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/* 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 <linux/mm.h>
#include <crypto/hash_info.h>
#include <crypto/sha2.h>
#include <uapi/linux/fsverity.h>
/*
* Largest digest size among all hash algorithms supported by fs-verity.
* Currently assumed to be <= size of fsverity_descriptor::root_hash.
*/
#define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
/* Arbitrary limit to bound the kmalloc() size. Can be changed. */
#define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384
/* Verity operations for filesystems */
struct fsverity_operations {
/**
* Begin enabling verity on the given file.
*
* @filp: a readonly file descriptor for the file
*
* The filesystem must do any needed filesystem-specific preparations
* for enabling verity, e.g. evicting inline data. It also must return
* -EBUSY if verity is already being enabled on the given file.
*
* i_rwsem is held for write.
*
* Return: 0 on success, -errno on failure
*/
int (*begin_enable_verity)(struct file *filp);
/**
* End enabling verity on the given file.
*
* @filp: a readonly file descriptor for the file
* @desc: the verity descriptor to write, or NULL on failure
* @desc_size: size of verity descriptor, or 0 on failure
* @merkle_tree_size: total bytes the Merkle tree took up
*
* If desc == NULL, then enabling verity failed and the filesystem only
* must do any necessary cleanups. Else, it must also store the given
* verity descriptor to a fs-specific location associated with the inode
* and do any fs-specific actions needed to mark the inode as a verity
* inode, e.g. setting a bit in the on-disk inode. The filesystem is
* also responsible for setting the S_VERITY flag in the VFS inode.
*
* i_rwsem is held for write, but it may have been dropped between
* ->begin_enable_verity() and ->end_enable_verity().
*
* Return: 0 on success, -errno on failure
*/
int (*end_enable_verity)(struct file *filp, const void *desc,
size_t desc_size, u64 merkle_tree_size);
/**
* 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);
/**
* Read a Merkle tree page of the given inode.
*
* @inode: the inode
* @index: 0-based index of the page within the Merkle tree
* @num_ra_pages: The number of Merkle tree pages that should be
* prefetched starting at @index if the page at @index
* isn't already cached. Implementations may ignore this
* argument; it's only a performance optimization.
*
* This can be called at any time on an open verity file. It may be
* called by multiple processes concurrently, even with the same page.
*
* Note that this must retrieve a *page*, not necessarily a *block*.
*
* Return: the page on success, ERR_PTR() on failure
*/
struct page *(*read_merkle_tree_page)(struct inode *inode,
pgoff_t index,
unsigned long num_ra_pages);
/**
* Write a Merkle tree block to the given inode.
*
* @inode: the inode for which the Merkle tree is being built
* @buf: the Merkle tree block to write
* @pos: the position of the block in the Merkle tree (in bytes)
* @size: the Merkle tree block size (in bytes)
*
* This is only called between ->begin_enable_verity() and
* ->end_enable_verity().
*
* Return: 0 on success, -errno on failure
*/
int (*write_merkle_tree_block)(struct inode *inode, const void *buf,
u64 pos, unsigned int size);
};
#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().
* I.e., another task may publish ->i_verity_info concurrently,
* executing a RELEASE barrier. We need to use smp_load_acquire() here
* to safely ACQUIRE the memory the other task published.
*/
return smp_load_acquire(&inode->i_verity_info);
}
/* enable.c */
int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
/* measure.c */
int fsverity_ioctl_measure(struct file *filp, void __user *arg);
int fsverity_get_digest(struct inode *inode,
u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
u8 *alg, enum hash_algo *halg);
/* open.c */
int __fsverity_file_open(struct inode *inode, struct file *filp);
int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
void __fsverity_cleanup_inode(struct inode *inode);
/**
* fsverity_cleanup_inode() - free the inode's verity info, if present
* @inode: an inode being evicted
*
* Filesystems must call this on inode eviction to free ->i_verity_info.
*/
static inline void fsverity_cleanup_inode(struct inode *inode)
{
if (inode->i_verity_info)
__fsverity_cleanup_inode(inode);
}
/* read_metadata.c */
int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg);
/* verify.c */
bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset);
void fsverity_verify_bio(struct bio *bio);
void fsverity_enqueue_verify_work(struct work_struct *work);
#else /* !CONFIG_FS_VERITY */
static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
{
return NULL;
}
/* enable.c */
static inline int fsverity_ioctl_enable(struct file *filp,
const void __user *arg)
{
return -EOPNOTSUPP;
}
/* measure.c */
static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg)
{
return -EOPNOTSUPP;
}
static inline int fsverity_get_digest(struct inode *inode,
u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
u8 *alg, enum hash_algo *halg)
{
/*
* fsverity is not enabled in the kernel configuration, so always report
* that the file doesn't have fsverity enabled (digest size 0).
*/
return 0;
}
/* open.c */
static inline int __fsverity_file_open(struct inode *inode, struct file *filp)
{
return -EOPNOTSUPP;
}
static inline int __fsverity_prepare_setattr(struct dentry *dentry,
struct iattr *attr)
{
return -EOPNOTSUPP;
}
static inline void fsverity_cleanup_inode(struct inode *inode)
{
}
/* read_metadata.c */
static inline int fsverity_ioctl_read_metadata(struct file *filp,
const void __user *uarg)
{
return -EOPNOTSUPP;
}
/* verify.c */
static inline bool fsverity_verify_blocks(struct folio *folio, size_t len,
size_t offset)
{
WARN_ON_ONCE(1);
return false;
}
static inline void fsverity_verify_bio(struct bio *bio)
{
WARN_ON_ONCE(1);
}
static inline void fsverity_enqueue_verify_work(struct work_struct *work)
{
WARN_ON_ONCE(1);
}
#endif /* !CONFIG_FS_VERITY */
static inline bool fsverity_verify_folio(struct folio *folio)
{
return fsverity_verify_blocks(folio, folio_size(folio), 0);
}
static inline bool fsverity_verify_page(struct page *page)
{
return fsverity_verify_blocks(page_folio(page), PAGE_SIZE, 0);
}
/**
* fsverity_active() - do reads from the inode need to go through fs-verity?
* @inode: inode to check
*
* This checks whether ->i_verity_info has been set.
*
* Filesystems call this from ->readahead() to check whether the pages need to
* be verified or not. Don't use IS_VERITY() for this purpose; it's subject to
* a race condition where the file is being read concurrently with
* FS_IOC_ENABLE_VERITY completing. (S_VERITY is set before ->i_verity_info.)
*
* Return: true if reads need to go through fs-verity, otherwise false
*/
static inline bool fsverity_active(const struct inode *inode)
{
return fsverity_get_info(inode) != NULL;
}
/**
* 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
*/
static inline int fsverity_file_open(struct inode *inode, struct file *filp)
{
if (IS_VERITY(inode))
return __fsverity_file_open(inode, filp);
return 0;
}
/**
* fsverity_prepare_setattr() - prepare to change a verity inode's attributes
* @dentry: dentry through which the inode is being changed
* @attr: attributes to change
*
* Verity files are immutable, so deny truncates. This isn't covered by the
* open-time check because sys_truncate() takes a path, not a file descriptor.
*
* Return: 0 on success, -errno on failure
*/
static inline int fsverity_prepare_setattr(struct dentry *dentry,
struct iattr *attr)
{
if (IS_VERITY(d_inode(dentry)))
return __fsverity_prepare_setattr(dentry, attr);
return 0;
}
#endif /* _LINUX_FSVERITY_H */