1 files changed, 409 insertions, 0 deletions

diff --git a/fs/verity/verify.c b/fs/verity/verify.c
new file mode 100644
index 000000000..f50e3b5b5
--- /dev/null
+++ b/fs/verity/verify.c
@@ -0,0 +1,409 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Data verification functions, i.e. hooks for ->readahead()
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <crypto/hash.h>
+#include <linux/bio.h>
+
+static struct workqueue_struct *fsverity_read_workqueue;
+
+static inline int cmp_hashes(const struct fsverity_info *vi,
+			     const u8 *want_hash, const u8 *real_hash,
+			     u64 data_pos, int level)
+{
+	const unsigned int hsize = vi->tree_params.digest_size;
+
+	if (memcmp(want_hash, real_hash, hsize) == 0)
+		return 0;
+
+	fsverity_err(vi->inode,
+		     "FILE CORRUPTED! pos=%llu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
+		     data_pos, level,
+		     vi->tree_params.hash_alg->name, hsize, want_hash,
+		     vi->tree_params.hash_alg->name, hsize, real_hash);
+	return -EBADMSG;
+}
+
+static bool data_is_zeroed(struct inode *inode, struct page *page,
+			   unsigned int len, unsigned int offset)
+{
+	void *virt = kmap_local_page(page);
+
+	if (memchr_inv(virt + offset, 0, len)) {
+		kunmap_local(virt);
+		fsverity_err(inode,
+			     "FILE CORRUPTED!  Data past EOF is not zeroed");
+		return false;
+	}
+	kunmap_local(virt);
+	return true;
+}
+
+/*
+ * Returns true if the hash block with index @hblock_idx in the tree, located in
+ * @hpage, has already been verified.
+ */
+static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
+				   unsigned long hblock_idx)
+{
+	bool verified;
+	unsigned int blocks_per_page;
+	unsigned int i;
+
+	/*
+	 * When the Merkle tree block size and page size are the same, then the
+	 * ->hash_block_verified bitmap isn't allocated, and we use PG_checked
+	 * to directly indicate whether the page's block has been verified.
+	 *
+	 * Using PG_checked also guarantees that we re-verify hash pages that
+	 * get evicted and re-instantiated from the backing storage, as new
+	 * pages always start out with PG_checked cleared.
+	 */
+	if (!vi->hash_block_verified)
+		return PageChecked(hpage);
+
+	/*
+	 * When the Merkle tree block size and page size differ, we use a bitmap
+	 * to indicate whether each hash block has been verified.
+	 *
+	 * However, we still need to ensure that hash pages that get evicted and
+	 * re-instantiated from the backing storage are re-verified.  To do
+	 * this, we use PG_checked again, but now it doesn't really mean
+	 * "checked".  Instead, now it just serves as an indicator for whether
+	 * the hash page is newly instantiated or not.
+	 *
+	 * The first thread that sees PG_checked=0 must clear the corresponding
+	 * bitmap bits, then set PG_checked=1.  This requires a spinlock.  To
+	 * avoid having to take this spinlock in the common case of
+	 * PG_checked=1, we start with an opportunistic lockless read.
+	 */
+	if (PageChecked(hpage)) {
+		/*
+		 * A read memory barrier is needed here to give ACQUIRE
+		 * semantics to the above PageChecked() test.
+		 */
+		smp_rmb();
+		return test_bit(hblock_idx, vi->hash_block_verified);
+	}
+	spin_lock(&vi->hash_page_init_lock);
+	if (PageChecked(hpage)) {
+		verified = test_bit(hblock_idx, vi->hash_block_verified);
+	} else {
+		blocks_per_page = vi->tree_params.blocks_per_page;
+		hblock_idx = round_down(hblock_idx, blocks_per_page);
+		for (i = 0; i < blocks_per_page; i++)
+			clear_bit(hblock_idx + i, vi->hash_block_verified);
+		/*
+		 * A write memory barrier is needed here to give RELEASE
+		 * semantics to the below SetPageChecked() operation.
+		 */
+		smp_wmb();
+		SetPageChecked(hpage);
+		verified = false;
+	}
+	spin_unlock(&vi->hash_page_init_lock);
+	return verified;
+}
+
+/*
+ * Verify a single data block against the file's Merkle tree.
+ *
+ * In principle, we need to verify the entire path to the root node.  However,
+ * for efficiency the filesystem may cache the hash blocks.  Therefore we need
+ * only ascend the tree until an already-verified hash block is seen, and then
+ * verify the path to that block.
+ *
+ * Return: %true if the data block is valid, else %false.
+ */
+static bool
+verify_data_block(struct inode *inode, struct fsverity_info *vi,
+		  struct ahash_request *req, struct page *data_page,
+		  u64 data_pos, unsigned int dblock_offset_in_page,
+		  unsigned long max_ra_pages)
+{
+	const struct merkle_tree_params *params = &vi->tree_params;
+	const unsigned int hsize = params->digest_size;
+	int level;
+	u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
+	const u8 *want_hash;
+	u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
+	/* The hash blocks that are traversed, indexed by level */
+	struct {
+		/* Page containing the hash block */
+		struct page *page;
+		/* Index of the hash block in the tree overall */
+		unsigned long index;
+		/* Byte offset of the hash block within @page */
+		unsigned int offset_in_page;
+		/* Byte offset of the wanted hash within @page */
+		unsigned int hoffset;
+	} hblocks[FS_VERITY_MAX_LEVELS];
+	/*
+	 * The index of the previous level's block within that level; also the
+	 * index of that block's hash within the current level.
+	 */
+	u64 hidx = data_pos >> params->log_blocksize;
+	int err;
+
+	if (unlikely(data_pos >= inode->i_size)) {
+		/*
+		 * This can happen in the data page spanning EOF when the Merkle
+		 * tree block size is less than the page size.  The Merkle tree
+		 * doesn't cover data blocks fully past EOF.  But the entire
+		 * page spanning EOF can be visible to userspace via a mmap, and
+		 * any part past EOF should be all zeroes.  Therefore, we need
+		 * to verify that any data blocks fully past EOF are all zeroes.
+		 */
+		return data_is_zeroed(inode, data_page, params->block_size,
+				      dblock_offset_in_page);
+	}
+
+	/*
+	 * Starting at the leaf level, ascend the tree saving hash blocks along
+	 * the way until we find a hash block that has already been verified, or
+	 * until we reach the root.
+	 */
+	for (level = 0; level < params->num_levels; level++) {
+		unsigned long next_hidx;
+		unsigned long hblock_idx;
+		pgoff_t hpage_idx;
+		unsigned int hblock_offset_in_page;
+		unsigned int hoffset;
+		struct page *hpage;
+
+		/*
+		 * The index of the block in the current level; also the index
+		 * of that block's hash within the next level.
+		 */
+		next_hidx = hidx >> params->log_arity;
+
+		/* Index of the hash block in the tree overall */
+		hblock_idx = params->level_start[level] + next_hidx;
+
+		/* Index of the hash page in the tree overall */
+		hpage_idx = hblock_idx >> params->log_blocks_per_page;
+
+		/* Byte offset of the hash block within the page */
+		hblock_offset_in_page =
+			(hblock_idx << params->log_blocksize) & ~PAGE_MASK;
+
+		/* Byte offset of the hash within the page */
+		hoffset = hblock_offset_in_page +
+			  ((hidx << params->log_digestsize) &
+			   (params->block_size - 1));
+
+		hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode,
+				hpage_idx, level == 0 ? min(max_ra_pages,
+					params->tree_pages - hpage_idx) : 0);
+		if (IS_ERR(hpage)) {
+			err = PTR_ERR(hpage);
+			fsverity_err(inode,
+				     "Error %d reading Merkle tree page %lu",
+				     err, hpage_idx);
+			goto out;
+		}
+		if (is_hash_block_verified(vi, hpage, hblock_idx)) {
+			memcpy_from_page(_want_hash, hpage, hoffset, hsize);
+			want_hash = _want_hash;
+			put_page(hpage);
+			goto descend;
+		}
+		hblocks[level].page = hpage;
+		hblocks[level].index = hblock_idx;
+		hblocks[level].offset_in_page = hblock_offset_in_page;
+		hblocks[level].hoffset = hoffset;
+		hidx = next_hidx;
+	}
+
+	want_hash = vi->root_hash;
+descend:
+	/* Descend the tree verifying hash blocks. */
+	for (; level > 0; level--) {
+		struct page *hpage = hblocks[level - 1].page;
+		unsigned long hblock_idx = hblocks[level - 1].index;
+		unsigned int hblock_offset_in_page =
+			hblocks[level - 1].offset_in_page;
+		unsigned int hoffset = hblocks[level - 1].hoffset;
+
+		err = fsverity_hash_block(params, inode, req, hpage,
+					  hblock_offset_in_page, real_hash);
+		if (err)
+			goto out;
+		err = cmp_hashes(vi, want_hash, real_hash, data_pos, level - 1);
+		if (err)
+			goto out;
+		/*
+		 * Mark the hash block as verified.  This must be atomic and
+		 * idempotent, as the same hash block might be verified by
+		 * multiple threads concurrently.
+		 */
+		if (vi->hash_block_verified)
+			set_bit(hblock_idx, vi->hash_block_verified);
+		else
+			SetPageChecked(hpage);
+		memcpy_from_page(_want_hash, hpage, hoffset, hsize);
+		want_hash = _want_hash;
+		put_page(hpage);
+	}
+
+	/* Finally, verify the data block. */
+	err = fsverity_hash_block(params, inode, req, data_page,
+				  dblock_offset_in_page, real_hash);
+	if (err)
+		goto out;
+	err = cmp_hashes(vi, want_hash, real_hash, data_pos, -1);
+out:
+	for (; level > 0; level--)
+		put_page(hblocks[level - 1].page);
+
+	return err == 0;
+}
+
+static bool
+verify_data_blocks(struct inode *inode, struct fsverity_info *vi,
+		   struct ahash_request *req, struct folio *data_folio,
+		   size_t len, size_t offset, unsigned long max_ra_pages)
+{
+	const unsigned int block_size = vi->tree_params.block_size;
+	u64 pos = (u64)data_folio->index << PAGE_SHIFT;
+
+	if (WARN_ON_ONCE(len <= 0 || !IS_ALIGNED(len | offset, block_size)))
+		return false;
+	if (WARN_ON_ONCE(!folio_test_locked(data_folio) ||
+			 folio_test_uptodate(data_folio)))
+		return false;
+	do {
+		struct page *data_page =
+			folio_page(data_folio, offset >> PAGE_SHIFT);
+
+		if (!verify_data_block(inode, vi, req, data_page, pos + offset,
+				       offset & ~PAGE_MASK, max_ra_pages))
+			return false;
+		offset += block_size;
+		len -= block_size;
+	} while (len);
+	return true;
+}
+
+/**
+ * fsverity_verify_blocks() - verify data in a folio
+ * @folio: the folio containing the data to verify
+ * @len: the length of the data to verify in the folio
+ * @offset: the offset of the data to verify in the folio
+ *
+ * Verify data that has just been read from a verity file.  The data must be
+ * located in a pagecache folio that is still locked and not yet uptodate.  The
+ * length and offset of the data must be Merkle tree block size aligned.
+ *
+ * Return: %true if the data is valid, else %false.
+ */
+bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset)
+{
+	struct inode *inode = folio->mapping->host;
+	struct fsverity_info *vi = inode->i_verity_info;
+	struct ahash_request *req;
+	bool valid;
+
+	/* This allocation never fails, since it's mempool-backed. */
+	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
+
+	valid = verify_data_blocks(inode, vi, req, folio, len, offset, 0);
+
+	fsverity_free_hash_request(vi->tree_params.hash_alg, req);
+
+	return valid;
+}
+EXPORT_SYMBOL_GPL(fsverity_verify_blocks);
+
+#ifdef CONFIG_BLOCK
+/**
+ * fsverity_verify_bio() - verify a 'read' bio that has just completed
+ * @bio: the bio to verify
+ *
+ * Verify the bio's data against the file's Merkle tree.  All bio data segments
+ * must be aligned to the file's Merkle tree block size.  If any data fails
+ * verification, then bio->bi_status is set to an error status.
+ *
+ * This is a helper function for use by the ->readahead() method of filesystems
+ * that issue bios to read data directly into the page cache.  Filesystems that
+ * populate the page cache without issuing bios (e.g. non block-based
+ * filesystems) must instead call fsverity_verify_page() directly on each page.
+ * All filesystems must also call fsverity_verify_page() on holes.
+ */
+void fsverity_verify_bio(struct bio *bio)
+{
+	struct inode *inode = bio_first_page_all(bio)->mapping->host;
+	struct fsverity_info *vi = inode->i_verity_info;
+	struct ahash_request *req;
+	struct folio_iter fi;
+	unsigned long max_ra_pages = 0;
+
+	/* This allocation never fails, since it's mempool-backed. */
+	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
+
+	if (bio->bi_opf & REQ_RAHEAD) {
+		/*
+		 * If this bio is for data readahead, then we also do readahead
+		 * of the first (largest) level of the Merkle tree.  Namely,
+		 * when a Merkle tree page is read, we also try to piggy-back on
+		 * some additional pages -- up to 1/4 the number of data pages.
+		 *
+		 * This improves sequential read performance, as it greatly
+		 * reduces the number of I/O requests made to the Merkle tree.
+		 */
+		max_ra_pages = bio->bi_iter.bi_size >> (PAGE_SHIFT + 2);
+	}
+
+	bio_for_each_folio_all(fi, bio) {
+		if (!verify_data_blocks(inode, vi, req, fi.folio, fi.length,
+					fi.offset, max_ra_pages)) {
+			bio->bi_status = BLK_STS_IOERR;
+			break;
+		}
+	}
+
+	fsverity_free_hash_request(vi->tree_params.hash_alg, req);
+}
+EXPORT_SYMBOL_GPL(fsverity_verify_bio);
+#endif /* CONFIG_BLOCK */
+
+/**
+ * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
+ * @work: the work to enqueue
+ *
+ * Enqueue verification work for asynchronous processing.
+ */
+void fsverity_enqueue_verify_work(struct work_struct *work)
+{
+	queue_work(fsverity_read_workqueue, work);
+}
+EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);
+
+int __init fsverity_init_workqueue(void)
+{
+	/*
+	 * Use an unbound workqueue to allow bios to be verified in parallel
+	 * even when they happen to complete on the same CPU.  This sacrifices
+	 * locality, but it's worthwhile since hashing is CPU-intensive.
+	 *
+	 * Also use a high-priority workqueue to prioritize verification work,
+	 * which blocks reads from completing, over regular application tasks.
+	 */
+	fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
+						  WQ_UNBOUND | WQ_HIGHPRI,
+						  num_online_cpus());
+	if (!fsverity_read_workqueue)
+		return -ENOMEM;
+	return 0;
+}
+
+void __init fsverity_exit_workqueue(void)
+{
+	destroy_workqueue(fsverity_read_workqueue);
+	fsverity_read_workqueue = NULL;
+}