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 folio_end_read(fi.folio, bio->bi_status == 0); 75 if (bio->bi_private) 76 mempool_free(bio->bi_private, bio_post_read_ctx_pool); 77 bio_put(bio); 78 } 79 80 static void bio_post_read_processing(struct bio_post_read_ctx *ctx); 81 82 static void decrypt_work(struct work_struct *work) 83 { 84 struct bio_post_read_ctx *ctx = 85 container_of(work, struct bio_post_read_ctx, work); 86 struct bio *bio = ctx->bio; 87 88 if (fscrypt_decrypt_bio(bio)) 89 bio_post_read_processing(ctx); 90 else 91 __read_end_io(bio); 92 } 93 94 static void verity_work(struct work_struct *work) 95 { 96 struct bio_post_read_ctx *ctx = 97 container_of(work, struct bio_post_read_ctx, work); 98 struct bio *bio = ctx->bio; 99 100 /* 101 * fsverity_verify_bio() may call readahead() again, and although verity 102 * will be disabled for that, decryption may still be needed, causing 103 * another bio_post_read_ctx to be allocated. So to guarantee that 104 * mempool_alloc() never deadlocks we must free the current ctx first. 105 * This is safe because verity is the last post-read step. 106 */ 107 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX); 108 mempool_free(ctx, bio_post_read_ctx_pool); 109 bio->bi_private = NULL; 110 111 fsverity_verify_bio(bio); 112 113 __read_end_io(bio); 114 } 115 116 static void bio_post_read_processing(struct bio_post_read_ctx *ctx) 117 { 118 /* 119 * We use different work queues for decryption and for verity because 120 * verity may require reading metadata pages that need decryption, and 121 * we shouldn't recurse to the same workqueue. 122 */ 123 switch (++ctx->cur_step) { 124 case STEP_DECRYPT: 125 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) { 126 INIT_WORK(&ctx->work, decrypt_work); 127 fscrypt_enqueue_decrypt_work(&ctx->work); 128 return; 129 } 130 ctx->cur_step++; 131 fallthrough; 132 case STEP_VERITY: 133 if (ctx->enabled_steps & (1 << STEP_VERITY)) { 134 INIT_WORK(&ctx->work, verity_work); 135 fsverity_enqueue_verify_work(&ctx->work); 136 return; 137 } 138 ctx->cur_step++; 139 fallthrough; 140 default: 141 __read_end_io(ctx->bio); 142 } 143 } 144 145 static bool bio_post_read_required(struct bio *bio) 146 { 147 return bio->bi_private && !bio->bi_status; 148 } 149 150 /* 151 * I/O completion handler for multipage BIOs. 152 * 153 * The mpage code never puts partial pages into a BIO (except for end-of-file). 154 * If a page does not map to a contiguous run of blocks then it simply falls 155 * back to block_read_full_folio(). 156 * 157 * Why is this? If a page's completion depends on a number of different BIOs 158 * which can complete in any order (or at the same time) then determining the 159 * status of that page is hard. See end_buffer_async_read() for the details. 160 * There is no point in duplicating all that complexity. 161 */ 162 static void mpage_end_io(struct bio *bio) 163 { 164 if (bio_post_read_required(bio)) { 165 struct bio_post_read_ctx *ctx = bio->bi_private; 166 167 ctx->cur_step = STEP_INITIAL; 168 bio_post_read_processing(ctx); 169 return; 170 } 171 __read_end_io(bio); 172 } 173 174 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx) 175 { 176 return fsverity_active(inode) && 177 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE); 178 } 179 180 static void ext4_set_bio_post_read_ctx(struct bio *bio, 181 const struct inode *inode, 182 pgoff_t first_idx) 183 { 184 unsigned int post_read_steps = 0; 185 186 if (fscrypt_inode_uses_fs_layer_crypto(inode)) 187 post_read_steps |= 1 << STEP_DECRYPT; 188 189 if (ext4_need_verity(inode, first_idx)) 190 post_read_steps |= 1 << STEP_VERITY; 191 192 if (post_read_steps) { 193 /* Due to the mempool, this never fails. */ 194 struct bio_post_read_ctx *ctx = 195 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS); 196 197 ctx->bio = bio; 198 ctx->enabled_steps = post_read_steps; 199 bio->bi_private = ctx; 200 } 201 } 202 203 static inline loff_t ext4_readpage_limit(struct inode *inode) 204 { 205 if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode)) 206 return inode->i_sb->s_maxbytes; 207 208 return i_size_read(inode); 209 } 210 211 int ext4_mpage_readpages(struct inode *inode, 212 struct readahead_control *rac, struct folio *folio) 213 { 214 struct bio *bio = NULL; 215 sector_t last_block_in_bio = 0; 216 217 const unsigned blkbits = inode->i_blkbits; 218 const unsigned blocks_per_page = PAGE_SIZE >> blkbits; 219 const unsigned blocksize = 1 << blkbits; 220 sector_t next_block; 221 sector_t block_in_file; 222 sector_t last_block; 223 sector_t last_block_in_file; 224 sector_t blocks[MAX_BUF_PER_PAGE]; 225 unsigned page_block; 226 struct block_device *bdev = inode->i_sb->s_bdev; 227 int length; 228 unsigned relative_block = 0; 229 struct ext4_map_blocks map; 230 unsigned int nr_pages = rac ? readahead_count(rac) : 1; 231 232 map.m_pblk = 0; 233 map.m_lblk = 0; 234 map.m_len = 0; 235 map.m_flags = 0; 236 237 for (; nr_pages; nr_pages--) { 238 int fully_mapped = 1; 239 unsigned first_hole = blocks_per_page; 240 241 if (rac) 242 folio = readahead_folio(rac); 243 prefetchw(&folio->flags); 244 245 if (folio_buffers(folio)) 246 goto confused; 247 248 block_in_file = next_block = 249 (sector_t)folio->index << (PAGE_SHIFT - blkbits); 250 last_block = block_in_file + nr_pages * blocks_per_page; 251 last_block_in_file = (ext4_readpage_limit(inode) + 252 blocksize - 1) >> blkbits; 253 if (last_block > last_block_in_file) 254 last_block = last_block_in_file; 255 page_block = 0; 256 257 /* 258 * Map blocks using the previous result first. 259 */ 260 if ((map.m_flags & EXT4_MAP_MAPPED) && 261 block_in_file > map.m_lblk && 262 block_in_file < (map.m_lblk + map.m_len)) { 263 unsigned map_offset = block_in_file - map.m_lblk; 264 unsigned last = map.m_len - map_offset; 265 266 for (relative_block = 0; ; relative_block++) { 267 if (relative_block == last) { 268 /* needed? */ 269 map.m_flags &= ~EXT4_MAP_MAPPED; 270 break; 271 } 272 if (page_block == blocks_per_page) 273 break; 274 blocks[page_block] = map.m_pblk + map_offset + 275 relative_block; 276 page_block++; 277 block_in_file++; 278 } 279 } 280 281 /* 282 * Then do more ext4_map_blocks() calls until we are 283 * done with this folio. 284 */ 285 while (page_block < blocks_per_page) { 286 if (block_in_file < last_block) { 287 map.m_lblk = block_in_file; 288 map.m_len = last_block - block_in_file; 289 290 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { 291 set_error_page: 292 folio_zero_segment(folio, 0, 293 folio_size(folio)); 294 folio_unlock(folio); 295 goto next_page; 296 } 297 } 298 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { 299 fully_mapped = 0; 300 if (first_hole == blocks_per_page) 301 first_hole = page_block; 302 page_block++; 303 block_in_file++; 304 continue; 305 } 306 if (first_hole != blocks_per_page) 307 goto confused; /* hole -> non-hole */ 308 309 /* Contiguous blocks? */ 310 if (page_block && blocks[page_block-1] != map.m_pblk-1) 311 goto confused; 312 for (relative_block = 0; ; relative_block++) { 313 if (relative_block == map.m_len) { 314 /* needed? */ 315 map.m_flags &= ~EXT4_MAP_MAPPED; 316 break; 317 } else if (page_block == blocks_per_page) 318 break; 319 blocks[page_block] = map.m_pblk+relative_block; 320 page_block++; 321 block_in_file++; 322 } 323 } 324 if (first_hole != blocks_per_page) { 325 folio_zero_segment(folio, first_hole << blkbits, 326 folio_size(folio)); 327 if (first_hole == 0) { 328 if (ext4_need_verity(inode, folio->index) && 329 !fsverity_verify_folio(folio)) 330 goto set_error_page; 331 folio_end_read(folio, true); 332 continue; 333 } 334 } else if (fully_mapped) { 335 folio_set_mappedtodisk(folio); 336 } 337 338 /* 339 * This folio will go to BIO. Do we need to send this 340 * BIO off first? 341 */ 342 if (bio && (last_block_in_bio != blocks[0] - 1 || 343 !fscrypt_mergeable_bio(bio, inode, next_block))) { 344 submit_and_realloc: 345 submit_bio(bio); 346 bio = NULL; 347 } 348 if (bio == NULL) { 349 /* 350 * bio_alloc will _always_ be able to allocate a bio if 351 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 352 */ 353 bio = bio_alloc(bdev, bio_max_segs(nr_pages), 354 REQ_OP_READ, GFP_KERNEL); 355 fscrypt_set_bio_crypt_ctx(bio, inode, next_block, 356 GFP_KERNEL); 357 ext4_set_bio_post_read_ctx(bio, inode, folio->index); 358 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); 359 bio->bi_end_io = mpage_end_io; 360 if (rac) 361 bio->bi_opf |= REQ_RAHEAD; 362 } 363 364 length = first_hole << blkbits; 365 if (!bio_add_folio(bio, folio, length, 0)) 366 goto submit_and_realloc; 367 368 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 369 (relative_block == map.m_len)) || 370 (first_hole != blocks_per_page)) { 371 submit_bio(bio); 372 bio = NULL; 373 } else 374 last_block_in_bio = blocks[blocks_per_page - 1]; 375 continue; 376 confused: 377 if (bio) { 378 submit_bio(bio); 379 bio = NULL; 380 } 381 if (!folio_test_uptodate(folio)) 382 block_read_full_folio(folio, ext4_get_block); 383 else 384 folio_unlock(folio); 385 next_page: 386 ; /* A label shall be followed by a statement until C23 */ 387 } 388 if (bio) 389 submit_bio(bio); 390 return 0; 391 } 392 393 int __init ext4_init_post_read_processing(void) 394 { 395 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT); 396 397 if (!bio_post_read_ctx_cache) 398 goto fail; 399 bio_post_read_ctx_pool = 400 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 401 bio_post_read_ctx_cache); 402 if (!bio_post_read_ctx_pool) 403 goto fail_free_cache; 404 return 0; 405 406 fail_free_cache: 407 kmem_cache_destroy(bio_post_read_ctx_cache); 408 fail: 409 return -ENOMEM; 410 } 411 412 void ext4_exit_post_read_processing(void) 413 { 414 mempool_destroy(bio_post_read_ctx_pool); 415 kmem_cache_destroy(bio_post_read_ctx_cache); 416 } 417