fs/ext4/readpage.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/fs/ext4/readpage.c
   4  *
   5  * Copyright (C) 2002, Linus Torvalds.
   6  * Copyright (C) 2015, Google, Inc.
   7  *
   8  * This was originally taken from fs/mpage.c
   9  *
  10  * The ext4_mpage_readpages() function here is intended to
  11  * replace mpage_readahead() in the general case, not just for
  12  * encrypted files.  It has some limitations (see below), where it
  13  * will fall back to read_block_full_page(), but these limitations
  14  * should only be hit when page_size != block_size.
  15  *
  16  * This will allow us to attach a callback function to support ext4
  17  * encryption.
  18  *
  19  * If anything unusual happens, such as:
  20  *
  21  * - encountering a page which has buffers
  22  * - encountering a page which has a non-hole after a hole
  23  * - encountering a page with non-contiguous blocks
  24  *
  25  * then this code just gives up and calls the buffer_head-based read function.
  26  * It does handle a page which has holes at the end - that is a common case:
  27  * the end-of-file on blocksize < PAGE_SIZE setups.
  28  *
  29  */
  30
  31 #include <linux/kernel.h>
  32 #include <linux/export.h>
  33 #include <linux/mm.h>
  34 #include <linux/kdev_t.h>
  35 #include <linux/gfp.h>
  36 #include <linux/bio.h>
  37 #include <linux/fs.h>
  38 #include <linux/buffer_head.h>
  39 #include <linux/blkdev.h>
  40 #include <linux/highmem.h>
  41 #include <linux/prefetch.h>
  42 #include <linux/mpage.h>
  43 #include <linux/writeback.h>
  44 #include <linux/backing-dev.h>
  45 #include <linux/pagevec.h>
  46
  47 #include "ext4.h"
  48
  49 #define NUM_PREALLOC_POST_READ_CTXS     128
  50
  51 static struct kmem_cache *bio_post_read_ctx_cache;
  52 static mempool_t *bio_post_read_ctx_pool;
  53
  54 /* postprocessing steps for read bios */
  55 enum bio_post_read_step {
  56         STEP_INITIAL = 0,
  57         STEP_DECRYPT,
  58         STEP_VERITY,
  59         STEP_MAX,
  60 };
  61
  62 struct bio_post_read_ctx {
  63         struct bio *bio;
  64         struct work_struct work;
  65         unsigned int cur_step;
  66         unsigned int enabled_steps;
  67 };
  68
  69 static void __read_end_io(struct bio *bio)
  70 {
  71         struct folio_iter fi;
  72
  73         bio_for_each_folio_all(fi, bio) {
  74                 struct folio *folio = fi.folio;
  75
  76                 if (bio->bi_status)
  77                         folio_clear_uptodate(folio);
  78                 else
  79                         folio_mark_uptodate(folio);
  80                 folio_unlock(folio);
  81         }
  82         if (bio->bi_private)
  83                 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
  84         bio_put(bio);
  85 }
  86
  87 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
  88
  89 static void decrypt_work(struct work_struct *work)
  90 {
  91         struct bio_post_read_ctx *ctx =
  92                 container_of(work, struct bio_post_read_ctx, work);
  93         struct bio *bio = ctx->bio;
  94
  95         if (fscrypt_decrypt_bio(bio))
  96                 bio_post_read_processing(ctx);
  97         else
  98                 __read_end_io(bio);
  99 }
 100
 101 static void verity_work(struct work_struct *work)
 102 {
 103         struct bio_post_read_ctx *ctx =
 104                 container_of(work, struct bio_post_read_ctx, work);
 105         struct bio *bio = ctx->bio;
 106
 107         /*
 108          * fsverity_verify_bio() may call readahead() again, and although verity
 109          * will be disabled for that, decryption may still be needed, causing
 110          * another bio_post_read_ctx to be allocated.  So to guarantee that
 111          * mempool_alloc() never deadlocks we must free the current ctx first.
 112          * This is safe because verity is the last post-read step.
 113          */
 114         BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
 115         mempool_free(ctx, bio_post_read_ctx_pool);
 116         bio->bi_private = NULL;
 117
 118         fsverity_verify_bio(bio);
 119
 120         __read_end_io(bio);
 121 }
 122
 123 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
 124 {
 125         /*
 126          * We use different work queues for decryption and for verity because
 127          * verity may require reading metadata pages that need decryption, and
 128          * we shouldn't recurse to the same workqueue.
 129          */
 130         switch (++ctx->cur_step) {
 131         case STEP_DECRYPT:
 132                 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
 133                         INIT_WORK(&ctx->work, decrypt_work);
 134                         fscrypt_enqueue_decrypt_work(&ctx->work);
 135                         return;
 136                 }
 137                 ctx->cur_step++;
 138                 fallthrough;
 139         case STEP_VERITY:
 140                 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
 141                         INIT_WORK(&ctx->work, verity_work);
 142                         fsverity_enqueue_verify_work(&ctx->work);
 143                         return;
 144                 }
 145                 ctx->cur_step++;
 146                 fallthrough;
 147         default:
 148                 __read_end_io(ctx->bio);
 149         }
 150 }
 151
 152 static bool bio_post_read_required(struct bio *bio)
 153 {
 154         return bio->bi_private && !bio->bi_status;
 155 }
 156
 157 /*
 158  * I/O completion handler for multipage BIOs.
 159  *
 160  * The mpage code never puts partial pages into a BIO (except for end-of-file).
 161  * If a page does not map to a contiguous run of blocks then it simply falls
 162  * back to block_read_full_folio().
 163  *
 164  * Why is this?  If a page's completion depends on a number of different BIOs
 165  * which can complete in any order (or at the same time) then determining the
 166  * status of that page is hard.  See end_buffer_async_read() for the details.
 167  * There is no point in duplicating all that complexity.
 168  */
 169 static void mpage_end_io(struct bio *bio)
 170 {
 171         if (bio_post_read_required(bio)) {
 172                 struct bio_post_read_ctx *ctx = bio->bi_private;
 173
 174                 ctx->cur_step = STEP_INITIAL;
 175                 bio_post_read_processing(ctx);
 176                 return;
 177         }
 178         __read_end_io(bio);
 179 }
 180
 181 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
 182 {
 183         return fsverity_active(inode) &&
 184                idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
 185 }
 186
 187 static void ext4_set_bio_post_read_ctx(struct bio *bio,
 188                                        const struct inode *inode,
 189                                        pgoff_t first_idx)
 190 {
 191         unsigned int post_read_steps = 0;
 192
 193         if (fscrypt_inode_uses_fs_layer_crypto(inode))
 194                 post_read_steps |= 1 << STEP_DECRYPT;
 195
 196         if (ext4_need_verity(inode, first_idx))
 197                 post_read_steps |= 1 << STEP_VERITY;
 198
 199         if (post_read_steps) {
 200                 /* Due to the mempool, this never fails. */
 201                 struct bio_post_read_ctx *ctx =
 202                         mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
 203
 204                 ctx->bio = bio;
 205                 ctx->enabled_steps = post_read_steps;
 206                 bio->bi_private = ctx;
 207         }
 208 }
 209
 210 static inline loff_t ext4_readpage_limit(struct inode *inode)
 211 {
 212         if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
 213                 return inode->i_sb->s_maxbytes;
 214
 215         return i_size_read(inode);
 216 }
 217
 218 int ext4_mpage_readpages(struct inode *inode,
 219                 struct readahead_control *rac, struct folio *folio)
 220 {
 221         struct bio *bio = NULL;
 222         sector_t last_block_in_bio = 0;
 223
 224         const unsigned blkbits = inode->i_blkbits;
 225         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 226         const unsigned blocksize = 1 << blkbits;
 227         sector_t next_block;
 228         sector_t block_in_file;
 229         sector_t last_block;
 230         sector_t last_block_in_file;
 231         sector_t blocks[MAX_BUF_PER_PAGE];
 232         unsigned page_block;
 233         struct block_device *bdev = inode->i_sb->s_bdev;
 234         int length;
 235         unsigned relative_block = 0;
 236         struct ext4_map_blocks map;
 237         unsigned int nr_pages = rac ? readahead_count(rac) : 1;
 238
 239         map.m_pblk = 0;
 240         map.m_lblk = 0;
 241         map.m_len = 0;
 242         map.m_flags = 0;
 243
 244         for (; nr_pages; nr_pages--) {
 245                 int fully_mapped = 1;
 246                 unsigned first_hole = blocks_per_page;
 247
 248                 if (rac)
 249                         folio = readahead_folio(rac);
 250                 prefetchw(&folio->flags);
 251
 252                 if (folio_buffers(folio))
 253                         goto confused;
 254
 255                 block_in_file = next_block =
 256                         (sector_t)folio->index << (PAGE_SHIFT - blkbits);
 257                 last_block = block_in_file + nr_pages * blocks_per_page;
 258                 last_block_in_file = (ext4_readpage_limit(inode) +
 259                                       blocksize - 1) >> blkbits;
 260                 if (last_block > last_block_in_file)
 261                         last_block = last_block_in_file;
 262                 page_block = 0;
 263
 264                 /*
 265                  * Map blocks using the previous result first.
 266                  */
 267                 if ((map.m_flags & EXT4_MAP_MAPPED) &&
 268                     block_in_file > map.m_lblk &&
 269                     block_in_file < (map.m_lblk + map.m_len)) {
 270                         unsigned map_offset = block_in_file - map.m_lblk;
 271                         unsigned last = map.m_len - map_offset;
 272
 273                         for (relative_block = 0; ; relative_block++) {
 274                                 if (relative_block == last) {
 275                                         /* needed? */
 276                                         map.m_flags &= ~EXT4_MAP_MAPPED;
 277                                         break;
 278                                 }
 279                                 if (page_block == blocks_per_page)
 280                                         break;
 281                                 blocks[page_block] = map.m_pblk + map_offset +
 282                                         relative_block;
 283                                 page_block++;
 284                                 block_in_file++;
 285                         }
 286                 }
 287
 288                 /*
 289                  * Then do more ext4_map_blocks() calls until we are
 290                  * done with this folio.
 291                  */
 292                 while (page_block < blocks_per_page) {
 293                         if (block_in_file < last_block) {
 294                                 map.m_lblk = block_in_file;
 295                                 map.m_len = last_block - block_in_file;
 296
 297                                 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
 298                                 set_error_page:
 299                                         folio_set_error(folio);
 300                                         folio_zero_segment(folio, 0,
 301                                                           folio_size(folio));
 302                                         folio_unlock(folio);
 303                                         goto next_page;
 304                                 }
 305                         }
 306                         if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
 307                                 fully_mapped = 0;
 308                                 if (first_hole == blocks_per_page)
 309                                         first_hole = page_block;
 310                                 page_block++;
 311                                 block_in_file++;
 312                                 continue;
 313                         }
 314                         if (first_hole != blocks_per_page)
 315                                 goto confused;          /* hole -> non-hole */
 316
 317                         /* Contiguous blocks? */
 318                         if (page_block && blocks[page_block-1] != map.m_pblk-1)
 319                                 goto confused;
 320                         for (relative_block = 0; ; relative_block++) {
 321                                 if (relative_block == map.m_len) {
 322                                         /* needed? */
 323                                         map.m_flags &= ~EXT4_MAP_MAPPED;
 324                                         break;
 325                                 } else if (page_block == blocks_per_page)
 326                                         break;
 327                                 blocks[page_block] = map.m_pblk+relative_block;
 328                                 page_block++;
 329                                 block_in_file++;
 330                         }
 331                 }
 332                 if (first_hole != blocks_per_page) {
 333                         folio_zero_segment(folio, first_hole << blkbits,
 334                                           folio_size(folio));
 335                         if (first_hole == 0) {
 336                                 if (ext4_need_verity(inode, folio->index) &&
 337                                     !fsverity_verify_folio(folio))
 338                                         goto set_error_page;
 339                                 folio_mark_uptodate(folio);
 340                                 folio_unlock(folio);
 341                                 continue;
 342                         }
 343                 } else if (fully_mapped) {
 344                         folio_set_mappedtodisk(folio);
 345                 }
 346
 347                 /*
 348                  * This folio will go to BIO.  Do we need to send this
 349                  * BIO off first?
 350                  */
 351                 if (bio && (last_block_in_bio != blocks[0] - 1 ||
 352                             !fscrypt_mergeable_bio(bio, inode, next_block))) {
 353                 submit_and_realloc:
 354                         submit_bio(bio);
 355                         bio = NULL;
 356                 }
 357                 if (bio == NULL) {
 358                         /*
 359                          * bio_alloc will _always_ be able to allocate a bio if
 360                          * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
 361                          */
 362                         bio = bio_alloc(bdev, bio_max_segs(nr_pages),
 363                                         REQ_OP_READ, GFP_KERNEL);
 364                         fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
 365                                                   GFP_KERNEL);
 366                         ext4_set_bio_post_read_ctx(bio, inode, folio->index);
 367                         bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 368                         bio->bi_end_io = mpage_end_io;
 369                         if (rac)
 370                                 bio->bi_opf |= REQ_RAHEAD;
 371                 }
 372
 373                 length = first_hole << blkbits;
 374                 if (!bio_add_folio(bio, folio, length, 0))
 375                         goto submit_and_realloc;
 376
 377                 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
 378                      (relative_block == map.m_len)) ||
 379                     (first_hole != blocks_per_page)) {
 380                         submit_bio(bio);
 381                         bio = NULL;
 382                 } else
 383                         last_block_in_bio = blocks[blocks_per_page - 1];
 384                 continue;
 385         confused:
 386                 if (bio) {
 387                         submit_bio(bio);
 388                         bio = NULL;
 389                 }
 390                 if (!folio_test_uptodate(folio))
 391                         block_read_full_folio(folio, ext4_get_block);
 392                 else
 393                         folio_unlock(folio);
 394 next_page:
 395                 ; /* A label shall be followed by a statement until C23 */
 396         }
 397         if (bio)
 398                 submit_bio(bio);
 399         return 0;
 400 }
 401
 402 int __init ext4_init_post_read_processing(void)
 403 {
 404         bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);
 405
 406         if (!bio_post_read_ctx_cache)
 407                 goto fail;
 408         bio_post_read_ctx_pool =
 409                 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
 410                                          bio_post_read_ctx_cache);
 411         if (!bio_post_read_ctx_pool)
 412                 goto fail_free_cache;
 413         return 0;
 414
 415 fail_free_cache:
 416         kmem_cache_destroy(bio_post_read_ctx_cache);
 417 fail:
 418         return -ENOMEM;
 419 }
 420
 421 void ext4_exit_post_read_processing(void)
 422 {
 423         mempool_destroy(bio_post_read_ctx_pool);
 424         kmem_cache_destroy(bio_post_read_ctx_cache);
 425 }