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-rw-r--r--fs/ext4/readpage.c435
1 files changed, 435 insertions, 0 deletions
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
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+++ b/fs/ext4/readpage.c
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+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/ext4/readpage.c
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This was originally taken from fs/mpage.c
+ *
+ * The ext4_mpage_readpages() function here is intended to
+ * replace mpage_readahead() in the general case, not just for
+ * encrypted files. It has some limitations (see below), where it
+ * will fall back to read_block_full_page(), but these limitations
+ * should only be hit when page_size != block_size.
+ *
+ * This will allow us to attach a callback function to support ext4
+ * encryption.
+ *
+ * If anything unusual happens, such as:
+ *
+ * - encountering a page which has buffers
+ * - encountering a page which has a non-hole after a hole
+ * - encountering a page with non-contiguous blocks
+ *
+ * then this code just gives up and calls the buffer_head-based read function.
+ * It does handle a page which has holes at the end - that is a common case:
+ * the end-of-file on blocksize < PAGE_SIZE setups.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/kdev_t.h>
+#include <linux/gfp.h>
+#include <linux/bio.h>
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include <linux/blkdev.h>
+#include <linux/highmem.h>
+#include <linux/prefetch.h>
+#include <linux/mpage.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+
+#include "ext4.h"
+
+#define NUM_PREALLOC_POST_READ_CTXS 128
+
+static struct kmem_cache *bio_post_read_ctx_cache;
+static mempool_t *bio_post_read_ctx_pool;
+
+/* postprocessing steps for read bios */
+enum bio_post_read_step {
+ STEP_INITIAL = 0,
+ STEP_DECRYPT,
+ STEP_VERITY,
+ STEP_MAX,
+};
+
+struct bio_post_read_ctx {
+ struct bio *bio;
+ struct work_struct work;
+ unsigned int cur_step;
+ unsigned int enabled_steps;
+};
+
+static void __read_end_io(struct bio *bio)
+{
+ struct page *page;
+ struct bio_vec *bv;
+ struct bvec_iter_all iter_all;
+
+ bio_for_each_segment_all(bv, bio, iter_all) {
+ page = bv->bv_page;
+
+ /* PG_error was set if verity failed. */
+ if (bio->bi_status || PageError(page)) {
+ ClearPageUptodate(page);
+ /* will re-read again later */
+ ClearPageError(page);
+ } else {
+ SetPageUptodate(page);
+ }
+ unlock_page(page);
+ }
+ if (bio->bi_private)
+ mempool_free(bio->bi_private, bio_post_read_ctx_pool);
+ bio_put(bio);
+}
+
+static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
+
+static void decrypt_work(struct work_struct *work)
+{
+ struct bio_post_read_ctx *ctx =
+ container_of(work, struct bio_post_read_ctx, work);
+ struct bio *bio = ctx->bio;
+
+ if (fscrypt_decrypt_bio(bio))
+ bio_post_read_processing(ctx);
+ else
+ __read_end_io(bio);
+}
+
+static void verity_work(struct work_struct *work)
+{
+ struct bio_post_read_ctx *ctx =
+ container_of(work, struct bio_post_read_ctx, work);
+ struct bio *bio = ctx->bio;
+
+ /*
+ * fsverity_verify_bio() may call readahead() again, and although verity
+ * will be disabled for that, decryption may still be needed, causing
+ * another bio_post_read_ctx to be allocated. So to guarantee that
+ * mempool_alloc() never deadlocks we must free the current ctx first.
+ * This is safe because verity is the last post-read step.
+ */
+ BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
+ mempool_free(ctx, bio_post_read_ctx_pool);
+ bio->bi_private = NULL;
+
+ fsverity_verify_bio(bio);
+
+ __read_end_io(bio);
+}
+
+static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
+{
+ /*
+ * We use different work queues for decryption and for verity because
+ * verity may require reading metadata pages that need decryption, and
+ * we shouldn't recurse to the same workqueue.
+ */
+ switch (++ctx->cur_step) {
+ case STEP_DECRYPT:
+ if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
+ INIT_WORK(&ctx->work, decrypt_work);
+ fscrypt_enqueue_decrypt_work(&ctx->work);
+ return;
+ }
+ ctx->cur_step++;
+ fallthrough;
+ case STEP_VERITY:
+ if (ctx->enabled_steps & (1 << STEP_VERITY)) {
+ INIT_WORK(&ctx->work, verity_work);
+ fsverity_enqueue_verify_work(&ctx->work);
+ return;
+ }
+ ctx->cur_step++;
+ fallthrough;
+ default:
+ __read_end_io(ctx->bio);
+ }
+}
+
+static bool bio_post_read_required(struct bio *bio)
+{
+ return bio->bi_private && !bio->bi_status;
+}
+
+/*
+ * I/O completion handler for multipage BIOs.
+ *
+ * The mpage code never puts partial pages into a BIO (except for end-of-file).
+ * If a page does not map to a contiguous run of blocks then it simply falls
+ * back to block_read_full_folio().
+ *
+ * Why is this? If a page's completion depends on a number of different BIOs
+ * which can complete in any order (or at the same time) then determining the
+ * status of that page is hard. See end_buffer_async_read() for the details.
+ * There is no point in duplicating all that complexity.
+ */
+static void mpage_end_io(struct bio *bio)
+{
+ if (bio_post_read_required(bio)) {
+ struct bio_post_read_ctx *ctx = bio->bi_private;
+
+ ctx->cur_step = STEP_INITIAL;
+ bio_post_read_processing(ctx);
+ return;
+ }
+ __read_end_io(bio);
+}
+
+static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
+{
+ return fsverity_active(inode) &&
+ idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
+}
+
+static void ext4_set_bio_post_read_ctx(struct bio *bio,
+ const struct inode *inode,
+ pgoff_t first_idx)
+{
+ unsigned int post_read_steps = 0;
+
+ if (fscrypt_inode_uses_fs_layer_crypto(inode))
+ post_read_steps |= 1 << STEP_DECRYPT;
+
+ if (ext4_need_verity(inode, first_idx))
+ post_read_steps |= 1 << STEP_VERITY;
+
+ if (post_read_steps) {
+ /* Due to the mempool, this never fails. */
+ struct bio_post_read_ctx *ctx =
+ mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
+
+ ctx->bio = bio;
+ ctx->enabled_steps = post_read_steps;
+ bio->bi_private = ctx;
+ }
+}
+
+static inline loff_t ext4_readpage_limit(struct inode *inode)
+{
+ if (IS_ENABLED(CONFIG_FS_VERITY) &&
+ (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
+ return inode->i_sb->s_maxbytes;
+
+ return i_size_read(inode);
+}
+
+int ext4_mpage_readpages(struct inode *inode,
+ struct readahead_control *rac, struct page *page)
+{
+ struct bio *bio = NULL;
+ sector_t last_block_in_bio = 0;
+
+ const unsigned blkbits = inode->i_blkbits;
+ const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+ const unsigned blocksize = 1 << blkbits;
+ sector_t next_block;
+ sector_t block_in_file;
+ sector_t last_block;
+ sector_t last_block_in_file;
+ sector_t blocks[MAX_BUF_PER_PAGE];
+ unsigned page_block;
+ struct block_device *bdev = inode->i_sb->s_bdev;
+ int length;
+ unsigned relative_block = 0;
+ struct ext4_map_blocks map;
+ unsigned int nr_pages = rac ? readahead_count(rac) : 1;
+
+ map.m_pblk = 0;
+ map.m_lblk = 0;
+ map.m_len = 0;
+ map.m_flags = 0;
+
+ for (; nr_pages; nr_pages--) {
+ int fully_mapped = 1;
+ unsigned first_hole = blocks_per_page;
+
+ if (rac) {
+ page = readahead_page(rac);
+ prefetchw(&page->flags);
+ }
+
+ if (page_has_buffers(page))
+ goto confused;
+
+ block_in_file = next_block =
+ (sector_t)page->index << (PAGE_SHIFT - blkbits);
+ last_block = block_in_file + nr_pages * blocks_per_page;
+ last_block_in_file = (ext4_readpage_limit(inode) +
+ blocksize - 1) >> blkbits;
+ if (last_block > last_block_in_file)
+ last_block = last_block_in_file;
+ page_block = 0;
+
+ /*
+ * Map blocks using the previous result first.
+ */
+ if ((map.m_flags & EXT4_MAP_MAPPED) &&
+ block_in_file > map.m_lblk &&
+ block_in_file < (map.m_lblk + map.m_len)) {
+ unsigned map_offset = block_in_file - map.m_lblk;
+ unsigned last = map.m_len - map_offset;
+
+ for (relative_block = 0; ; relative_block++) {
+ if (relative_block == last) {
+ /* needed? */
+ map.m_flags &= ~EXT4_MAP_MAPPED;
+ break;
+ }
+ if (page_block == blocks_per_page)
+ break;
+ blocks[page_block] = map.m_pblk + map_offset +
+ relative_block;
+ page_block++;
+ block_in_file++;
+ }
+ }
+
+ /*
+ * Then do more ext4_map_blocks() calls until we are
+ * done with this page.
+ */
+ while (page_block < blocks_per_page) {
+ if (block_in_file < last_block) {
+ map.m_lblk = block_in_file;
+ map.m_len = last_block - block_in_file;
+
+ if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
+ set_error_page:
+ SetPageError(page);
+ zero_user_segment(page, 0,
+ PAGE_SIZE);
+ unlock_page(page);
+ goto next_page;
+ }
+ }
+ if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
+ fully_mapped = 0;
+ if (first_hole == blocks_per_page)
+ first_hole = page_block;
+ page_block++;
+ block_in_file++;
+ continue;
+ }
+ if (first_hole != blocks_per_page)
+ goto confused; /* hole -> non-hole */
+
+ /* Contiguous blocks? */
+ if (page_block && blocks[page_block-1] != map.m_pblk-1)
+ goto confused;
+ for (relative_block = 0; ; relative_block++) {
+ if (relative_block == map.m_len) {
+ /* needed? */
+ map.m_flags &= ~EXT4_MAP_MAPPED;
+ break;
+ } else if (page_block == blocks_per_page)
+ break;
+ blocks[page_block] = map.m_pblk+relative_block;
+ page_block++;
+ block_in_file++;
+ }
+ }
+ if (first_hole != blocks_per_page) {
+ zero_user_segment(page, first_hole << blkbits,
+ PAGE_SIZE);
+ if (first_hole == 0) {
+ if (ext4_need_verity(inode, page->index) &&
+ !fsverity_verify_page(page))
+ goto set_error_page;
+ SetPageUptodate(page);
+ unlock_page(page);
+ goto next_page;
+ }
+ } else if (fully_mapped) {
+ SetPageMappedToDisk(page);
+ }
+
+ /*
+ * This page will go to BIO. Do we need to send this
+ * BIO off first?
+ */
+ if (bio && (last_block_in_bio != blocks[0] - 1 ||
+ !fscrypt_mergeable_bio(bio, inode, next_block))) {
+ submit_and_realloc:
+ submit_bio(bio);
+ bio = NULL;
+ }
+ if (bio == NULL) {
+ /*
+ * bio_alloc will _always_ be able to allocate a bio if
+ * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
+ */
+ bio = bio_alloc(bdev, bio_max_segs(nr_pages),
+ REQ_OP_READ, GFP_KERNEL);
+ fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
+ GFP_KERNEL);
+ ext4_set_bio_post_read_ctx(bio, inode, page->index);
+ bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+ bio->bi_end_io = mpage_end_io;
+ if (rac)
+ bio->bi_opf |= REQ_RAHEAD;
+ }
+
+ length = first_hole << blkbits;
+ if (bio_add_page(bio, page, length, 0) < length)
+ goto submit_and_realloc;
+
+ if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
+ (relative_block == map.m_len)) ||
+ (first_hole != blocks_per_page)) {
+ submit_bio(bio);
+ bio = NULL;
+ } else
+ last_block_in_bio = blocks[blocks_per_page - 1];
+ goto next_page;
+ confused:
+ if (bio) {
+ submit_bio(bio);
+ bio = NULL;
+ }
+ if (!PageUptodate(page))
+ block_read_full_folio(page_folio(page), ext4_get_block);
+ else
+ unlock_page(page);
+ next_page:
+ if (rac)
+ put_page(page);
+ }
+ if (bio)
+ submit_bio(bio);
+ return 0;
+}
+
+int __init ext4_init_post_read_processing(void)
+{
+ bio_post_read_ctx_cache =
+ kmem_cache_create("ext4_bio_post_read_ctx",
+ sizeof(struct bio_post_read_ctx), 0, 0, NULL);
+ if (!bio_post_read_ctx_cache)
+ goto fail;
+ bio_post_read_ctx_pool =
+ mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
+ bio_post_read_ctx_cache);
+ if (!bio_post_read_ctx_pool)
+ goto fail_free_cache;
+ return 0;
+
+fail_free_cache:
+ kmem_cache_destroy(bio_post_read_ctx_cache);
+fail:
+ return -ENOMEM;
+}
+
+void ext4_exit_post_read_processing(void)
+{
+ mempool_destroy(bio_post_read_ctx_pool);
+ kmem_cache_destroy(bio_post_read_ctx_cache);
+}
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