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 #include <linux/cleancache.h> 47 48 #include "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 work_struct work; 66 unsigned int cur_step; 67 unsigned int enabled_steps; 68 }; 69 70 static void __read_end_io(struct bio *bio) 71 { 72 struct page *page; 73 struct bio_vec *bv; 74 struct bvec_iter_all iter_all; 75 76 bio_for_each_segment_all(bv, bio, iter_all) { 77 page = bv->bv_page; 78 79 /* PG_error was set if any post_read step failed */ 80 if (bio->bi_status || PageError(page)) { 81 ClearPageUptodate(page); 82 /* will re-read again later */ 83 ClearPageError(page); 84 } else { 85 SetPageUptodate(page); 86 } 87 unlock_page(page); 88 } 89 if (bio->bi_private) 90 mempool_free(bio->bi_private, bio_post_read_ctx_pool); 91 bio_put(bio); 92 } 93 94 static void bio_post_read_processing(struct bio_post_read_ctx *ctx); 95 96 static void decrypt_work(struct work_struct *work) 97 { 98 struct bio_post_read_ctx *ctx = 99 container_of(work, struct bio_post_read_ctx, work); 100 101 fscrypt_decrypt_bio(ctx->bio); 102 103 bio_post_read_processing(ctx); 104 } 105 106 static void verity_work(struct work_struct *work) 107 { 108 struct bio_post_read_ctx *ctx = 109 container_of(work, struct bio_post_read_ctx, work); 110 struct bio *bio = ctx->bio; 111 112 /* 113 * fsverity_verify_bio() may call readpages() again, and although verity 114 * will be disabled for that, decryption may still be needed, causing 115 * another bio_post_read_ctx to be allocated. So to guarantee that 116 * mempool_alloc() never deadlocks we must free the current ctx first. 117 * This is safe because verity is the last post-read step. 118 */ 119 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX); 120 mempool_free(ctx, bio_post_read_ctx_pool); 121 bio->bi_private = NULL; 122 123 fsverity_verify_bio(bio); 124 125 __read_end_io(bio); 126 } 127 128 static void bio_post_read_processing(struct bio_post_read_ctx *ctx) 129 { 130 /* 131 * We use different work queues for decryption and for verity because 132 * verity may require reading metadata pages that need decryption, and 133 * we shouldn't recurse to the same workqueue. 134 */ 135 switch (++ctx->cur_step) { 136 case STEP_DECRYPT: 137 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) { 138 INIT_WORK(&ctx->work, decrypt_work); 139 fscrypt_enqueue_decrypt_work(&ctx->work); 140 return; 141 } 142 ctx->cur_step++; 143 fallthrough; 144 case STEP_VERITY: 145 if (ctx->enabled_steps & (1 << STEP_VERITY)) { 146 INIT_WORK(&ctx->work, verity_work); 147 fsverity_enqueue_verify_work(&ctx->work); 148 return; 149 } 150 ctx->cur_step++; 151 fallthrough; 152 default: 153 __read_end_io(ctx->bio); 154 } 155 } 156 157 static bool bio_post_read_required(struct bio *bio) 158 { 159 return bio->bi_private && !bio->bi_status; 160 } 161 162 /* 163 * I/O completion handler for multipage BIOs. 164 * 165 * The mpage code never puts partial pages into a BIO (except for end-of-file). 166 * If a page does not map to a contiguous run of blocks then it simply falls 167 * back to block_read_full_page(). 168 * 169 * Why is this? If a page's completion depends on a number of different BIOs 170 * which can complete in any order (or at the same time) then determining the 171 * status of that page is hard. See end_buffer_async_read() for the details. 172 * There is no point in duplicating all that complexity. 173 */ 174 static void mpage_end_io(struct bio *bio) 175 { 176 if (bio_post_read_required(bio)) { 177 struct bio_post_read_ctx *ctx = bio->bi_private; 178 179 ctx->cur_step = STEP_INITIAL; 180 bio_post_read_processing(ctx); 181 return; 182 } 183 __read_end_io(bio); 184 } 185 186 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx) 187 { 188 return fsverity_active(inode) && 189 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE); 190 } 191 192 static void ext4_set_bio_post_read_ctx(struct bio *bio, 193 const struct inode *inode, 194 pgoff_t first_idx) 195 { 196 unsigned int post_read_steps = 0; 197 198 if (fscrypt_inode_uses_fs_layer_crypto(inode)) 199 post_read_steps |= 1 << STEP_DECRYPT; 200 201 if (ext4_need_verity(inode, first_idx)) 202 post_read_steps |= 1 << STEP_VERITY; 203 204 if (post_read_steps) { 205 /* Due to the mempool, this never fails. */ 206 struct bio_post_read_ctx *ctx = 207 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS); 208 209 ctx->bio = bio; 210 ctx->enabled_steps = post_read_steps; 211 bio->bi_private = ctx; 212 } 213 } 214 215 static inline loff_t ext4_readpage_limit(struct inode *inode) 216 { 217 if (IS_ENABLED(CONFIG_FS_VERITY) && 218 (IS_VERITY(inode) || ext4_verity_in_progress(inode))) 219 return inode->i_sb->s_maxbytes; 220 221 return i_size_read(inode); 222 } 223 224 int ext4_mpage_readpages(struct inode *inode, 225 struct readahead_control *rac, struct page *page) 226 { 227 struct bio *bio = NULL; 228 sector_t last_block_in_bio = 0; 229 230 const unsigned blkbits = inode->i_blkbits; 231 const unsigned blocks_per_page = PAGE_SIZE >> blkbits; 232 const unsigned blocksize = 1 << blkbits; 233 sector_t next_block; 234 sector_t block_in_file; 235 sector_t last_block; 236 sector_t last_block_in_file; 237 sector_t blocks[MAX_BUF_PER_PAGE]; 238 unsigned page_block; 239 struct block_device *bdev = inode->i_sb->s_bdev; 240 int length; 241 unsigned relative_block = 0; 242 struct ext4_map_blocks map; 243 unsigned int nr_pages = rac ? readahead_count(rac) : 1; 244 245 map.m_pblk = 0; 246 map.m_lblk = 0; 247 map.m_len = 0; 248 map.m_flags = 0; 249 250 for (; nr_pages; nr_pages--) { 251 int fully_mapped = 1; 252 unsigned first_hole = blocks_per_page; 253 254 if (rac) { 255 page = readahead_page(rac); 256 prefetchw(&page->flags); 257 } 258 259 if (page_has_buffers(page)) 260 goto confused; 261 262 block_in_file = next_block = 263 (sector_t)page->index << (PAGE_SHIFT - blkbits); 264 last_block = block_in_file + nr_pages * blocks_per_page; 265 last_block_in_file = (ext4_readpage_limit(inode) + 266 blocksize - 1) >> blkbits; 267 if (last_block > last_block_in_file) 268 last_block = last_block_in_file; 269 page_block = 0; 270 271 /* 272 * Map blocks using the previous result first. 273 */ 274 if ((map.m_flags & EXT4_MAP_MAPPED) && 275 block_in_file > map.m_lblk && 276 block_in_file < (map.m_lblk + map.m_len)) { 277 unsigned map_offset = block_in_file - map.m_lblk; 278 unsigned last = map.m_len - map_offset; 279 280 for (relative_block = 0; ; relative_block++) { 281 if (relative_block == last) { 282 /* needed? */ 283 map.m_flags &= ~EXT4_MAP_MAPPED; 284 break; 285 } 286 if (page_block == blocks_per_page) 287 break; 288 blocks[page_block] = map.m_pblk + map_offset + 289 relative_block; 290 page_block++; 291 block_in_file++; 292 } 293 } 294 295 /* 296 * Then do more ext4_map_blocks() calls until we are 297 * done with this page. 298 */ 299 while (page_block < blocks_per_page) { 300 if (block_in_file < last_block) { 301 map.m_lblk = block_in_file; 302 map.m_len = last_block - block_in_file; 303 304 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { 305 set_error_page: 306 SetPageError(page); 307 zero_user_segment(page, 0, 308 PAGE_SIZE); 309 unlock_page(page); 310 goto next_page; 311 } 312 } 313 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { 314 fully_mapped = 0; 315 if (first_hole == blocks_per_page) 316 first_hole = page_block; 317 page_block++; 318 block_in_file++; 319 continue; 320 } 321 if (first_hole != blocks_per_page) 322 goto confused; /* hole -> non-hole */ 323 324 /* Contiguous blocks? */ 325 if (page_block && blocks[page_block-1] != map.m_pblk-1) 326 goto confused; 327 for (relative_block = 0; ; relative_block++) { 328 if (relative_block == map.m_len) { 329 /* needed? */ 330 map.m_flags &= ~EXT4_MAP_MAPPED; 331 break; 332 } else if (page_block == blocks_per_page) 333 break; 334 blocks[page_block] = map.m_pblk+relative_block; 335 page_block++; 336 block_in_file++; 337 } 338 } 339 if (first_hole != blocks_per_page) { 340 zero_user_segment(page, first_hole << blkbits, 341 PAGE_SIZE); 342 if (first_hole == 0) { 343 if (ext4_need_verity(inode, page->index) && 344 !fsverity_verify_page(page)) 345 goto set_error_page; 346 SetPageUptodate(page); 347 unlock_page(page); 348 goto next_page; 349 } 350 } else if (fully_mapped) { 351 SetPageMappedToDisk(page); 352 } 353 if (fully_mapped && blocks_per_page == 1 && 354 !PageUptodate(page) && cleancache_get_page(page) == 0) { 355 SetPageUptodate(page); 356 goto confused; 357 } 358 359 /* 360 * This page will go to BIO. Do we need to send this 361 * BIO off first? 362 */ 363 if (bio && (last_block_in_bio != blocks[0] - 1 || 364 !fscrypt_mergeable_bio(bio, inode, next_block))) { 365 submit_and_realloc: 366 submit_bio(bio); 367 bio = NULL; 368 } 369 if (bio == NULL) { 370 /* 371 * bio_alloc will _always_ be able to allocate a bio if 372 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 373 */ 374 bio = bio_alloc(GFP_KERNEL, bio_max_segs(nr_pages)); 375 fscrypt_set_bio_crypt_ctx(bio, inode, next_block, 376 GFP_KERNEL); 377 ext4_set_bio_post_read_ctx(bio, inode, page->index); 378 bio_set_dev(bio, bdev); 379 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); 380 bio->bi_end_io = mpage_end_io; 381 bio_set_op_attrs(bio, REQ_OP_READ, 382 rac ? REQ_RAHEAD : 0); 383 } 384 385 length = first_hole << blkbits; 386 if (bio_add_page(bio, page, length, 0) < length) 387 goto submit_and_realloc; 388 389 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 390 (relative_block == map.m_len)) || 391 (first_hole != blocks_per_page)) { 392 submit_bio(bio); 393 bio = NULL; 394 } else 395 last_block_in_bio = blocks[blocks_per_page - 1]; 396 goto next_page; 397 confused: 398 if (bio) { 399 submit_bio(bio); 400 bio = NULL; 401 } 402 if (!PageUptodate(page)) 403 block_read_full_page(page, ext4_get_block); 404 else 405 unlock_page(page); 406 next_page: 407 if (rac) 408 put_page(page); 409 } 410 if (bio) 411 submit_bio(bio); 412 return 0; 413 } 414 415 int __init ext4_init_post_read_processing(void) 416 { 417 bio_post_read_ctx_cache = 418 kmem_cache_create("ext4_bio_post_read_ctx", 419 sizeof(struct bio_post_read_ctx), 0, 0, NULL); 420 if (!bio_post_read_ctx_cache) 421 goto fail; 422 bio_post_read_ctx_pool = 423 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 424 bio_post_read_ctx_cache); 425 if (!bio_post_read_ctx_pool) 426 goto fail_free_cache; 427 return 0; 428 429 fail_free_cache: 430 kmem_cache_destroy(bio_post_read_ctx_cache); 431 fail: 432 return -ENOMEM; 433 } 434 435 void ext4_exit_post_read_processing(void) 436 { 437 mempool_destroy(bio_post_read_ctx_pool); 438 kmem_cache_destroy(bio_post_read_ctx_cache); 439 } 440