9 365 if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT)) {
119f657c 366 ret = -ENOMEM;
1da177e4 367 goto out;
119f657c 368 }
1da177e4
LT
369
370 if (vma->vm_flags & VM_ACCOUNT) {
371 charged = (new_len - old_len) >> PAGE_SHIFT;
372 if (security_vm_enough_memory(charged))
373 goto out_nc;
374 }
375
376 /* old_len exactly to the end of the area..
377 * And we're not relocating the area.
378 */
379 if (old_len == vma->vm_end - addr &&
380 !((flags & MREMAP_FIXED) && (addr != new_addr)) &&
381 (old_len != new_len || !(flags & MREMAP_MAYMOVE))) {
382 unsigned long max_addr = TASK_SIZE;
383 if (vma->vm_next)
384 max_addr = vma->vm_next->vm_start;
385 /* can we just expand the current mapping? */
386 if (max_addr - addr >= new_len) {
387 int pages = (new_len - old_len) >> PAGE_SHIFT;
388
389 vma_adjust(vma, vma->vm_start,
390 addr + new_len, vma->vm_pgoff, NULL);
391
d0de32d9
HD
392 mm->total_vm += pages;
393 vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
1da177e4 394 if (vma->vm_flags & VM_LOCKED) {
d0de32d9 395 mm->locked_vm += pages;
ba470de4 396 mlock_vma_pages_range(vma, addr + old_len,
1da177e4
LT
397 addr + new_len);
398 }
399 ret = addr;
400 goto out;
401 }
402 }
403
404 /*
405 * We weren't able to just expand or shrink the area,
406 * we need to create a new one and move it..
407 */
408 ret = -ENOMEM;
409 if (flags & MREMAP_MAYMOVE) {
410 if (!(flags & MREMAP_FIXED)) {
411 unsigned long map_flags = 0;
412 if (vma->vm_flags & VM_MAYSHARE)
413 map_flags |= MAP_SHARED;
414
415 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
416 vma->vm_pgoff, map_flags);
ed032189
EP
417 if (new_addr & ~PAGE_MASK) {
418 ret = new_addr;
419 goto out;
420 }
421
c80544dc 422 ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
ed032189 423 if (ret)
1da177e4
LT
424 goto out;
425 }
426 ret = move_vma(vma, addr, old_len, new_len, new_addr);
427 }
428out:
429 if (ret & ~PAGE_MASK)
430 vm_unacct_memory(charged);
431out_nc:
432 return ret;
433}
434
6a6160a7
HC
435SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
436 unsigned long, new_len, unsigned long, flags,
437 unsigned long, new_addr)
1da177e4
LT
438{
439 unsigned long ret;
440
441 down_write(&current->mm->mmap_sem);
442 ret = do_mremap(addr, old_len, new_len, flags, new_addr);
443 up_write(&current->mm->mmap_sem);
444 return ret;
445}