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