diff --git a/fs/verity/Makefile b/fs/verity/Makefile
index 398f3f85fa184b..e6a8951c493a5e 100644
--- a/fs/verity/Makefile
+++ b/fs/verity/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_FS_VERITY) += hash_algs.o \
-			   init.o
+			   init.o \
+			   open.o
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index 9697aaebb5dc1f..c79746ff335e14 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -15,8 +15,7 @@
 #define pr_fmt(fmt) "fs-verity: " fmt
 
 #include <crypto/sha.h>
-#include <linux/fs.h>
-#include <uapi/linux/fsverity.h>
+#include <linux/fsverity.h>
 
 struct ahash_request;
 
@@ -59,6 +58,40 @@ struct merkle_tree_params {
 	u64 level_start[FS_VERITY_MAX_LEVELS];
 };
 
+/**
+ * fsverity_info - cached verity metadata for an inode
+ *
+ * When a verity file is first opened, an instance of this struct is allocated
+ * and stored in ->i_verity_info; it remains until the inode is evicted.  It
+ * caches information about the Merkle tree that's needed to efficiently verify
+ * data read from the file.  It also caches the file measurement.  The Merkle
+ * tree pages themselves are not cached here, but the filesystem may cache them.
+ */
+struct fsverity_info {
+	struct merkle_tree_params tree_params;
+	u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
+	u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
+	const struct inode *inode;
+};
+
+/*
+ * Merkle tree properties.  The file measurement is the hash of this structure.
+ */
+struct fsverity_descriptor {
+	__u8 version;		/* must be 1 */
+	__u8 hash_algorithm;	/* Merkle tree hash algorithm */
+	__u8 log_blocksize;	/* log2 of size of data and tree blocks */
+	__u8 salt_size;		/* size of salt in bytes; 0 if none */
+	__le32 sig_size;	/* reserved, must be 0 */
+	__le64 data_size;	/* size of file the Merkle tree is built over */
+	__u8 root_hash[64];	/* Merkle tree root hash */
+	__u8 salt[32];		/* salt prepended to each hashed block */
+	__u8 __reserved[144];	/* must be 0's */
+};
+
+/* Arbitrary limit to bound the kmalloc() size.  Can be changed. */
+#define FS_VERITY_MAX_DESCRIPTOR_SIZE	16384
+
 /* hash_algs.c */
 
 extern struct fsverity_hash_alg fsverity_hash_algs[];
@@ -85,4 +118,21 @@ fsverity_msg(const struct inode *inode, const char *level,
 #define fsverity_err(inode, fmt, ...)		\
 	fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
 
+/* open.c */
+
+int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
+				     const struct inode *inode,
+				     unsigned int hash_algorithm,
+				     unsigned int log_blocksize,
+				     const u8 *salt, size_t salt_size);
+
+struct fsverity_info *fsverity_create_info(const struct inode *inode,
+					   const void *desc, size_t desc_size);
+
+void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
+
+void fsverity_free_info(struct fsverity_info *vi);
+
+int __init fsverity_init_info_cache(void);
+
 #endif /* _FSVERITY_PRIVATE_H */
diff --git a/fs/verity/init.c b/fs/verity/init.c
index 40076bbe452a48..fff1fd6343357d 100644
--- a/fs/verity/init.c
+++ b/fs/verity/init.c
@@ -33,8 +33,14 @@ void fsverity_msg(const struct inode *inode, const char *level,
 
 static int __init fsverity_init(void)
 {
+	int err;
+
 	fsverity_check_hash_algs();
 
+	err = fsverity_init_info_cache();
+	if (err)
+		return err;
+
 	pr_debug("Initialized fs-verity\n");
 	return 0;
 }
diff --git a/fs/verity/open.c b/fs/verity/open.c
new file mode 100644
index 00000000000000..3a3bb27e23f5e3
--- /dev/null
+++ b/fs/verity/open.c
@@ -0,0 +1,319 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/open.c: opening fs-verity files
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/slab.h>
+
+static struct kmem_cache *fsverity_info_cachep;
+
+/**
+ * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
+ * @params: the parameters struct to initialize
+ * @inode: the inode for which the Merkle tree is being built
+ * @hash_algorithm: number of hash algorithm to use
+ * @log_blocksize: log base 2 of block size to use
+ * @salt: pointer to salt (optional)
+ * @salt_size: size of salt, possibly 0
+ *
+ * Validate the hash algorithm and block size, then compute the tree topology
+ * (num levels, num blocks in each level, etc.) and initialize @params.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
+				     const struct inode *inode,
+				     unsigned int hash_algorithm,
+				     unsigned int log_blocksize,
+				     const u8 *salt, size_t salt_size)
+{
+	const struct fsverity_hash_alg *hash_alg;
+	int err;
+	u64 blocks;
+	u64 offset;
+	int level;
+
+	memset(params, 0, sizeof(*params));
+
+	hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
+	if (IS_ERR(hash_alg))
+		return PTR_ERR(hash_alg);
+	params->hash_alg = hash_alg;
+	params->digest_size = hash_alg->digest_size;
+
+	params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
+							salt_size);
+	if (IS_ERR(params->hashstate)) {
+		err = PTR_ERR(params->hashstate);
+		params->hashstate = NULL;
+		fsverity_err(inode, "Error %d preparing hash state", err);
+		goto out_err;
+	}
+
+	if (log_blocksize != PAGE_SHIFT) {
+		fsverity_warn(inode, "Unsupported log_blocksize: %u",
+			      log_blocksize);
+		err = -EINVAL;
+		goto out_err;
+	}
+	params->log_blocksize = log_blocksize;
+	params->block_size = 1 << log_blocksize;
+
+	if (WARN_ON(!is_power_of_2(params->digest_size))) {
+		err = -EINVAL;
+		goto out_err;
+	}
+	if (params->block_size < 2 * params->digest_size) {
+		fsverity_warn(inode,
+			      "Merkle tree block size (%u) too small for hash algorithm \"%s\"",
+			      params->block_size, hash_alg->name);
+		err = -EINVAL;
+		goto out_err;
+	}
+	params->log_arity = params->log_blocksize - ilog2(params->digest_size);
+	params->hashes_per_block = 1 << params->log_arity;
+
+	pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
+		 hash_alg->name, params->block_size, params->hashes_per_block,
+		 (int)salt_size, salt);
+
+	/*
+	 * Compute the number of levels in the Merkle tree and create a map from
+	 * level to the starting block of that level.  Level 'num_levels - 1' is
+	 * the root and is stored first.  Level 0 is the level directly "above"
+	 * the data blocks and is stored last.
+	 */
+
+	/* Compute number of levels and the number of blocks in each level */
+	blocks = (inode->i_size + params->block_size - 1) >> log_blocksize;
+	pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
+	while (blocks > 1) {
+		if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
+			fsverity_err(inode, "Too many levels in Merkle tree");
+			err = -EINVAL;
+			goto out_err;
+		}
+		blocks = (blocks + params->hashes_per_block - 1) >>
+			 params->log_arity;
+		/* temporarily using level_start[] to store blocks in level */
+		params->level_start[params->num_levels++] = blocks;
+	}
+
+	/* Compute the starting block of each level */
+	offset = 0;
+	for (level = (int)params->num_levels - 1; level >= 0; level--) {
+		blocks = params->level_start[level];
+		params->level_start[level] = offset;
+		pr_debug("Level %d is %llu blocks starting at index %llu\n",
+			 level, blocks, offset);
+		offset += blocks;
+	}
+
+	params->tree_size = offset << log_blocksize;
+	return 0;
+
+out_err:
+	kfree(params->hashstate);
+	memset(params, 0, sizeof(*params));
+	return err;
+}
+
+/* Compute the file measurement by hashing the fsverity_descriptor. */
+static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg,
+				    const struct fsverity_descriptor *desc,
+				    u8 *measurement)
+{
+	return fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
+}
+
+/*
+ * Validate the given fsverity_descriptor and create a new fsverity_info from
+ * it.
+ */
+struct fsverity_info *fsverity_create_info(const struct inode *inode,
+					   const void *_desc, size_t desc_size)
+{
+	const struct fsverity_descriptor *desc = _desc;
+	struct fsverity_info *vi;
+	int err;
+
+	if (desc_size < sizeof(*desc)) {
+		fsverity_err(inode, "Unrecognized descriptor size (%zu)",
+			     desc_size);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (desc->version != 1) {
+		fsverity_err(inode, "Unrecognized descriptor version: %u",
+			     desc->version);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (desc->sig_size ||
+	    memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
+		fsverity_err(inode, "Reserved bits set in descriptor");
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (desc->salt_size > sizeof(desc->salt)) {
+		fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (le64_to_cpu(desc->data_size) != inode->i_size) {
+		fsverity_err(inode,
+			     "Wrong data_size: %llu (desc) != %lld (inode)",
+			     le64_to_cpu(desc->data_size), inode->i_size);
+		return ERR_PTR(-EINVAL);
+	}
+
+	vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
+	if (!vi)
+		return ERR_PTR(-ENOMEM);
+	vi->inode = inode;
+
+	err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
+					       desc->hash_algorithm,
+					       desc->log_blocksize,
+					       desc->salt, desc->salt_size);
+	if (err) {
+		fsverity_err(inode,
+			     "Error %d initializing Merkle tree parameters",
+			     err);
+		goto out;
+	}
+
+	memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
+
+	err = compute_file_measurement(vi->tree_params.hash_alg, desc,
+				       vi->measurement);
+	if (err) {
+		fsverity_err(vi->inode, "Error %d computing file measurement",
+			     err);
+		goto out;
+	}
+	pr_debug("Computed file measurement: %s:%*phN\n",
+		 vi->tree_params.hash_alg->name,
+		 vi->tree_params.digest_size, vi->measurement);
+out:
+	if (err) {
+		fsverity_free_info(vi);
+		vi = ERR_PTR(err);
+	}
+	return vi;
+}
+
+void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
+{
+	/*
+	 * Multiple processes may race to set ->i_verity_info, so use cmpxchg.
+	 * This pairs with the READ_ONCE() in fsverity_get_info().
+	 */
+	if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL)
+		fsverity_free_info(vi);
+}
+
+void fsverity_free_info(struct fsverity_info *vi)
+{
+	if (!vi)
+		return;
+	kfree(vi->tree_params.hashstate);
+	kmem_cache_free(fsverity_info_cachep, vi);
+}
+
+/* Ensure the inode has an ->i_verity_info */
+static int ensure_verity_info(struct inode *inode)
+{
+	struct fsverity_info *vi = fsverity_get_info(inode);
+	struct fsverity_descriptor *desc;
+	int res;
+
+	if (vi)
+		return 0;
+
+	res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
+	if (res < 0) {
+		fsverity_err(inode,
+			     "Error %d getting verity descriptor size", res);
+		return res;
+	}
+	if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
+		fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
+			     res);
+		return -EMSGSIZE;
+	}
+	desc = kmalloc(res, GFP_KERNEL);
+	if (!desc)
+		return -ENOMEM;
+	res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
+	if (res < 0) {
+		fsverity_err(inode, "Error %d reading verity descriptor", res);
+		goto out_free_desc;
+	}
+
+	vi = fsverity_create_info(inode, desc, res);
+	if (IS_ERR(vi)) {
+		res = PTR_ERR(vi);
+		goto out_free_desc;
+	}
+
+	fsverity_set_info(inode, vi);
+	res = 0;
+out_free_desc:
+	kfree(desc);
+	return res;
+}
+
+/**
+ * fsverity_file_open - prepare to open a verity file
+ * @inode: the inode being opened
+ * @filp: the struct file being set up
+ *
+ * When opening a verity file, deny the open if it is for writing.  Otherwise,
+ * set up the inode's ->i_verity_info if not already done.
+ *
+ * When combined with fscrypt, this must be called after fscrypt_file_open().
+ * Otherwise, we won't have the key set up to decrypt the verity metadata.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+	if (!IS_VERITY(inode))
+		return 0;
+
+	if (filp->f_mode & FMODE_WRITE) {
+		pr_debug("Denying opening verity file (ino %lu) for write\n",
+			 inode->i_ino);
+		return -EPERM;
+	}
+
+	return ensure_verity_info(inode);
+}
+EXPORT_SYMBOL_GPL(fsverity_file_open);
+
+/**
+ * fsverity_cleanup_inode - free the inode's verity info, if present
+ *
+ * Filesystems must call this on inode eviction to free ->i_verity_info.
+ */
+void fsverity_cleanup_inode(struct inode *inode)
+{
+	fsverity_free_info(inode->i_verity_info);
+	inode->i_verity_info = NULL;
+}
+EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
+
+int __init fsverity_init_info_cache(void)
+{
+	fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
+						   SLAB_RECLAIM_ACCOUNT,
+						   measurement);
+	if (!fsverity_info_cachep)
+		return -ENOMEM;
+	return 0;
+}
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
new file mode 100644
index 00000000000000..1372c236c8770c
--- /dev/null
+++ b/include/linux/fsverity.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * fs-verity: read-only file-based authenticity protection
+ *
+ * This header declares the interface between the fs/verity/ support layer and
+ * filesystems that support fs-verity.
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#ifndef _LINUX_FSVERITY_H
+#define _LINUX_FSVERITY_H
+
+#include <linux/fs.h>
+#include <uapi/linux/fsverity.h>
+
+/* Verity operations for filesystems */
+struct fsverity_operations {
+
+	/**
+	 * Get the verity descriptor of the given inode.
+	 *
+	 * @inode: an inode with the S_VERITY flag set
+	 * @buf: buffer in which to place the verity descriptor
+	 * @bufsize: size of @buf, or 0 to retrieve the size only
+	 *
+	 * If bufsize == 0, then the size of the verity descriptor is returned.
+	 * Otherwise the verity descriptor is written to 'buf' and its actual
+	 * size is returned; -ERANGE is returned if it's too large.  This may be
+	 * called by multiple processes concurrently on the same inode.
+	 *
+	 * Return: the size on success, -errno on failure
+	 */
+	int (*get_verity_descriptor)(struct inode *inode, void *buf,
+				     size_t bufsize);
+};
+
+#ifdef CONFIG_FS_VERITY
+
+static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
+{
+	/* pairs with the cmpxchg_release() in fsverity_set_info() */
+	return READ_ONCE(inode->i_verity_info);
+}
+
+/* open.c */
+
+extern int fsverity_file_open(struct inode *inode, struct file *filp);
+extern void fsverity_cleanup_inode(struct inode *inode);
+
+#else /* !CONFIG_FS_VERITY */
+
+static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
+{
+	return NULL;
+}
+
+/* open.c */
+
+static inline int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+	return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
+}
+
+static inline void fsverity_cleanup_inode(struct inode *inode)
+{
+}
+
+#endif	/* !CONFIG_FS_VERITY */
+
+#endif	/* _LINUX_FSVERITY_H */
