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 #include <linux/cleancache.h>
  47
  48 #include "ext4.h"
  49
  50 #define NUM_PREALLOC_POST_READ_CTXS     128
  51
  52 static struct kmem_cache *bio_post_read_ctx_cache;
  53 static mempool_t *bio_post_read_ctx_pool;
  54
  55 /* postprocessing steps for read bios */
  56 enum bio_post_read_step {
  57         STEP_INITIAL = 0,
  58         STEP_DECRYPT,
  59         STEP_VERITY,
  60         STEP_MAX,
  61 };
  62
  63 struct bio_post_read_ctx {
  64         struct bio *bio;
  65         struct work_struct work;
  66         unsigned int cur_step;
  67         unsigned int enabled_steps;
  68 };
  69
  70 static void __read_end_io(struct bio *bio)
  71 {
  72         struct page *page;
  73         struct bio_vec *bv;
  74         struct bvec_iter_all iter_all;
  75
  76         bio_for_each_segment_all(bv, bio, iter_all) {
  77                 page = bv->bv_page;
  78
  79                 /* PG_error was set if any post_read step failed */
  80                 if (bio->bi_status || PageError(page)) {
  81                         ClearPageUptodate(page);
  82                         /* will re-read again later */
  83                         ClearPageError(page);
  84                 } else {
  85                         SetPageUptodate(page);
  86                 }
  87                 unlock_page(page);
  88         }
  89         if (bio->bi_private)
  90                 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
  91         bio_put(bio);
  92 }
  93
  94 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
  95
  96 static void decrypt_work(struct work_struct *work)
  97 {
  98         struct bio_post_read_ctx *ctx =
  99                 container_of(work, struct bio_post_read_ctx, work);
 100
 101         fscrypt_decrypt_bio(ctx->bio);
 102
 103         bio_post_read_processing(ctx);
 104 }
 105
 106 static void verity_work(struct work_struct *work)
 107 {
 108         struct bio_post_read_ctx *ctx =
 109                 container_of(work, struct bio_post_read_ctx, work);
 110         struct bio *bio = ctx->bio;
 111
 112         /*
 113          * fsverity_verify_bio() may call readpages() again, and although verity
 114          * will be disabled for that, decryption may still be needed, causing
 115          * another bio_post_read_ctx to be allocated.  So to guarantee that
 116          * mempool_alloc() never deadlocks we must free the current ctx first.
 117          * This is safe because verity is the last post-read step.
 118          */
 119         BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
 120         mempool_free(ctx, bio_post_read_ctx_pool);
 121         bio->bi_private = NULL;
 122
 123         fsverity_verify_bio(bio);
 124
 125         __read_end_io(bio);
 126 }
 127
 128 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
 129 {
 130         /*
 131          * We use different work queues for decryption and for verity because
 132          * verity may require reading metadata pages that need decryption, and
 133          * we shouldn't recurse to the same workqueue.
 134          */
 135         switch (++ctx->cur_step) {
 136         case STEP_DECRYPT:
 137                 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
 138                         INIT_WORK(&ctx->work, decrypt_work);
 139                         fscrypt_enqueue_decrypt_work(&ctx->work);
 140                         return;
 141                 }
 142                 ctx->cur_step++;
 143                 fallthrough;
 144         case STEP_VERITY:
 145                 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
 146                         INIT_WORK(&ctx->work, verity_work);
 147                         fsverity_enqueue_verify_work(&ctx->work);
 148                         return;
 149                 }
 150                 ctx->cur_step++;
 151                 fallthrough;
 152         default:
 153                 __read_end_io(ctx->bio);
 154         }
 155 }
 156
 157 static bool bio_post_read_required(struct bio *bio)
 158 {
 159         return bio->bi_private && !bio->bi_status;
 160 }
 161
 162 /*
 163  * I/O completion handler for multipage BIOs.
 164  *
 165  * The mpage code never puts partial pages into a BIO (except for end-of-file).
 166  * If a page does not map to a contiguous run of blocks then it simply falls
 167  * back to block_read_full_page().
 168  *
 169  * Why is this?  If a page's completion depends on a number of different BIOs
 170  * which can complete in any order (or at the same time) then determining the
 171  * status of that page is hard.  See end_buffer_async_read() for the details.
 172  * There is no point in duplicating all that complexity.
 173  */
 174 static void mpage_end_io(struct bio *bio)
 175 {
 176         if (bio_post_read_required(bio)) {
 177                 struct bio_post_read_ctx *ctx = bio->bi_private;
 178
 179                 ctx->cur_step = STEP_INITIAL;
 180                 bio_post_read_processing(ctx);
 181                 return;
 182         }
 183         __read_end_io(bio);
 184 }
 185
 186 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
 187 {
 188         return fsverity_active(inode) &&
 189                idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
 190 }
 191
 192 static void ext4_set_bio_post_read_ctx(struct bio *bio,
 193                                        const struct inode *inode,
 194                                        pgoff_t first_idx)
 195 {
 196         unsigned int post_read_steps = 0;
 197
 198         if (fscrypt_inode_uses_fs_layer_crypto(inode))
 199                 post_read_steps |= 1 << STEP_DECRYPT;
 200
 201         if (ext4_need_verity(inode, first_idx))
 202                 post_read_steps |= 1 << STEP_VERITY;
 203
 204         if (post_read_steps) {
 205                 /* Due to the mempool, this never fails. */
 206                 struct bio_post_read_ctx *ctx =
 207                         mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
 208
 209                 ctx->bio = bio;
 210                 ctx->enabled_steps = post_read_steps;
 211                 bio->bi_private = ctx;
 212         }
 213 }
 214
 215 static inline loff_t ext4_readpage_limit(struct inode *inode)
 216 {
 217         if (IS_ENABLED(CONFIG_FS_VERITY) &&
 218             (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
 219                 return inode->i_sb->s_maxbytes;
 220
 221         return i_size_read(inode);
 222 }
 223
 224 int ext4_mpage_readpages(struct inode *inode,
 225                 struct readahead_control *rac, struct page *page)
 226 {
 227         struct bio *bio = NULL;
 228         sector_t last_block_in_bio = 0;
 229
 230         const unsigned blkbits = inode->i_blkbits;
 231         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 232         const unsigned blocksize = 1 << blkbits;
 233         sector_t next_block;
 234         sector_t block_in_file;
 235         sector_t last_block;
 236         sector_t last_block_in_file;
 237         sector_t blocks[MAX_BUF_PER_PAGE];
 238         unsigned page_block;
 239         struct block_device *bdev = inode->i_sb->s_bdev;
 240         int length;
 241         unsigned relative_block = 0;
 242         struct ext4_map_blocks map;
 243         unsigned int nr_pages = rac ? readahead_count(rac) : 1;
 244
 245         map.m_pblk = 0;
 246         map.m_lblk = 0;
 247         map.m_len = 0;
 248         map.m_flags = 0;
 249
 250         for (; nr_pages; nr_pages--) {
 251                 int fully_mapped = 1;
 252                 unsigned first_hole = blocks_per_page;
 253
 254                 if (rac) {
 255                         page = readahead_page(rac);
 256                         prefetchw(&page->flags);
 257                 }
 258
 259                 if (page_has_buffers(page))
 260                         goto confused;
 261
 262                 block_in_file = next_block =
 263                         (sector_t)page->index << (PAGE_SHIFT - blkbits);
 264                 last_block = block_in_file + nr_pages * blocks_per_page;
 265                 last_block_in_file = (ext4_readpage_limit(inode) +
 266                                       blocksize - 1) >> blkbits;
 267                 if (last_block > last_block_in_file)
 268                         last_block = last_block_in_file;
 269                 page_block = 0;
 270
 271                 /*
 272                  * Map blocks using the previous result first.
 273                  */
 274                 if ((map.m_flags & EXT4_MAP_MAPPED) &&
 275                     block_in_file > map.m_lblk &&
 276                     block_in_file < (map.m_lblk + map.m_len)) {
 277                         unsigned map_offset = block_in_file - map.m_lblk;
 278                         unsigned last = map.m_len - map_offset;
 279
 280                         for (relative_block = 0; ; relative_block++) {
 281                                 if (relative_block == last) {
 282                                         /* needed? */
 283                                         map.m_flags &= ~EXT4_MAP_MAPPED;
 284                                         break;
 285                                 }
 286                                 if (page_block == blocks_per_page)
 287                                         break;
 288                                 blocks[page_block] = map.m_pblk + map_offset +
 289                                         relative_block;
 290                                 page_block++;
 291                                 block_in_file++;
 292                         }
 293                 }
 294
 295                 /*
 296                  * Then do more ext4_map_blocks() calls until we are
 297                  * done with this page.
 298                  */
 299                 while (page_block < blocks_per_page) {
 300                         if (block_in_file < last_block) {
 301                                 map.m_lblk = block_in_file;
 302                                 map.m_len = last_block - block_in_file;
 303
 304                                 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
 305                                 set_error_page:
 306                                         SetPageError(page);
 307                                         zero_user_segment(page, 0,
 308                                                           PAGE_SIZE);
 309                                         unlock_page(page);
 310                                         goto next_page;
 311                                 }
 312                         }
 313                         if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
 314                                 fully_mapped = 0;
 315                                 if (first_hole == blocks_per_page)
 316                                         first_hole = page_block;
 317                                 page_block++;
 318                                 block_in_file++;
 319                                 continue;
 320                         }
 321                         if (first_hole != blocks_per_page)
 322                                 goto confused;          /* hole -> non-hole */
 323
 324                         /* Contiguous blocks? */
 325                         if (page_block && blocks[page_block-1] != map.m_pblk-1)
 326                                 goto confused;
 327                         for (relative_block = 0; ; relative_block++) {
 328                                 if (relative_block == map.m_len) {
 329                                         /* needed? */
 330                                         map.m_flags &= ~EXT4_MAP_MAPPED;
 331                                         break;
 332                                 } else if (page_block == blocks_per_page)
 333                                         break;
 334                                 blocks[page_block] = map.m_pblk+relative_block;
 335                                 page_block++;
 336                                 block_in_file++;
 337                         }
 338                 }
 339                 if (first_hole != blocks_per_page) {
 340                         zero_user_segment(page, first_hole << blkbits,
 341                                           PAGE_SIZE);
 342                         if (first_hole == 0) {
 343                                 if (ext4_need_verity(inode, page->index) &&
 344                                     !fsverity_verify_page(page))
 345                                         goto set_error_page;
 346                                 SetPageUptodate(page);
 347                                 unlock_page(page);
 348                                 goto next_page;
 349                         }
 350                 } else if (fully_mapped) {
 351                         SetPageMappedToDisk(page);
 352                 }
 353                 if (fully_mapped && blocks_per_page == 1 &&
 354                     !PageUptodate(page) && cleancache_get_page(page) == 0) {
 355                         SetPageUptodate(page);
 356                         goto confused;
 357                 }
 358
 359                 /*
 360                  * This page will go to BIO.  Do we need to send this
 361                  * BIO off first?
 362                  */
 363                 if (bio && (last_block_in_bio != blocks[0] - 1 ||
 364                             !fscrypt_mergeable_bio(bio, inode, next_block))) {
 365                 submit_and_realloc:
 366                         submit_bio(bio);
 367                         bio = NULL;
 368                 }
 369                 if (bio == NULL) {
 370                         /*
 371                          * bio_alloc will _always_ be able to allocate a bio if
 372                          * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
 373                          */
 374                         bio = bio_alloc(GFP_KERNEL, bio_max_segs(nr_pages));
 375                         fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
 376                                                   GFP_KERNEL);
 377                         ext4_set_bio_post_read_ctx(bio, inode, page->index);
 378                         bio_set_dev(bio, bdev);
 379                         bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 380                         bio->bi_end_io = mpage_end_io;
 381                         bio_set_op_attrs(bio, REQ_OP_READ,
 382                                                 rac ? REQ_RAHEAD : 0);
 383                 }
 384
 385                 length = first_hole << blkbits;
 386                 if (bio_add_page(bio, page, length, 0) < length)
 387                         goto submit_and_realloc;
 388
 389                 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
 390                      (relative_block == map.m_len)) ||
 391                     (first_hole != blocks_per_page)) {
 392                         submit_bio(bio);
 393                         bio = NULL;
 394                 } else
 395                         last_block_in_bio = blocks[blocks_per_page - 1];
 396                 goto next_page;
 397         confused:
 398                 if (bio) {
 399                         submit_bio(bio);
 400                         bio = NULL;
 401                 }
 402                 if (!PageUptodate(page))
 403                         block_read_full_page(page, ext4_get_block);
 404                 else
 405                         unlock_page(page);
 406         next_page:
 407                 if (rac)
 408                         put_page(page);
 409         }
 410         if (bio)
 411                 submit_bio(bio);
 412         return 0;
 413 }
 414
 415 int __init ext4_init_post_read_processing(void)
 416 {
 417         bio_post_read_ctx_cache =
 418                 kmem_cache_create("ext4_bio_post_read_ctx",
 419                                   sizeof(struct bio_post_read_ctx), 0, 0, NULL);
 420         if (!bio_post_read_ctx_cache)
 421                 goto fail;
 422         bio_post_read_ctx_pool =
 423                 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
 424                                          bio_post_read_ctx_cache);
 425         if (!bio_post_read_ctx_pool)
 426                 goto fail_free_cache;
 427         return 0;
 428
 429 fail_free_cache:
 430         kmem_cache_destroy(bio_post_read_ctx_cache);
 431 fail:
 432         return -ENOMEM;
 433 }
 434
 435 void ext4_exit_post_read_processing(void)
 436 {
 437         mempool_destroy(bio_post_read_ctx_pool);
 438         kmem_cache_destroy(bio_post_read_ctx_cache);
 439 }