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/blk-crypto.h> 40 #include <linux/blkdev.h> 41 #include <linux/highmem.h> 42 #include <linux/prefetch.h> 43 #include <linux/mpage.h> 44 #include <linux/writeback.h> 45 #include <linux/backing-dev.h> 46 47 #include "ext4.h" 48 #include <trace/events/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 fsverity_info *vi; 66 struct work_struct work; 67 unsigned int cur_step; 68 unsigned int enabled_steps; 69 }; 70 71 static void __read_end_io(struct bio *bio) 72 { 73 struct folio_iter fi; 74 75 bio_for_each_folio_all(fi, bio) 76 folio_end_read(fi.folio, bio->bi_status == 0); 77 if (bio->bi_private) 78 mempool_free(bio->bi_private, bio_post_read_ctx_pool); 79 bio_put(bio); 80 } 81 82 static void bio_post_read_processing(struct bio_post_read_ctx *ctx); 83 84 static void decrypt_work(struct work_struct *work) 85 { 86 struct bio_post_read_ctx *ctx = 87 container_of(work, struct bio_post_read_ctx, work); 88 struct bio *bio = ctx->bio; 89 90 if (fscrypt_decrypt_bio(bio)) 91 bio_post_read_processing(ctx); 92 else 93 __read_end_io(bio); 94 } 95 96 static void verity_work(struct work_struct *work) 97 { 98 struct bio_post_read_ctx *ctx = 99 container_of(work, struct bio_post_read_ctx, work); 100 struct bio *bio = ctx->bio; 101 struct fsverity_info *vi = ctx->vi; 102 103 /* 104 * fsverity_verify_bio() may call readahead() again, and although verity 105 * will be disabled for that, decryption may still be needed, causing 106 * another bio_post_read_ctx to be allocated. So to guarantee that 107 * mempool_alloc() never deadlocks we must free the current ctx first. 108 * This is safe because verity is the last post-read step. 109 */ 110 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX); 111 mempool_free(ctx, bio_post_read_ctx_pool); 112 bio->bi_private = NULL; 113 114 fsverity_verify_bio(vi, bio); 115 116 __read_end_io(bio); 117 } 118 119 static void bio_post_read_processing(struct bio_post_read_ctx *ctx) 120 { 121 /* 122 * We use different work queues for decryption and for verity because 123 * verity may require reading metadata pages that need decryption, and 124 * we shouldn't recurse to the same workqueue. 125 */ 126 switch (++ctx->cur_step) { 127 case STEP_DECRYPT: 128 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) { 129 INIT_WORK(&ctx->work, decrypt_work); 130 fscrypt_enqueue_decrypt_work(&ctx->work); 131 return; 132 } 133 ctx->cur_step++; 134 fallthrough; 135 case STEP_VERITY: 136 if (IS_ENABLED(CONFIG_FS_VERITY) && 137 ctx->enabled_steps & (1 << STEP_VERITY)) { 138 INIT_WORK(&ctx->work, verity_work); 139 fsverity_enqueue_verify_work(&ctx->work); 140 return; 141 } 142 ctx->cur_step++; 143 fallthrough; 144 default: 145 __read_end_io(ctx->bio); 146 } 147 } 148 149 static bool bio_post_read_required(struct bio *bio) 150 { 151 return bio->bi_private && !bio->bi_status; 152 } 153 154 /* 155 * I/O completion handler for multipage BIOs. 156 * 157 * The mpage code never puts partial pages into a BIO (except for end-of-file). 158 * If a page does not map to a contiguous run of blocks then it simply falls 159 * back to block_read_full_folio(). 160 * 161 * Why is this? If a page's completion depends on a number of different BIOs 162 * which can complete in any order (or at the same time) then determining the 163 * status of that page is hard. See end_buffer_async_read() for the details. 164 * There is no point in duplicating all that complexity. 165 */ 166 static void mpage_end_io(struct bio *bio) 167 { 168 if (bio_post_read_required(bio)) { 169 struct bio_post_read_ctx *ctx = bio->bi_private; 170 171 ctx->cur_step = STEP_INITIAL; 172 bio_post_read_processing(ctx); 173 return; 174 } 175 __read_end_io(bio); 176 } 177 178 static void ext4_set_bio_post_read_ctx(struct bio *bio, 179 const struct inode *inode, 180 struct fsverity_info *vi) 181 { 182 unsigned int post_read_steps = 0; 183 184 if (fscrypt_inode_uses_fs_layer_crypto(inode)) 185 post_read_steps |= 1 << STEP_DECRYPT; 186 187 if (vi) 188 post_read_steps |= 1 << STEP_VERITY; 189 190 if (post_read_steps) { 191 /* Due to the mempool, this never fails. */ 192 struct bio_post_read_ctx *ctx = 193 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS); 194 195 ctx->bio = bio; 196 ctx->vi = vi; 197 ctx->enabled_steps = post_read_steps; 198 bio->bi_private = ctx; 199 } 200 } 201 202 static inline loff_t ext4_readpage_limit(struct inode *inode) 203 { 204 if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode)) 205 return inode->i_sb->s_maxbytes; 206 207 return i_size_read(inode); 208 } 209 210 static int ext4_mpage_readpages(struct inode *inode, struct fsverity_info *vi, 211 struct readahead_control *rac, struct folio *folio) 212 { 213 struct bio *bio = NULL; 214 sector_t last_block_in_bio = 0; 215 const unsigned blkbits = inode->i_blkbits; 216 const unsigned blocksize = 1 << blkbits; 217 sector_t next_block; 218 sector_t block_in_file; 219 sector_t last_block; 220 sector_t last_block_in_file; 221 sector_t first_block; 222 unsigned page_block; 223 struct block_device *bdev = inode->i_sb->s_bdev; 224 int length; 225 unsigned relative_block = 0; 226 struct ext4_map_blocks map; 227 unsigned int nr_pages, folio_pages; 228 229 map.m_pblk = 0; 230 map.m_lblk = 0; 231 map.m_len = 0; 232 map.m_flags = 0; 233 234 nr_pages = rac ? readahead_count(rac) : folio_nr_pages(folio); 235 for (; nr_pages; nr_pages -= folio_pages) { 236 int fully_mapped = 1; 237 unsigned int first_hole; 238 unsigned int blocks_per_folio; 239 240 if (rac) 241 folio = readahead_folio(rac); 242 243 folio_pages = folio_nr_pages(folio); 244 prefetchw(&folio->flags); 245 246 if (folio_buffers(folio)) 247 goto confused; 248 249 blocks_per_folio = folio_size(folio) >> blkbits; 250 first_hole = blocks_per_folio; 251 block_in_file = next_block = EXT4_PG_TO_LBLK(inode, folio->index); 252 last_block = EXT4_PG_TO_LBLK(inode, folio->index + nr_pages); 253 last_block_in_file = (ext4_readpage_limit(inode) + 254 blocksize - 1) >> blkbits; 255 if (last_block > last_block_in_file) 256 last_block = last_block_in_file; 257 page_block = 0; 258 259 /* 260 * Map blocks using the previous result first. 261 */ 262 if ((map.m_flags & EXT4_MAP_MAPPED) && 263 block_in_file > map.m_lblk && 264 block_in_file < (map.m_lblk + map.m_len)) { 265 unsigned map_offset = block_in_file - map.m_lblk; 266 unsigned last = map.m_len - map_offset; 267 268 first_block = map.m_pblk + map_offset; 269 for (relative_block = 0; ; relative_block++) { 270 if (relative_block == last) { 271 /* needed? */ 272 map.m_flags &= ~EXT4_MAP_MAPPED; 273 break; 274 } 275 if (page_block == blocks_per_folio) 276 break; 277 page_block++; 278 block_in_file++; 279 } 280 } 281 282 /* 283 * Then do more ext4_map_blocks() calls until we are 284 * done with this folio. 285 */ 286 while (page_block < blocks_per_folio) { 287 if (block_in_file < last_block) { 288 map.m_lblk = block_in_file; 289 map.m_len = last_block - block_in_file; 290 291 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { 292 set_error_page: 293 folio_zero_segment(folio, 0, 294 folio_size(folio)); 295 folio_unlock(folio); 296 goto next_page; 297 } 298 } 299 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { 300 fully_mapped = 0; 301 if (first_hole == blocks_per_folio) 302 first_hole = page_block; 303 page_block++; 304 block_in_file++; 305 continue; 306 } 307 if (first_hole != blocks_per_folio) 308 goto confused; /* hole -> non-hole */ 309 310 /* Contiguous blocks? */ 311 if (!page_block) 312 first_block = map.m_pblk; 313 else if (first_block + page_block != map.m_pblk) 314 goto confused; 315 for (relative_block = 0; ; relative_block++) { 316 if (relative_block == map.m_len) { 317 /* needed? */ 318 map.m_flags &= ~EXT4_MAP_MAPPED; 319 break; 320 } else if (page_block == blocks_per_folio) 321 break; 322 page_block++; 323 block_in_file++; 324 } 325 } 326 if (first_hole != blocks_per_folio) { 327 folio_zero_segment(folio, first_hole << blkbits, 328 folio_size(folio)); 329 if (first_hole == 0) { 330 if (vi && !fsverity_verify_folio(vi, folio)) 331 goto set_error_page; 332 folio_end_read(folio, true); 333 continue; 334 } 335 } else if (fully_mapped) { 336 folio_set_mappedtodisk(folio); 337 } 338 339 /* 340 * This folio will go to BIO. Do we need to send this 341 * BIO off first? 342 */ 343 if (bio && (last_block_in_bio != first_block - 1 || 344 !fscrypt_mergeable_bio(bio, inode, next_block))) { 345 submit_and_realloc: 346 blk_crypto_submit_bio(bio); 347 bio = NULL; 348 } 349 if (bio == NULL) { 350 /* 351 * bio_alloc will _always_ be able to allocate a bio if 352 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 353 */ 354 bio = bio_alloc(bdev, bio_max_segs(nr_pages), 355 REQ_OP_READ, GFP_KERNEL); 356 fscrypt_set_bio_crypt_ctx(bio, inode, next_block, 357 GFP_KERNEL); 358 ext4_set_bio_post_read_ctx(bio, inode, vi); 359 bio->bi_iter.bi_sector = first_block << (blkbits - 9); 360 bio->bi_end_io = mpage_end_io; 361 if (rac) 362 bio->bi_opf |= REQ_RAHEAD; 363 } 364 365 length = first_hole << blkbits; 366 if (!bio_add_folio(bio, folio, length, 0)) 367 goto submit_and_realloc; 368 369 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 370 (relative_block == map.m_len)) || 371 (first_hole != blocks_per_folio)) { 372 blk_crypto_submit_bio(bio); 373 bio = NULL; 374 } else 375 last_block_in_bio = first_block + blocks_per_folio - 1; 376 continue; 377 confused: 378 if (bio) { 379 blk_crypto_submit_bio(bio); 380 bio = NULL; 381 } 382 if (!folio_test_uptodate(folio)) 383 block_read_full_folio(folio, ext4_get_block); 384 else 385 folio_unlock(folio); 386 next_page: 387 ; /* A label shall be followed by a statement until C23 */ 388 } 389 if (bio) 390 blk_crypto_submit_bio(bio); 391 return 0; 392 } 393 394 int ext4_read_folio(struct file *file, struct folio *folio) 395 { 396 struct inode *inode = folio->mapping->host; 397 struct fsverity_info *vi = NULL; 398 int ret; 399 400 trace_ext4_read_folio(inode, folio); 401 402 if (ext4_has_inline_data(inode)) { 403 ret = ext4_readpage_inline(inode, folio); 404 if (ret != -EAGAIN) 405 return ret; 406 } 407 408 if (folio->index < DIV_ROUND_UP(inode->i_size, PAGE_SIZE)) 409 vi = fsverity_get_info(inode); 410 if (vi) 411 fsverity_readahead(vi, folio->index, folio_nr_pages(folio)); 412 return ext4_mpage_readpages(inode, vi, NULL, folio); 413 } 414 415 void ext4_readahead(struct readahead_control *rac) 416 { 417 struct inode *inode = rac->mapping->host; 418 struct fsverity_info *vi = NULL; 419 420 /* If the file has inline data, no need to do readahead. */ 421 if (ext4_has_inline_data(inode)) 422 return; 423 424 if (readahead_index(rac) < DIV_ROUND_UP(inode->i_size, PAGE_SIZE)) 425 vi = fsverity_get_info(inode); 426 if (vi) 427 fsverity_readahead(vi, readahead_index(rac), 428 readahead_count(rac)); 429 ext4_mpage_readpages(inode, vi, rac, NULL); 430 } 431 432 int __init ext4_init_post_read_processing(void) 433 { 434 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT); 435 436 if (!bio_post_read_ctx_cache) 437 goto fail; 438 bio_post_read_ctx_pool = 439 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 440 bio_post_read_ctx_cache); 441 if (!bio_post_read_ctx_pool) 442 goto fail_free_cache; 443 return 0; 444 445 fail_free_cache: 446 kmem_cache_destroy(bio_post_read_ctx_cache); 447 fail: 448 return -ENOMEM; 449 } 450 451 void ext4_exit_post_read_processing(void) 452 { 453 mempool_destroy(bio_post_read_ctx_pool); 454 kmem_cache_destroy(bio_post_read_ctx_cache); 455 } 456