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