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_zero_segment(folio, 0, 300 folio_size(folio)); 301 folio_unlock(folio); 302 goto next_page; 303 } 304 } 305 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { 306 fully_mapped = 0; 307 if (first_hole == blocks_per_page) 308 first_hole = page_block; 309 page_block++; 310 block_in_file++; 311 continue; 312 } 313 if (first_hole != blocks_per_page) 314 goto confused; /* hole -> non-hole */ 315 316 /* Contiguous blocks? */ 317 if (page_block && blocks[page_block-1] != map.m_pblk-1) 318 goto confused; 319 for (relative_block = 0; ; relative_block++) { 320 if (relative_block == map.m_len) { 321 /* needed? */ 322 map.m_flags &= ~EXT4_MAP_MAPPED; 323 break; 324 } else if (page_block == blocks_per_page) 325 break; 326 blocks[page_block] = map.m_pblk+relative_block; 327 page_block++; 328 block_in_file++; 329 } 330 } 331 if (first_hole != blocks_per_page) { 332 folio_zero_segment(folio, first_hole << blkbits, 333 folio_size(folio)); 334 if (first_hole == 0) { 335 if (ext4_need_verity(inode, folio->index) && 336 !fsverity_verify_folio(folio)) 337 goto set_error_page; 338 folio_mark_uptodate(folio); 339 folio_unlock(folio); 340 continue; 341 } 342 } else if (fully_mapped) { 343 folio_set_mappedtodisk(folio); 344 } 345 346 /* 347 * This folio will go to BIO. Do we need to send this 348 * BIO off first? 349 */ 350 if (bio && (last_block_in_bio != blocks[0] - 1 || 351 !fscrypt_mergeable_bio(bio, inode, next_block))) { 352 submit_and_realloc: 353 submit_bio(bio); 354 bio = NULL; 355 } 356 if (bio == NULL) { 357 /* 358 * bio_alloc will _always_ be able to allocate a bio if 359 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 360 */ 361 bio = bio_alloc(bdev, bio_max_segs(nr_pages), 362 REQ_OP_READ, GFP_KERNEL); 363 fscrypt_set_bio_crypt_ctx(bio, inode, next_block, 364 GFP_KERNEL); 365 ext4_set_bio_post_read_ctx(bio, inode, folio->index); 366 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); 367 bio->bi_end_io = mpage_end_io; 368 if (rac) 369 bio->bi_opf |= REQ_RAHEAD; 370 } 371 372 length = first_hole << blkbits; 373 if (!bio_add_folio(bio, folio, length, 0)) 374 goto submit_and_realloc; 375 376 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 377 (relative_block == map.m_len)) || 378 (first_hole != blocks_per_page)) { 379 submit_bio(bio); 380 bio = NULL; 381 } else 382 last_block_in_bio = blocks[blocks_per_page - 1]; 383 continue; 384 confused: 385 if (bio) { 386 submit_bio(bio); 387 bio = NULL; 388 } 389 if (!folio_test_uptodate(folio)) 390 block_read_full_folio(folio, ext4_get_block); 391 else 392 folio_unlock(folio); 393 next_page: 394 ; /* A label shall be followed by a statement until C23 */ 395 } 396 if (bio) 397 submit_bio(bio); 398 return 0; 399 } 400 401 int __init ext4_init_post_read_processing(void) 402 { 403 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT); 404 405 if (!bio_post_read_ctx_cache) 406 goto fail; 407 bio_post_read_ctx_pool = 408 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 409 bio_post_read_ctx_cache); 410 if (!bio_post_read_ctx_pool) 411 goto fail_free_cache; 412 return 0; 413 414 fail_free_cache: 415 kmem_cache_destroy(bio_post_read_ctx_cache); 416 fail: 417 return -ENOMEM; 418 } 419 420 void ext4_exit_post_read_processing(void) 421 { 422 mempool_destroy(bio_post_read_ctx_pool); 423 kmem_cache_destroy(bio_post_read_ctx_cache); 424 } 425