lib/iov_iter.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <crypto/hash.h>
   3 #include <linux/export.h>
   4 #include <linux/bvec.h>
   5 #include <linux/fault-inject-usercopy.h>
   6 #include <linux/uio.h>
   7 #include <linux/pagemap.h>
   8 #include <linux/highmem.h>
   9 #include <linux/slab.h>
  10 #include <linux/vmalloc.h>
  11 #include <linux/splice.h>
  12 #include <linux/compat.h>
  13 #include <net/checksum.h>
  14 #include <linux/scatterlist.h>
  15 #include <linux/instrumented.h>
  16
  17 /* covers ubuf and kbuf alike */
  18 #define iterate_buf(i, n, base, len, off, __p, STEP) {          \
  19         size_t __maybe_unused off = 0;                          \
  20         len = n;                                                \
  21         base = __p + i->iov_offset;                             \
  22         len -= (STEP);                                          \
  23         i->iov_offset += len;                                   \
  24         n = len;                                                \
  25 }
  26
  27 /* covers iovec and kvec alike */
  28 #define iterate_iovec(i, n, base, len, off, __p, STEP) {        \
  29         size_t off = 0;                                         \
  30         size_t skip = i->iov_offset;                            \
  31         do {                                                    \
  32                 len = min(n, __p->iov_len - skip);              \
  33                 if (likely(len)) {                              \
  34                         base = __p->iov_base + skip;            \
  35                         len -= (STEP);                          \
  36                         off += len;                             \
  37                         skip += len;                            \
  38                         n -= len;                               \
  39                         if (skip < __p->iov_len)                \
  40                                 break;                          \
  41                 }                                               \
  42                 __p++;                                          \
  43                 skip = 0;                                       \
  44         } while (n);                                            \
  45         i->iov_offset = skip;                                   \
  46         n = off;                                                \
  47 }
  48
  49 #define iterate_bvec(i, n, base, len, off, p, STEP) {           \
  50         size_t off = 0;                                         \
  51         unsigned skip = i->iov_offset;                          \
  52         while (n) {                                             \
  53                 unsigned offset = p->bv_offset + skip;          \
  54                 unsigned left;                                  \
  55                 void *kaddr = kmap_local_page(p->bv_page +      \
  56                                         offset / PAGE_SIZE);    \
  57                 base = kaddr + offset % PAGE_SIZE;              \
  58                 len = min(min(n, (size_t)(p->bv_len - skip)),   \
  59                      (size_t)(PAGE_SIZE - offset % PAGE_SIZE)); \
  60                 left = (STEP);                                  \
  61                 kunmap_local(kaddr);                            \
  62                 len -= left;                                    \
  63                 off += len;                                     \
  64                 skip += len;                                    \
  65                 if (skip == p->bv_len) {                        \
  66                         skip = 0;                               \
  67                         p++;                                    \
  68                 }                                               \
  69                 n -= len;                                       \
  70                 if (left)                                       \
  71                         break;                                  \
  72         }                                                       \
  73         i->iov_offset = skip;                                   \
  74         n = off;                                                \
  75 }
  76
  77 #define iterate_xarray(i, n, base, len, __off, STEP) {          \
  78         __label__ __out;                                        \
  79         size_t __off = 0;                                       \
  80         struct folio *folio;                                    \
  81         loff_t start = i->xarray_start + i->iov_offset;         \
  82         pgoff_t index = start / PAGE_SIZE;                      \
  83         XA_STATE(xas, i->xarray, index);                        \
  84                                                                 \
  85         len = PAGE_SIZE - offset_in_page(start);                \
  86         rcu_read_lock();                                        \
  87         xas_for_each(&xas, folio, ULONG_MAX) {                  \
  88                 unsigned left;                                  \
  89                 size_t offset;                                  \
  90                 if (xas_retry(&xas, folio))                     \
  91                         continue;                               \
  92                 if (WARN_ON(xa_is_value(folio)))                \
  93                         break;                                  \
  94                 if (WARN_ON(folio_test_hugetlb(folio)))         \
  95                         break;                                  \
  96                 offset = offset_in_folio(folio, start + __off); \
  97                 while (offset < folio_size(folio)) {            \
  98                         base = kmap_local_folio(folio, offset); \
  99                         len = min(n, len);                      \
 100                         left = (STEP);                          \
 101                         kunmap_local(base);                     \
 102                         len -= left;                            \
 103                         __off += len;                           \
 104                         n -= len;                               \
 105                         if (left || n == 0)                     \
 106                                 goto __out;                     \
 107                         offset += len;                          \
 108                         len = PAGE_SIZE;                        \
 109                 }                                               \
 110         }                                                       \
 111 __out:                                                          \
 112         rcu_read_unlock();                                      \
 113         i->iov_offset += __off;                                 \
 114         n = __off;                                              \
 115 }
 116
 117 #define __iterate_and_advance(i, n, base, len, off, I, K) {     \
 118         if (unlikely(i->count < n))                             \
 119                 n = i->count;                                   \
 120         if (likely(n)) {                                        \
 121                 if (likely(iter_is_ubuf(i))) {                  \
 122                         void __user *base;                      \
 123                         size_t len;                             \
 124                         iterate_buf(i, n, base, len, off,       \
 125                                                 i->ubuf, (I))   \
 126                 } else if (likely(iter_is_iovec(i))) {          \
 127                         const struct iovec *iov = iter_iov(i);  \
 128                         void __user *base;                      \
 129                         size_t len;                             \
 130                         iterate_iovec(i, n, base, len, off,     \
 131                                                 iov, (I))       \
 132                         i->nr_segs -= iov - iter_iov(i);        \
 133                         i->__iov = iov;                         \
 134                 } else if (iov_iter_is_bvec(i)) {               \
 135                         const struct bio_vec *bvec = i->bvec;   \
 136                         void *base;                             \
 137                         size_t len;                             \
 138                         iterate_bvec(i, n, base, len, off,      \
 139                                                 bvec, (K))      \
 140                         i->nr_segs -= bvec - i->bvec;           \
 141                         i->bvec = bvec;                         \
 142                 } else if (iov_iter_is_kvec(i)) {               \
 143                         const struct kvec *kvec = i->kvec;      \
 144                         void *base;                             \
 145                         size_t len;                             \
 146                         iterate_iovec(i, n, base, len, off,     \
 147                                                 kvec, (K))      \
 148                         i->nr_segs -= kvec - i->kvec;           \
 149                         i->kvec = kvec;                         \
 150                 } else if (iov_iter_is_xarray(i)) {             \
 151                         void *base;                             \
 152                         size_t len;                             \
 153                         iterate_xarray(i, n, base, len, off,    \
 154                                                         (K))    \
 155                 }                                               \
 156                 i->count -= n;                                  \
 157         }                                                       \
 158 }
 159 #define iterate_and_advance(i, n, base, len, off, I, K) \
 160         __iterate_and_advance(i, n, base, len, off, I, ((void)(K),0))
 161
 162 static int copyout(void __user *to, const void *from, size_t n)
 163 {
 164         if (should_fail_usercopy())
 165                 return n;
 166         if (access_ok(to, n)) {
 167                 instrument_copy_to_user(to, from, n);
 168                 n = raw_copy_to_user(to, from, n);
 169         }
 170         return n;
 171 }
 172
 173 static int copyout_nofault(void __user *to, const void *from, size_t n)
 174 {
 175         long res;
 176
 177         if (should_fail_usercopy())
 178                 return n;
 179
 180         res = copy_to_user_nofault(to, from, n);
 181
 182         return res < 0 ? n : res;
 183 }
 184
 185 static int copyin(void *to, const void __user *from, size_t n)
 186 {
 187         size_t res = n;
 188
 189         if (should_fail_usercopy())
 190                 return n;
 191         if (access_ok(from, n)) {
 192                 instrument_copy_from_user_before(to, from, n);
 193                 res = raw_copy_from_user(to, from, n);
 194                 instrument_copy_from_user_after(to, from, n, res);
 195         }
 196         return res;
 197 }
 198
 199 /*
 200  * fault_in_iov_iter_readable - fault in iov iterator for reading
 201  * @i: iterator
 202  * @size: maximum length
 203  *
 204  * Fault in one or more iovecs of the given iov_iter, to a maximum length of
 205  * @size.  For each iovec, fault in each page that constitutes the iovec.
 206  *
 207  * Returns the number of bytes not faulted in (like copy_to_user() and
 208  * copy_from_user()).
 209  *
 210  * Always returns 0 for non-userspace iterators.
 211  */
 212 size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t size)
 213 {
 214         if (iter_is_ubuf(i)) {
 215                 size_t n = min(size, iov_iter_count(i));
 216                 n -= fault_in_readable(i->ubuf + i->iov_offset, n);
 217                 return size - n;
 218         } else if (iter_is_iovec(i)) {
 219                 size_t count = min(size, iov_iter_count(i));
 220                 const struct iovec *p;
 221                 size_t skip;
 222
 223                 size -= count;
 224                 for (p = iter_iov(i), skip = i->iov_offset; count; p++, skip = 0) {
 225                         size_t len = min(count, p->iov_len - skip);
 226                         size_t ret;
 227
 228                         if (unlikely(!len))
 229                                 continue;
 230                         ret = fault_in_readable(p->iov_base + skip, len);
 231                         count -= len - ret;
 232                         if (ret)
 233                                 break;
 234                 }
 235                 return count + size;
 236         }
 237         return 0;
 238 }
 239 EXPORT_SYMBOL(fault_in_iov_iter_readable);
 240
 241 /*
 242  * fault_in_iov_iter_writeable - fault in iov iterator for writing
 243  * @i: iterator
 244  * @size: maximum length
 245  *
 246  * Faults in the iterator using get_user_pages(), i.e., without triggering
 247  * hardware page faults.  This is primarily useful when we already know that
 248  * some or all of the pages in @i aren't in memory.
 249  *
 250  * Returns the number of bytes not faulted in, like copy_to_user() and
 251  * copy_from_user().
 252  *
 253  * Always returns 0 for non-user-space iterators.
 254  */
 255 size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t size)
 256 {
 257         if (iter_is_ubuf(i)) {
 258                 size_t n = min(size, iov_iter_count(i));
 259                 n -= fault_in_safe_writeable(i->ubuf + i->iov_offset, n);
 260                 return size - n;
 261         } else if (iter_is_iovec(i)) {
 262                 size_t count = min(size, iov_iter_count(i));
 263                 const struct iovec *p;
 264                 size_t skip;
 265
 266                 size -= count;
 267                 for (p = iter_iov(i), skip = i->iov_offset; count; p++, skip = 0) {
 268                         size_t len = min(count, p->iov_len - skip);
 269                         size_t ret;
 270
 271                         if (unlikely(!len))
 272                                 continue;
 273                         ret = fault_in_safe_writeable(p->iov_base + skip, len);
 274                         count -= len - ret;
 275                         if (ret)
 276                                 break;
 277                 }
 278                 return count + size;
 279         }
 280         return 0;
 281 }
 282 EXPORT_SYMBOL(fault_in_iov_iter_writeable);
 283
 284 void iov_iter_init(struct iov_iter *i, unsigned int direction,
 285                         const struct iovec *iov, unsigned long nr_segs,
 286                         size_t count)
 287 {
 288         WARN_ON(direction & ~(READ | WRITE));
 289         *i = (struct iov_iter) {
 290                 .iter_type = ITER_IOVEC,
 291                 .copy_mc = false,
 292                 .nofault = false,
 293                 .user_backed = true,
 294                 .data_source = direction,
 295                 .__iov = iov,
 296                 .nr_segs = nr_segs,
 297                 .iov_offset = 0,
 298                 .count = count
 299         };
 300 }
 301 EXPORT_SYMBOL(iov_iter_init);
 302
 303 static __wsum csum_and_memcpy(void *to, const void *from, size_t len,
 304                               __wsum sum, size_t off)
 305 {
 306         __wsum next = csum_partial_copy_nocheck(from, to, len);
 307         return csum_block_add(sum, next, off);
 308 }
 309
 310 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 311 {
 312         if (WARN_ON_ONCE(i->data_source))
 313                 return 0;
 314         if (user_backed_iter(i))
 315                 might_fault();
 316         iterate_and_advance(i, bytes, base, len, off,
 317                 copyout(base, addr + off, len),
 318                 memcpy(base, addr + off, len)
 319         )
 320
 321         return bytes;
 322 }
 323 EXPORT_SYMBOL(_copy_to_iter);
 324
 325 #ifdef CONFIG_ARCH_HAS_COPY_MC
 326 static int copyout_mc(void __user *to, const void *from, size_t n)
 327 {
 328         if (access_ok(to, n)) {
 329                 instrument_copy_to_user(to, from, n);
 330                 n = copy_mc_to_user((__force void *) to, from, n);
 331         }
 332         return n;
 333 }
 334
 335 /**
 336  * _copy_mc_to_iter - copy to iter with source memory error exception handling
 337  * @addr: source kernel address
 338  * @bytes: total transfer length
 339  * @i: destination iterator
 340  *
 341  * The pmem driver deploys this for the dax operation
 342  * (dax_copy_to_iter()) for dax reads (bypass page-cache and the
 343  * block-layer). Upon #MC read(2) aborts and returns EIO or the bytes
 344  * successfully copied.
 345  *
 346  * The main differences between this and typical _copy_to_iter().
 347  *
 348  * * Typical tail/residue handling after a fault retries the copy
 349  *   byte-by-byte until the fault happens again. Re-triggering machine
 350  *   checks is potentially fatal so the implementation uses source
 351  *   alignment and poison alignment assumptions to avoid re-triggering
 352  *   hardware exceptions.
 353  *
 354  * * ITER_KVEC and ITER_BVEC can return short copies.  Compare to
 355  *   copy_to_iter() where only ITER_IOVEC attempts might return a short copy.
 356  *
 357  * Return: number of bytes copied (may be %0)
 358  */
 359 size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 360 {
 361         if (WARN_ON_ONCE(i->data_source))
 362                 return 0;
 363         if (user_backed_iter(i))
 364                 might_fault();
 365         __iterate_and_advance(i, bytes, base, len, off,
 366                 copyout_mc(base, addr + off, len),
 367                 copy_mc_to_kernel(base, addr + off, len)
 368         )
 369
 370         return bytes;
 371 }
 372 EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
 373 #endif /* CONFIG_ARCH_HAS_COPY_MC */
 374
 375 static void *memcpy_from_iter(struct iov_iter *i, void *to, const void *from,
 376                                  size_t size)
 377 {
 378         if (iov_iter_is_copy_mc(i))
 379                 return (void *)copy_mc_to_kernel(to, from, size);
 380         return memcpy(to, from, size);
 381 }
 382
 383 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 384 {
 385         if (WARN_ON_ONCE(!i->data_source))
 386                 return 0;
 387
 388         if (user_backed_iter(i))
 389                 might_fault();
 390         iterate_and_advance(i, bytes, base, len, off,
 391                 copyin(addr + off, base, len),
 392                 memcpy_from_iter(i, addr + off, base, len)
 393         )
 394
 395         return bytes;
 396 }
 397 EXPORT_SYMBOL(_copy_from_iter);
 398
 399 size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 400 {
 401         if (WARN_ON_ONCE(!i->data_source))
 402                 return 0;
 403
 404         iterate_and_advance(i, bytes, base, len, off,
 405                 __copy_from_user_inatomic_nocache(addr + off, base, len),
 406                 memcpy(addr + off, base, len)
 407         )
 408
 409         return bytes;
 410 }
 411 EXPORT_SYMBOL(_copy_from_iter_nocache);
 412
 413 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
 414 /**
 415  * _copy_from_iter_flushcache - write destination through cpu cache
 416  * @addr: destination kernel address
 417  * @bytes: total transfer length
 418  * @i: source iterator
 419  *
 420  * The pmem driver arranges for filesystem-dax to use this facility via
 421  * dax_copy_from_iter() for ensuring that writes to persistent memory
 422  * are flushed through the CPU cache. It is differentiated from
 423  * _copy_from_iter_nocache() in that guarantees all data is flushed for
 424  * all iterator types. The _copy_from_iter_nocache() only attempts to
 425  * bypass the cache for the ITER_IOVEC case, and on some archs may use
 426  * instructions that strand dirty-data in the cache.
 427  *
 428  * Return: number of bytes copied (may be %0)
 429  */
 430 size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
 431 {
 432         if (WARN_ON_ONCE(!i->data_source))
 433                 return 0;
 434
 435         iterate_and_advance(i, bytes, base, len, off,
 436                 __copy_from_user_flushcache(addr + off, base, len),
 437                 memcpy_flushcache(addr + off, base, len)
 438         )
 439
 440         return bytes;
 441 }
 442 EXPORT_SYMBOL_GPL(_copy_from_iter_flushcache);
 443 #endif
 444
 445 static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
 446 {
 447         struct page *head;
 448         size_t v = n + offset;
 449
 450         /*
 451          * The general case needs to access the page order in order
 452          * to compute the page size.
 453          * However, we mostly deal with order-0 pages and thus can
 454          * avoid a possible cache line miss for requests that fit all
 455          * page orders.
 456          */
 457         if (n <= v && v <= PAGE_SIZE)
 458                 return true;
 459
 460         head = compound_head(page);
 461         v += (page - head) << PAGE_SHIFT;
 462
 463         if (WARN_ON(n > v || v > page_size(head)))
 464                 return false;
 465         return true;
 466 }
 467
 468 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 469                          struct iov_iter *i)
 470 {
 471         size_t res = 0;
 472         if (!page_copy_sane(page, offset, bytes))
 473                 return 0;
 474         if (WARN_ON_ONCE(i->data_source))
 475                 return 0;
 476         page += offset / PAGE_SIZE; // first subpage
 477         offset %= PAGE_SIZE;
 478         while (1) {
 479                 void *kaddr = kmap_local_page(page);
 480                 size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
 481                 n = _copy_to_iter(kaddr + offset, n, i);
 482                 kunmap_local(kaddr);
 483                 res += n;
 484                 bytes -= n;
 485                 if (!bytes || !n)
 486                         break;
 487                 offset += n;
 488                 if (offset == PAGE_SIZE) {
 489                         page++;
 490                         offset = 0;
 491                 }
 492         }
 493         return res;
 494 }
 495 EXPORT_SYMBOL(copy_page_to_iter);
 496
 497 size_t copy_page_to_iter_nofault(struct page *page, unsigned offset, size_t bytes,
 498                                  struct iov_iter *i)
 499 {
 500         size_t res = 0;
 501
 502         if (!page_copy_sane(page, offset, bytes))
 503                 return 0;
 504         if (WARN_ON_ONCE(i->data_source))
 505                 return 0;
 506         page += offset / PAGE_SIZE; // first subpage
 507         offset %= PAGE_SIZE;
 508         while (1) {
 509                 void *kaddr = kmap_local_page(page);
 510                 size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
 511
 512                 iterate_and_advance(i, n, base, len, off,
 513                         copyout_nofault(base, kaddr + offset + off, len),
 514                         memcpy(base, kaddr + offset + off, len)
 515                 )
 516                 kunmap_local(kaddr);
 517                 res += n;
 518                 bytes -= n;
 519                 if (!bytes || !n)
 520                         break;
 521                 offset += n;
 522                 if (offset == PAGE_SIZE) {
 523                         page++;
 524                         offset = 0;
 525                 }
 526         }
 527         return res;
 528 }
 529 EXPORT_SYMBOL(copy_page_to_iter_nofault);
 530
 531 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 532                          struct iov_iter *i)
 533 {
 534         size_t res = 0;
 535         if (!page_copy_sane(page, offset, bytes))
 536                 return 0;
 537         page += offset / PAGE_SIZE; // first subpage
 538         offset %= PAGE_SIZE;
 539         while (1) {
 540                 void *kaddr = kmap_local_page(page);
 541                 size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
 542                 n = _copy_from_iter(kaddr + offset, n, i);
 543                 kunmap_local(kaddr);
 544                 res += n;
 545                 bytes -= n;
 546                 if (!bytes || !n)
 547                         break;
 548                 offset += n;
 549                 if (offset == PAGE_SIZE) {
 550                         page++;
 551                         offset = 0;
 552                 }
 553         }
 554         return res;
 555 }
 556 EXPORT_SYMBOL(copy_page_from_iter);
 557
 558 size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 559 {
 560         iterate_and_advance(i, bytes, base, len, count,
 561                 clear_user(base, len),
 562                 memset(base, 0, len)
 563         )
 564
 565         return bytes;
 566 }
 567 EXPORT_SYMBOL(iov_iter_zero);
 568
 569 size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t bytes,
 570                                   struct iov_iter *i)
 571 {
 572         char *kaddr = kmap_atomic(page), *p = kaddr + offset;
 573         if (!page_copy_sane(page, offset, bytes)) {
 574                 kunmap_atomic(kaddr);
 575                 return 0;
 576         }
 577         if (WARN_ON_ONCE(!i->data_source)) {
 578                 kunmap_atomic(kaddr);
 579                 return 0;
 580         }
 581         iterate_and_advance(i, bytes, base, len, off,
 582                 copyin(p + off, base, len),
 583                 memcpy_from_iter(i, p + off, base, len)
 584         )
 585         kunmap_atomic(kaddr);
 586         return bytes;
 587 }
 588 EXPORT_SYMBOL(copy_page_from_iter_atomic);
 589
 590 static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
 591 {
 592         const struct bio_vec *bvec, *end;
 593
 594         if (!i->count)
 595                 return;
 596         i->count -= size;
 597
 598         size += i->iov_offset;
 599
 600         for (bvec = i->bvec, end = bvec + i->nr_segs; bvec < end; bvec++) {
 601                 if (likely(size < bvec->bv_len))
 602                         break;
 603                 size -= bvec->bv_len;
 604         }
 605         i->iov_offset = size;
 606         i->nr_segs -= bvec - i->bvec;
 607         i->bvec = bvec;
 608 }
 609
 610 static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
 611 {
 612         const struct iovec *iov, *end;
 613
 614         if (!i->count)
 615                 return;
 616         i->count -= size;
 617
 618         size += i->iov_offset; // from beginning of current segment
 619         for (iov = iter_iov(i), end = iov + i->nr_segs; iov < end; iov++) {
 620                 if (likely(size < iov->iov_len))
 621                         break;
 622                 size -= iov->iov_len;
 623         }
 624         i->iov_offset = size;
 625         i->nr_segs -= iov - iter_iov(i);
 626         i->__iov = iov;
 627 }
 628
 629 void iov_iter_advance(struct iov_iter *i, size_t size)
 630 {
 631         if (unlikely(i->count < size))
 632                 size = i->count;
 633         if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i))) {
 634                 i->iov_offset += size;
 635                 i->count -= size;
 636         } else if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
 637                 /* iovec and kvec have identical layouts */
 638                 iov_iter_iovec_advance(i, size);
 639         } else if (iov_iter_is_bvec(i)) {
 640                 iov_iter_bvec_advance(i, size);
 641         } else if (iov_iter_is_discard(i)) {
 642                 i->count -= size;
 643         }
 644 }
 645 EXPORT_SYMBOL(iov_iter_advance);
 646
 647 void iov_iter_revert(struct iov_iter *i, size_t unroll)
 648 {
 649         if (!unroll)
 650                 return;
 651         if (WARN_ON(unroll > MAX_RW_COUNT))
 652                 return;
 653         i->count += unroll;
 654         if (unlikely(iov_iter_is_discard(i)))
 655                 return;
 656         if (unroll <= i->iov_offset) {
 657                 i->iov_offset -= unroll;
 658                 return;
 659         }
 660         unroll -= i->iov_offset;
 661         if (iov_iter_is_xarray(i) || iter_is_ubuf(i)) {
 662                 BUG(); /* We should never go beyond the start of the specified
 663                         * range since we might then be straying into pages that
 664                         * aren't pinned.
 665                         */
 666         } else if (iov_iter_is_bvec(i)) {
 667                 const struct bio_vec *bvec = i->bvec;
 668                 while (1) {
 669                         size_t n = (--bvec)->bv_len;
 670                         i->nr_segs++;
 671                         if (unroll <= n) {
 672                                 i->bvec = bvec;
 673                                 i->iov_offset = n - unroll;
 674                                 return;
 675                         }
 676                         unroll -= n;
 677                 }
 678         } else { /* same logics for iovec and kvec */
 679                 const struct iovec *iov = iter_iov(i);
 680                 while (1) {
 681                         size_t n = (--iov)->iov_len;
 682                         i->nr_segs++;
 683                         if (unroll <= n) {
 684                                 i->__iov = iov;
 685                                 i->iov_offset = n - unroll;
 686                                 return;
 687                         }
 688                         unroll -= n;
 689                 }
 690         }
 691 }
 692 EXPORT_SYMBOL(iov_iter_revert);
 693
 694 /*
 695  * Return the count of just the current iov_iter segment.
 696  */
 697 size_t iov_iter_single_seg_count(const struct iov_iter *i)
 698 {
 699         if (i->nr_segs > 1) {
 700                 if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
 701                         return min(i->count, iter_iov(i)->iov_len - i->iov_offset);
 702                 if (iov_iter_is_bvec(i))
 703                         return min(i->count, i->bvec->bv_len - i->iov_offset);
 704         }
 705         return i->count;
 706 }
 707 EXPORT_SYMBOL(iov_iter_single_seg_count);
 708
 709 void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
 710                         const struct kvec *kvec, unsigned long nr_segs,
 711                         size_t count)
 712 {
 713         WARN_ON(direction & ~(READ | WRITE));
 714         *i = (struct iov_iter){
 715                 .iter_type = ITER_KVEC,
 716                 .copy_mc = false,
 717                 .data_source = direction,
 718                 .kvec = kvec,
 719                 .nr_segs = nr_segs,
 720                 .iov_offset = 0,
 721                 .count = count
 722         };
 723 }
 724 EXPORT_SYMBOL(iov_iter_kvec);
 725
 726 void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
 727                         const struct bio_vec *bvec, unsigned long nr_segs,
 728                         size_t count)
 729 {
 730         WARN_ON(direction & ~(READ | WRITE));
 731         *i = (struct iov_iter){
 732                 .iter_type = ITER_BVEC,
 733                 .copy_mc = false,
 734                 .data_source = direction,
 735                 .bvec = bvec,
 736                 .nr_segs = nr_segs,
 737                 .iov_offset = 0,
 738                 .count = count
 739         };
 740 }
 741 EXPORT_SYMBOL(iov_iter_bvec);
 742
 743 /**
 744  * iov_iter_xarray - Initialise an I/O iterator to use the pages in an xarray
 745  * @i: The iterator to initialise.
 746  * @direction: The direction of the transfer.
 747  * @xarray: The xarray to access.
 748  * @start: The start file position.
 749  * @count: The size of the I/O buffer in bytes.
 750  *
 751  * Set up an I/O iterator to either draw data out of the pages attached to an
 752  * inode or to inject data into those pages.  The pages *must* be prevented
 753  * from evaporation, either by taking a ref on them or locking them by the
 754  * caller.
 755  */
 756 void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
 757                      struct xarray *xarray, loff_t start, size_t count)
 758 {
 759         BUG_ON(direction & ~1);
 760         *i = (struct iov_iter) {
 761                 .iter_type = ITER_XARRAY,
 762                 .copy_mc = false,
 763                 .data_source = direction,
 764                 .xarray = xarray,
 765                 .xarray_start = start,
 766                 .count = count,
 767                 .iov_offset = 0
 768         };
 769 }
 770 EXPORT_SYMBOL(iov_iter_xarray);
 771
 772 /**
 773  * iov_iter_discard - Initialise an I/O iterator that discards data
 774  * @i: The iterator to initialise.
 775  * @direction: The direction of the transfer.
 776  * @count: The size of the I/O buffer in bytes.
 777  *
 778  * Set up an I/O iterator that just discards everything that's written to it.
 779  * It's only available as a READ iterator.
 780  */
 781 void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
 782 {
 783         BUG_ON(direction != READ);
 784         *i = (struct iov_iter){
 785                 .iter_type = ITER_DISCARD,
 786                 .copy_mc = false,
 787                 .data_source = false,
 788                 .count = count,
 789                 .iov_offset = 0
 790         };
 791 }
 792 EXPORT_SYMBOL(iov_iter_discard);
 793
 794 static bool iov_iter_aligned_iovec(const struct iov_iter *i, unsigned addr_mask,
 795                                    unsigned len_mask)
 796 {
 797         size_t size = i->count;
 798         size_t skip = i->iov_offset;
 799         unsigned k;
 800
 801         for (k = 0; k < i->nr_segs; k++, skip = 0) {
 802                 const struct iovec *iov = iter_iov(i) + k;
 803                 size_t len = iov->iov_len - skip;
 804
 805                 if (len > size)
 806                         len = size;
 807                 if (len & len_mask)
 808                         return false;
 809                 if ((unsigned long)(iov->iov_base + skip) & addr_mask)
 810                         return false;
 811
 812                 size -= len;
 813                 if (!size)
 814                         break;
 815         }
 816         return true;
 817 }
 818
 819 static bool iov_iter_aligned_bvec(const struct iov_iter *i, unsigned addr_mask,
 820                                   unsigned len_mask)
 821 {
 822         size_t size = i->count;
 823         unsigned skip = i->iov_offset;
 824         unsigned k;
 825
 826         for (k = 0; k < i->nr_segs; k++, skip = 0) {
 827                 size_t len = i->bvec[k].bv_len - skip;
 828
 829                 if (len > size)
 830                         len = size;
 831                 if (len & len_mask)
 832                         return false;
 833                 if ((unsigned long)(i->bvec[k].bv_offset + skip) & addr_mask)
 834                         return false;
 835
 836                 size -= len;
 837                 if (!size)
 838                         break;
 839         }
 840         return true;
 841 }
 842
 843 /**
 844  * iov_iter_is_aligned() - Check if the addresses and lengths of each segments
 845  *      are aligned to the parameters.
 846  *
 847  * @i: &struct iov_iter to restore
 848  * @addr_mask: bit mask to check against the iov element's addresses
 849  * @len_mask: bit mask to check against the iov element's lengths
 850  *
 851  * Return: false if any addresses or lengths intersect with the provided masks
 852  */
 853 bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
 854                          unsigned len_mask)
 855 {
 856         if (likely(iter_is_ubuf(i))) {
 857                 if (i->count & len_mask)
 858                         return false;
 859                 if ((unsigned long)(i->ubuf + i->iov_offset) & addr_mask)
 860                         return false;
 861                 return true;
 862         }
 863
 864         if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
 865                 return iov_iter_aligned_iovec(i, addr_mask, len_mask);
 866
 867         if (iov_iter_is_bvec(i))
 868                 return iov_iter_aligned_bvec(i, addr_mask, len_mask);
 869
 870         if (iov_iter_is_xarray(i)) {
 871                 if (i->count & len_mask)
 872                         return false;
 873                 if ((i->xarray_start + i->iov_offset) & addr_mask)
 874                         return false;
 875         }
 876
 877         return true;
 878 }
 879 EXPORT_SYMBOL_GPL(iov_iter_is_aligned);
 880
 881 static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
 882 {
 883         unsigned long res = 0;
 884         size_t size = i->count;
 885         size_t skip = i->iov_offset;
 886         unsigned k;
 887
 888         for (k = 0; k < i->nr_segs; k++, skip = 0) {
 889                 const struct iovec *iov = iter_iov(i) + k;
 890                 size_t len = iov->iov_len - skip;
 891                 if (len) {
 892                         res |= (unsigned long)iov->iov_base + skip;
 893                         if (len > size)
 894                                 len = size;
 895                         res |= len;
 896                         size -= len;
 897                         if (!size)
 898                                 break;
 899                 }
 900         }
 901         return res;
 902 }
 903
 904 static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)
 905 {
 906         unsigned res = 0;
 907         size_t size = i->count;
 908         unsigned skip = i->iov_offset;
 909         unsigned k;
 910
 911         for (k = 0; k < i->nr_segs; k++, skip = 0) {
 912                 size_t len = i->bvec[k].bv_len - skip;
 913                 res |= (unsigned long)i->bvec[k].bv_offset + skip;
 914                 if (len > size)
 915                         len = size;
 916                 res |= len;
 917                 size -= len;
 918                 if (!size)
 919                         break;
 920         }
 921         return res;
 922 }
 923
 924 unsigned long iov_iter_alignment(const struct iov_iter *i)
 925 {
 926         if (likely(iter_is_ubuf(i))) {
 927                 size_t size = i->count;
 928                 if (size)
 929                         return ((unsigned long)i->ubuf + i->iov_offset) | size;
 930                 return 0;
 931         }
 932
 933         /* iovec and kvec have identical layouts */
 934         if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
 935                 return iov_iter_alignment_iovec(i);
 936
 937         if (iov_iter_is_bvec(i))
 938                 return iov_iter_alignment_bvec(i);
 939
 940         if (iov_iter_is_xarray(i))
 941                 return (i->xarray_start + i->iov_offset) | i->count;
 942
 943         return 0;
 944 }
 945 EXPORT_SYMBOL(iov_iter_alignment);
 946
 947 unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
 948 {
 949         unsigned long res = 0;
 950         unsigned long v = 0;
 951         size_t size = i->count;
 952         unsigned k;
 953
 954         if (iter_is_ubuf(i))
 955                 return 0;
 956
 957         if (WARN_ON(!iter_is_iovec(i)))
 958                 return ~0U;
 959
 960         for (k = 0; k < i->nr_segs; k++) {
 961                 const struct iovec *iov = iter_iov(i) + k;
 962                 if (iov->iov_len) {
 963                         unsigned long base = (unsigned long)iov->iov_base;
 964                         if (v) // if not the first one
 965                                 res |= base | v; // this start | previous end
 966                         v = base + iov->iov_len;
 967                         if (size <= iov->iov_len)
 968                                 break;
 969                         size -= iov->iov_len;
 970                 }
 971         }
 972         return res;
 973 }
 974 EXPORT_SYMBOL(iov_iter_gap_alignment);
 975
 976 static int want_pages_array(struct page ***res, size_t size,
 977                             size_t start, unsigned int maxpages)
 978 {
 979         unsigned int count = DIV_ROUND_UP(size + start, PAGE_SIZE);
 980
 981         if (count > maxpages)
 982                 count = maxpages;
 983         WARN_ON(!count);        // caller should've prevented that
 984         if (!*res) {
 985                 *res = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
 986                 if (!*res)
 987                         return 0;
 988         }
 989         return count;
 990 }
 991
 992 static ssize_t iter_xarray_populate_pages(struct page **pages, struct xarray *xa,
 993                                           pgoff_t index, unsigned int nr_pages)
 994 {
 995         XA_STATE(xas, xa, index);
 996         struct page *page;
 997         unsigned int ret = 0;
 998
 999         rcu_read_lock();
1000         for (page = xas_load(&xas); page; page = xas_next(&xas)) {
1001                 if (xas_retry(&xas, page))
1002                         continue;
1003
1004                 /* Has the page moved or been split? */
1005                 if (unlikely(page != xas_reload(&xas))) {
1006                         xas_reset(&xas);
1007                         continue;
1008                 }
1009
1010                 pages[ret] = find_subpage(page, xas.xa_index);
1011                 get_page(pages[ret]);
1012                 if (++ret == nr_pages)
1013                         break;
1014         }
1015         rcu_read_unlock();
1016         return ret;
1017 }
1018
1019 static ssize_t iter_xarray_get_pages(struct iov_iter *i,
1020                                      struct page ***pages, size_t maxsize,
1021                                      unsigned maxpages, size_t *_start_offset)
1022 {
1023         unsigned nr, offset, count;
1024         pgoff_t index;
1025         loff_t pos;
1026
1027         pos = i->xarray_start + i->iov_offset;
1028         index = pos >> PAGE_SHIFT;
1029         offset = pos & ~PAGE_MASK;
1030         *_start_offset = offset;
1031
1032         count = want_pages_array(pages, maxsize, offset, maxpages);
1033         if (!count)
1034                 return -ENOMEM;
1035         nr = iter_xarray_populate_pages(*pages, i->xarray, index, count);
1036         if (nr == 0)
1037                 return 0;
1038
1039         maxsize = min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
1040         i->iov_offset += maxsize;
1041         i->count -= maxsize;
1042         return maxsize;
1043 }
1044
1045 /* must be done on non-empty ITER_UBUF or ITER_IOVEC one */
1046 static unsigned long first_iovec_segment(const struct iov_iter *i, size_t *size)
1047 {
1048         size_t skip;
1049         long k;
1050
1051         if (iter_is_ubuf(i))
1052                 return (unsigned long)i->ubuf + i->iov_offset;
1053
1054         for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) {
1055                 const struct iovec *iov = iter_iov(i) + k;
1056                 size_t len = iov->iov_len - skip;
1057
1058                 if (unlikely(!len))
1059                         continue;
1060                 if (*size > len)
1061                         *size = len;
1062                 return (unsigned long)iov->iov_base + skip;
1063         }
1064         BUG(); // if it had been empty, we wouldn't get called
1065 }
1066
1067 /* must be done on non-empty ITER_BVEC one */
1068 static struct page *first_bvec_segment(const struct iov_iter *i,
1069                                        size_t *size, size_t *start)
1070 {
1071         struct page *page;
1072         size_t skip = i->iov_offset, len;
1073
1074         len = i->bvec->bv_len - skip;
1075         if (*size > len)
1076                 *size = len;
1077         skip += i->bvec->bv_offset;
1078         page = i->bvec->bv_page + skip / PAGE_SIZE;
1079         *start = skip % PAGE_SIZE;
1080         return page;
1081 }
1082
1083 static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
1084                    struct page ***pages, size_t maxsize,
1085                    unsigned int maxpages, size_t *start)
1086 {
1087         unsigned int n, gup_flags = 0;
1088
1089         if (maxsize > i->count)
1090                 maxsize = i->count;
1091         if (!maxsize)
1092                 return 0;
1093         if (maxsize > MAX_RW_COUNT)
1094                 maxsize = MAX_RW_COUNT;
1095
1096         if (likely(user_backed_iter(i))) {
1097                 unsigned long addr;
1098                 int res;
1099
1100                 if (iov_iter_rw(i) != WRITE)
1101                         gup_flags |= FOLL_WRITE;
1102                 if (i->nofault)
1103                         gup_flags |= FOLL_NOFAULT;
1104
1105                 addr = first_iovec_segment(i, &maxsize);
1106                 *start = addr % PAGE_SIZE;
1107                 addr &= PAGE_MASK;
1108                 n = want_pages_array(pages, maxsize, *start, maxpages);
1109                 if (!n)
1110                         return -ENOMEM;
1111                 res = get_user_pages_fast(addr, n, gup_flags, *pages);
1112                 if (unlikely(res <= 0))
1113                         return res;
1114                 maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - *start);
1115                 iov_iter_advance(i, maxsize);
1116                 return maxsize;
1117         }
1118         if (iov_iter_is_bvec(i)) {
1119                 struct page **p;
1120                 struct page *page;
1121
1122                 page = first_bvec_segment(i, &maxsize, start);
1123                 n = want_pages_array(pages, maxsize, *start, maxpages);
1124                 if (!n)
1125                         return -ENOMEM;
1126                 p = *pages;
1127                 for (int k = 0; k < n; k++)
1128                         get_page(p[k] = page + k);
1129                 maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
1130                 i->count -= maxsize;
1131                 i->iov_offset += maxsize;
1132                 if (i->iov_offset == i->bvec->bv_len) {
1133                         i->iov_offset = 0;
1134                         i->bvec++;
1135                         i->nr_segs--;
1136                 }
1137                 return maxsize;
1138         }
1139         if (iov_iter_is_xarray(i))
1140                 return iter_xarray_get_pages(i, pages, maxsize, maxpages, start);
1141         return -EFAULT;
1142 }
1143
1144 ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
1145                 size_t maxsize, unsigned maxpages, size_t *start)
1146 {
1147         if (!maxpages)
1148                 return 0;
1149         BUG_ON(!pages);
1150
1151         return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start);
1152 }
1153 EXPORT_SYMBOL(iov_iter_get_pages2);
1154
1155 ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
1156                 struct page ***pages, size_t maxsize, size_t *start)
1157 {
1158         ssize_t len;
1159
1160         *pages = NULL;
1161
1162         len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start);
1163         if (len <= 0) {
1164                 kvfree(*pages);
1165                 *pages = NULL;
1166         }
1167         return len;
1168 }
1169 EXPORT_SYMBOL(iov_iter_get_pages_alloc2);
1170
1171 size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
1172                                struct iov_iter *i)
1173 {
1174         __wsum sum, next;
1175         sum = *csum;
1176         if (WARN_ON_ONCE(!i->data_source))
1177                 return 0;
1178
1179         iterate_and_advance(i, bytes, base, len, off, ({
1180                 next = csum_and_copy_from_user(base, addr + off, len);
1181                 sum = csum_block_add(sum, next, off);
1182                 next ? 0 : len;
1183         }), ({
1184                 sum = csum_and_memcpy(addr + off, base, len, sum, off);
1185         })
1186         )
1187         *csum = sum;
1188         return bytes;
1189 }
1190 EXPORT_SYMBOL(csum_and_copy_from_iter);
1191
1192 size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
1193                              struct iov_iter *i)
1194 {
1195         struct csum_state *csstate = _csstate;
1196         __wsum sum, next;
1197
1198         if (WARN_ON_ONCE(i->data_source))
1199                 return 0;
1200         if (unlikely(iov_iter_is_discard(i))) {
1201                 // can't use csum_memcpy() for that one - data is not copied
1202                 csstate->csum = csum_block_add(csstate->csum,
1203                                                csum_partial(addr, bytes, 0),
1204                                                csstate->off);
1205                 csstate->off += bytes;
1206                 return bytes;
1207         }
1208
1209         sum = csum_shift(csstate->csum, csstate->off);
1210         iterate_and_advance(i, bytes, base, len, off, ({
1211                 next = csum_and_copy_to_user(addr + off, base, len);
1212                 sum = csum_block_add(sum, next, off);
1213                 next ? 0 : len;
1214         }), ({
1215                 sum = csum_and_memcpy(base, addr + off, len, sum, off);
1216         })
1217         )
1218         csstate->csum = csum_shift(sum, csstate->off);
1219         csstate->off += bytes;
1220         return bytes;
1221 }
1222 EXPORT_SYMBOL(csum_and_copy_to_iter);
1223
1224 size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
1225                 struct iov_iter *i)
1226 {
1227 #ifdef CONFIG_CRYPTO_HASH
1228         struct ahash_request *hash = hashp;
1229         struct scatterlist sg;
1230         size_t copied;
1231
1232         copied = copy_to_iter(addr, bytes, i);
1233         sg_init_one(&sg, addr, copied);
1234         ahash_request_set_crypt(hash, &sg, NULL, copied);
1235         crypto_ahash_update(hash);
1236         return copied;
1237 #else
1238         return 0;
1239 #endif
1240 }
1241 EXPORT_SYMBOL(hash_and_copy_to_iter);
1242
1243 static int iov_npages(const struct iov_iter *i, int maxpages)
1244 {
1245         size_t skip = i->iov_offset, size = i->count;
1246         const struct iovec *p;
1247         int npages = 0;
1248
1249         for (p = iter_iov(i); size; skip = 0, p++) {
1250                 unsigned offs = offset_in_page(p->iov_base + skip);
1251                 size_t len = min(p->iov_len - skip, size);
1252
1253                 if (len) {
1254                         size -= len;
1255                         npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
1256                         if (unlikely(npages > maxpages))
1257                                 return maxpages;
1258                 }
1259         }
1260         return npages;
1261 }
1262
1263 static int bvec_npages(const struct iov_iter *i, int maxpages)
1264 {
1265         size_t skip = i->iov_offset, size = i->count;
1266         const struct bio_vec *p;
1267         int npages = 0;
1268
1269         for (p = i->bvec; size; skip = 0, p++) {
1270                 unsigned offs = (p->bv_offset + skip) % PAGE_SIZE;
1271                 size_t len = min(p->bv_len - skip, size);
1272
1273                 size -= len;
1274                 npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
1275                 if (unlikely(npages > maxpages))
1276                         return maxpages;
1277         }
1278         return npages;
1279 }
1280
1281 int iov_iter_npages(const struct iov_iter *i, int maxpages)
1282 {
1283         if (unlikely(!i->count))
1284                 return 0;
1285         if (likely(iter_is_ubuf(i))) {
1286                 unsigned offs = offset_in_page(i->ubuf + i->iov_offset);
1287                 int npages = DIV_ROUND_UP(offs + i->count, PAGE_SIZE);
1288                 return min(npages, maxpages);
1289         }
1290         /* iovec and kvec have identical layouts */
1291         if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
1292                 return iov_npages(i, maxpages);
1293         if (iov_iter_is_bvec(i))
1294                 return bvec_npages(i, maxpages);
1295         if (iov_iter_is_xarray(i)) {
1296                 unsigned offset = (i->xarray_start + i->iov_offset) % PAGE_SIZE;
1297                 int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
1298                 return min(npages, maxpages);
1299         }
1300         return 0;
1301 }
1302 EXPORT_SYMBOL(iov_iter_npages);
1303
1304 const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
1305 {
1306         *new = *old;
1307         if (iov_iter_is_bvec(new))
1308                 return new->bvec = kmemdup(new->bvec,
1309                                     new->nr_segs * sizeof(struct bio_vec),
1310                                     flags);
1311         else if (iov_iter_is_kvec(new) || iter_is_iovec(new))
1312                 /* iovec and kvec have identical layout */
1313                 return new->__iov = kmemdup(new->__iov,
1314                                    new->nr_segs * sizeof(struct iovec),
1315                                    flags);
1316         return NULL;
1317 }
1318 EXPORT_SYMBOL(dup_iter);
1319
1320 static __noclone int copy_compat_iovec_from_user(struct iovec *iov,
1321                 const struct iovec __user *uvec, unsigned long nr_segs)
1322 {
1323         const struct compat_iovec __user *uiov =
1324                 (const struct compat_iovec __user *)uvec;
1325         int ret = -EFAULT, i;
1326
1327         if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
1328                 return -EFAULT;
1329
1330         for (i = 0; i < nr_segs; i++) {
1331                 compat_uptr_t buf;
1332                 compat_ssize_t len;
1333
1334                 unsafe_get_user(len, &uiov[i].iov_len, uaccess_end);
1335                 unsafe_get_user(buf, &uiov[i].iov_base, uaccess_end);
1336
1337                 /* check for compat_size_t not fitting in compat_ssize_t .. */
1338                 if (len < 0) {
1339                         ret = -EINVAL;
1340                         goto uaccess_end;
1341                 }
1342                 iov[i].iov_base = compat_ptr(buf);
1343                 iov[i].iov_len = len;
1344         }
1345
1346         ret = 0;
1347 uaccess_end:
1348         user_access_end();
1349         return ret;
1350 }
1351
1352 static __noclone int copy_iovec_from_user(struct iovec *iov,
1353                 const struct iovec __user *uiov, unsigned long nr_segs)
1354 {
1355         int ret = -EFAULT;
1356
1357         if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
1358                 return -EFAULT;
1359
1360         do {
1361                 void __user *buf;
1362                 ssize_t len;
1363
1364                 unsafe_get_user(len, &uiov->iov_len, uaccess_end);
1365                 unsafe_get_user(buf, &uiov->iov_base, uaccess_end);
1366
1367                 /* check for size_t not fitting in ssize_t .. */
1368                 if (unlikely(len < 0)) {
1369                         ret = -EINVAL;
1370                         goto uaccess_end;
1371                 }
1372                 iov->iov_base = buf;
1373                 iov->iov_len = len;
1374
1375                 uiov++; iov++;
1376         } while (--nr_segs);
1377
1378         ret = 0;
1379 uaccess_end:
1380         user_access_end();
1381         return ret;
1382 }
1383
1384 struct iovec *iovec_from_user(const struct iovec __user *uvec,
1385                 unsigned long nr_segs, unsigned long fast_segs,
1386                 struct iovec *fast_iov, bool compat)
1387 {
1388         struct iovec *iov = fast_iov;
1389         int ret;
1390
1391         /*
1392          * SuS says "The readv() function *may* fail if the iovcnt argument was
1393          * less than or equal to 0, or greater than {IOV_MAX}.  Linux has
1394          * traditionally returned zero for zero segments, so...
1395          */
1396         if (nr_segs == 0)
1397                 return iov;
1398         if (nr_segs > UIO_MAXIOV)
1399                 return ERR_PTR(-EINVAL);
1400         if (nr_segs > fast_segs) {
1401                 iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
1402                 if (!iov)
1403                         return ERR_PTR(-ENOMEM);
1404         }
1405
1406         if (unlikely(compat))
1407                 ret = copy_compat_iovec_from_user(iov, uvec, nr_segs);
1408         else
1409                 ret = copy_iovec_from_user(iov, uvec, nr_segs);
1410         if (ret) {
1411                 if (iov != fast_iov)
1412                         kfree(iov);
1413                 return ERR_PTR(ret);
1414         }
1415
1416         return iov;
1417 }
1418
1419 /*
1420  * Single segment iovec supplied by the user, import it as ITER_UBUF.
1421  */
1422 static ssize_t __import_iovec_ubuf(int type, const struct iovec __user *uvec,
1423                                    struct iovec **iovp, struct iov_iter *i,
1424                                    bool compat)
1425 {
1426         struct iovec *iov = *iovp;
1427         ssize_t ret;
1428
1429         if (compat)
1430                 ret = copy_compat_iovec_from_user(iov, uvec, 1);
1431         else
1432                 ret = copy_iovec_from_user(iov, uvec, 1);
1433         if (unlikely(ret))
1434                 return ret;
1435
1436         ret = import_ubuf(type, iov->iov_base, iov->iov_len, i);
1437         if (unlikely(ret))
1438                 return ret;
1439         *iovp = NULL;
1440         return i->count;
1441 }
1442
1443 ssize_t __import_iovec(int type, const struct iovec __user *uvec,
1444                  unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
1445                  struct iov_iter *i, bool compat)
1446 {
1447         ssize_t total_len = 0;
1448         unsigned long seg;
1449         struct iovec *iov;
1450
1451         if (nr_segs == 1)
1452                 return __import_iovec_ubuf(type, uvec, iovp, i, compat);
1453
1454         iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);
1455         if (IS_ERR(iov)) {
1456                 *iovp = NULL;
1457                 return PTR_ERR(iov);
1458         }
1459
1460         /*
1461          * According to the Single Unix Specification we should return EINVAL if
1462          * an element length is < 0 when cast to ssize_t or if the total length
1463          * would overflow the ssize_t return value of the system call.
1464          *
1465          * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
1466          * overflow case.
1467          */
1468         for (seg = 0; seg < nr_segs; seg++) {
1469                 ssize_t len = (ssize_t)iov[seg].iov_len;
1470
1471                 if (!access_ok(iov[seg].iov_base, len)) {
1472                         if (iov != *iovp)
1473                                 kfree(iov);
1474                         *iovp = NULL;
1475                         return -EFAULT;
1476                 }
1477
1478                 if (len > MAX_RW_COUNT - total_len) {
1479                         len = MAX_RW_COUNT - total_len;
1480                         iov[seg].iov_len = len;
1481                 }
1482                 total_len += len;
1483         }
1484
1485         iov_iter_init(i, type, iov, nr_segs, total_len);
1486         if (iov == *iovp)
1487                 *iovp = NULL;
1488         else
1489                 *iovp = iov;
1490         return total_len;
1491 }
1492
1493 /**
1494  * import_iovec() - Copy an array of &struct iovec from userspace
1495  *     into the kernel, check that it is valid, and initialize a new
1496  *     &struct iov_iter iterator to access it.
1497  *
1498  * @type: One of %READ or %WRITE.
1499  * @uvec: Pointer to the userspace array.
1500  * @nr_segs: Number of elements in userspace array.
1501  * @fast_segs: Number of elements in @iov.
1502  * @iovp: (input and output parameter) Pointer to pointer to (usually small
1503  *     on-stack) kernel array.
1504  * @i: Pointer to iterator that will be initialized on success.
1505  *
1506  * If the array pointed to by *@iov is large enough to hold all @nr_segs,
1507  * then this function places %NULL in *@iov on return. Otherwise, a new
1508  * array will be allocated and the result placed in *@iov. This means that
1509  * the caller may call kfree() on *@iov regardless of whether the small
1510  * on-stack array was used or not (and regardless of whether this function
1511  * returns an error or not).
1512  *
1513  * Return: Negative error code on error, bytes imported on success
1514  */
1515 ssize_t import_iovec(int type, const struct iovec __user *uvec,
1516                  unsigned nr_segs, unsigned fast_segs,
1517                  struct iovec **iovp, struct iov_iter *i)
1518 {
1519         return __import_iovec(type, uvec, nr_segs, fast_segs, iovp, i,
1520                               in_compat_syscall());
1521 }
1522 EXPORT_SYMBOL(import_iovec);
1523
1524 int import_single_range(int rw, void __user *buf, size_t len,
1525                  struct iovec *iov, struct iov_iter *i)
1526 {
1527         if (len > MAX_RW_COUNT)
1528                 len = MAX_RW_COUNT;
1529         if (unlikely(!access_ok(buf, len)))
1530                 return -EFAULT;
1531
1532         iov_iter_ubuf(i, rw, buf, len);
1533         return 0;
1534 }
1535 EXPORT_SYMBOL(import_single_range);
1536
1537 int import_ubuf(int rw, void __user *buf, size_t len, struct iov_iter *i)
1538 {
1539         if (len > MAX_RW_COUNT)
1540                 len = MAX_RW_COUNT;
1541         if (unlikely(!access_ok(buf, len)))
1542                 return -EFAULT;
1543
1544         iov_iter_ubuf(i, rw, buf, len);
1545         return 0;
1546 }
1547 EXPORT_SYMBOL_GPL(import_ubuf);
1548
1549 /**
1550  * iov_iter_restore() - Restore a &struct iov_iter to the same state as when
1551  *     iov_iter_save_state() was called.
1552  *
1553  * @i: &struct iov_iter to restore
1554  * @state: state to restore from
1555  *
1556  * Used after iov_iter_save_state() to bring restore @i, if operations may
1557  * have advanced it.
1558  *
1559  * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC
1560  */
1561 void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
1562 {
1563         if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i) &&
1564                          !iter_is_ubuf(i)) && !iov_iter_is_kvec(i))
1565                 return;
1566         i->iov_offset = state->iov_offset;
1567         i->count = state->count;
1568         if (iter_is_ubuf(i))
1569                 return;
1570         /*
1571          * For the *vec iters, nr_segs + iov is constant - if we increment
1572          * the vec, then we also decrement the nr_segs count. Hence we don't
1573          * need to track both of these, just one is enough and we can deduct
1574          * the other from that. ITER_KVEC and ITER_IOVEC are the same struct
1575          * size, so we can just increment the iov pointer as they are unionzed.
1576          * ITER_BVEC _may_ be the same size on some archs, but on others it is
1577          * not. Be safe and handle it separately.
1578          */
1579         BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
1580         if (iov_iter_is_bvec(i))
1581                 i->bvec -= state->nr_segs - i->nr_segs;
1582         else
1583                 i->__iov -= state->nr_segs - i->nr_segs;
1584         i->nr_segs = state->nr_segs;
1585 }
1586
1587 /*
1588  * Extract a list of contiguous pages from an ITER_XARRAY iterator.  This does not
1589  * get references on the pages, nor does it get a pin on them.
1590  */
1591 static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i,
1592                                              struct page ***pages, size_t maxsize,
1593                                              unsigned int maxpages,
1594                                              iov_iter_extraction_t extraction_flags,
1595                                              size_t *offset0)
1596 {
1597         struct page *page, **p;
1598         unsigned int nr = 0, offset;
1599         loff_t pos = i->xarray_start + i->iov_offset;
1600         pgoff_t index = pos >> PAGE_SHIFT;
1601         XA_STATE(xas, i->xarray, index);
1602
1603         offset = pos & ~PAGE_MASK;
1604         *offset0 = offset;
1605
1606         maxpages = want_pages_array(pages, maxsize, offset, maxpages);
1607         if (!maxpages)
1608                 return -ENOMEM;
1609         p = *pages;
1610
1611         rcu_read_lock();
1612         for (page = xas_load(&xas); page; page = xas_next(&xas)) {
1613                 if (xas_retry(&xas, page))
1614                         continue;
1615
1616                 /* Has the page moved or been split? */
1617                 if (unlikely(page != xas_reload(&xas))) {
1618                         xas_reset(&xas);
1619                         continue;
1620                 }
1621
1622                 p[nr++] = find_subpage(page, xas.xa_index);
1623                 if (nr == maxpages)
1624                         break;
1625         }
1626         rcu_read_unlock();
1627
1628         maxsize = min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
1629         iov_iter_advance(i, maxsize);
1630         return maxsize;
1631 }
1632
1633 /*
1634  * Extract a list of contiguous pages from an ITER_BVEC iterator.  This does
1635  * not get references on the pages, nor does it get a pin on them.
1636  */
1637 static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
1638                                            struct page ***pages, size_t maxsize,
1639                                            unsigned int maxpages,
1640                                            iov_iter_extraction_t extraction_flags,
1641                                            size_t *offset0)
1642 {
1643         struct page **p, *page;
1644         size_t skip = i->iov_offset, offset;
1645         int k;
1646
1647         for (;;) {
1648                 if (i->nr_segs == 0)
1649                         return 0;
1650                 maxsize = min(maxsize, i->bvec->bv_len - skip);
1651                 if (maxsize)
1652                         break;
1653                 i->iov_offset = 0;
1654                 i->nr_segs--;
1655                 i->bvec++;
1656                 skip = 0;
1657         }
1658
1659         skip += i->bvec->bv_offset;
1660         page = i->bvec->bv_page + skip / PAGE_SIZE;
1661         offset = skip % PAGE_SIZE;
1662         *offset0 = offset;
1663
1664         maxpages = want_pages_array(pages, maxsize, offset, maxpages);
1665         if (!maxpages)
1666                 return -ENOMEM;
1667         p = *pages;
1668         for (k = 0; k < maxpages; k++)
1669                 p[k] = page + k;
1670
1671         maxsize = min_t(size_t, maxsize, maxpages * PAGE_SIZE - offset);
1672         iov_iter_advance(i, maxsize);
1673         return maxsize;
1674 }
1675
1676 /*
1677  * Extract a list of virtually contiguous pages from an ITER_KVEC iterator.
1678  * This does not get references on the pages, nor does it get a pin on them.
1679  */
1680 static ssize_t iov_iter_extract_kvec_pages(struct iov_iter *i,
1681                                            struct page ***pages, size_t maxsize,
1682                                            unsigned int maxpages,
1683                                            iov_iter_extraction_t extraction_flags,
1684                                            size_t *offset0)
1685 {
1686         struct page **p, *page;
1687         const void *kaddr;
1688         size_t skip = i->iov_offset, offset, len;
1689         int k;
1690
1691         for (;;) {
1692                 if (i->nr_segs == 0)
1693                         return 0;
1694                 maxsize = min(maxsize, i->kvec->iov_len - skip);
1695                 if (maxsize)
1696                         break;
1697                 i->iov_offset = 0;
1698                 i->nr_segs--;
1699                 i->kvec++;
1700                 skip = 0;
1701         }
1702
1703         kaddr = i->kvec->iov_base + skip;
1704         offset = (unsigned long)kaddr & ~PAGE_MASK;
1705         *offset0 = offset;
1706
1707         maxpages = want_pages_array(pages, maxsize, offset, maxpages);
1708         if (!maxpages)
1709                 return -ENOMEM;
1710         p = *pages;
1711
1712         kaddr -= offset;
1713         len = offset + maxsize;
1714         for (k = 0; k < maxpages; k++) {
1715                 size_t seg = min_t(size_t, len, PAGE_SIZE);
1716
1717                 if (is_vmalloc_or_module_addr(kaddr))
1718                         page = vmalloc_to_page(kaddr);
1719                 else
1720                         page = virt_to_page(kaddr);
1721
1722                 p[k] = page;
1723                 len -= seg;
1724                 kaddr += PAGE_SIZE;
1725         }
1726
1727         maxsize = min_t(size_t, maxsize, maxpages * PAGE_SIZE - offset);
1728         iov_iter_advance(i, maxsize);
1729         return maxsize;
1730 }
1731
1732 /*
1733  * Extract a list of contiguous pages from a user iterator and get a pin on
1734  * each of them.  This should only be used if the iterator is user-backed
1735  * (IOBUF/UBUF).
1736  *
1737  * It does not get refs on the pages, but the pages must be unpinned by the
1738  * caller once the transfer is complete.
1739  *
1740  * This is safe to be used where background IO/DMA *is* going to be modifying
1741  * the buffer; using a pin rather than a ref makes forces fork() to give the
1742  * child a copy of the page.
1743  */
1744 static ssize_t iov_iter_extract_user_pages(struct iov_iter *i,
1745                                            struct page ***pages,
1746                                            size_t maxsize,
1747                                            unsigned int maxpages,
1748                                            iov_iter_extraction_t extraction_flags,
1749                                            size_t *offset0)
1750 {
1751         unsigned long addr;
1752         unsigned int gup_flags = 0;
1753         size_t offset;
1754         int res;
1755
1756         if (i->data_source == ITER_DEST)
1757                 gup_flags |= FOLL_WRITE;
1758         if (extraction_flags & ITER_ALLOW_P2PDMA)
1759                 gup_flags |= FOLL_PCI_P2PDMA;
1760         if (i->nofault)
1761                 gup_flags |= FOLL_NOFAULT;
1762
1763         addr = first_iovec_segment(i, &maxsize);
1764         *offset0 = offset = addr % PAGE_SIZE;
1765         addr &= PAGE_MASK;
1766         maxpages = want_pages_array(pages, maxsize, offset, maxpages);
1767         if (!maxpages)
1768                 return -ENOMEM;
1769         res = pin_user_pages_fast(addr, maxpages, gup_flags, *pages);
1770         if (unlikely(res <= 0))
1771                 return res;
1772         maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - offset);
1773         iov_iter_advance(i, maxsize);
1774         return maxsize;
1775 }
1776
1777 /**
1778  * iov_iter_extract_pages - Extract a list of contiguous pages from an iterator
1779  * @i: The iterator to extract from
1780  * @pages: Where to return the list of pages
1781  * @maxsize: The maximum amount of iterator to extract
1782  * @maxpages: The maximum size of the list of pages
1783  * @extraction_flags: Flags to qualify request
1784  * @offset0: Where to return the starting offset into (*@pages)[0]
1785  *
1786  * Extract a list of contiguous pages from the current point of the iterator,
1787  * advancing the iterator.  The maximum number of pages and the maximum amount
1788  * of page contents can be set.
1789  *
1790  * If *@pages is NULL, a page list will be allocated to the required size and
1791  * *@pages will be set to its base.  If *@pages is not NULL, it will be assumed
1792  * that the caller allocated a page list at least @maxpages in size and this
1793  * will be filled in.
1794  *
1795  * @extraction_flags can have ITER_ALLOW_P2PDMA set to request peer-to-peer DMA
1796  * be allowed on the pages extracted.
1797  *
1798  * The iov_iter_extract_will_pin() function can be used to query how cleanup
1799  * should be performed.
1800  *
1801  * Extra refs or pins on the pages may be obtained as follows:
1802  *
1803  *  (*) If the iterator is user-backed (ITER_IOVEC/ITER_UBUF), pins will be
1804  *      added to the pages, but refs will not be taken.
1805  *      iov_iter_extract_will_pin() will return true.
1806  *
1807  *  (*) If the iterator is ITER_KVEC, ITER_BVEC or ITER_XARRAY, the pages are
1808  *      merely listed; no extra refs or pins are obtained.
1809  *      iov_iter_extract_will_pin() will return 0.
1810  *
1811  * Note also:
1812  *
1813  *  (*) Use with ITER_DISCARD is not supported as that has no content.
1814  *
1815  * On success, the function sets *@pages to the new pagelist, if allocated, and
1816  * sets *offset0 to the offset into the first page.
1817  *
1818  * It may also return -ENOMEM and -EFAULT.
1819  */
1820 ssize_t iov_iter_extract_pages(struct iov_iter *i,
1821                                struct page ***pages,
1822                                size_t maxsize,
1823                                unsigned int maxpages,
1824                                iov_iter_extraction_t extraction_flags,
1825                                size_t *offset0)
1826 {
1827         maxsize = min_t(size_t, min_t(size_t, maxsize, i->count), MAX_RW_COUNT);
1828         if (!maxsize)
1829                 return 0;
1830
1831         if (likely(user_backed_iter(i)))
1832                 return iov_iter_extract_user_pages(i, pages, maxsize,
1833                                                    maxpages, extraction_flags,
1834                                                    offset0);
1835         if (iov_iter_is_kvec(i))
1836                 return iov_iter_extract_kvec_pages(i, pages, maxsize,
1837                                                    maxpages, extraction_flags,
1838                                                    offset0);
1839         if (iov_iter_is_bvec(i))
1840                 return iov_iter_extract_bvec_pages(i, pages, maxsize,
1841                                                    maxpages, extraction_flags,
1842                                                    offset0);
1843         if (iov_iter_is_xarray(i))
1844                 return iov_iter_extract_xarray_pages(i, pages, maxsize,
1845                                                      maxpages, extraction_flags,
1846                                                      offset0);
1847         return -EFAULT;
1848 }
1849 EXPORT_SYMBOL_GPL(iov_iter_extract_pages);