include/linux/fsverity.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * fs-verity: read-only file-based authenticity protection
   4  *
   5  * This header declares the interface between the fs/verity/ support layer and
   6  * filesystems that support fs-verity.
   7  *
   8  * Copyright 2019 Google LLC
   9  */
  10
  11 #ifndef _LINUX_FSVERITY_H
  12 #define _LINUX_FSVERITY_H
  13
  14 #include <linux/fs.h>
  15 #include <uapi/linux/fsverity.h>
  16
  17 /* Verity operations for filesystems */
  18 struct fsverity_operations {
  19
  20         /**
  21          * Begin enabling verity on the given file.
  22          *
  23          * @filp: a readonly file descriptor for the file
  24          *
  25          * The filesystem must do any needed filesystem-specific preparations
  26          * for enabling verity, e.g. evicting inline data.  It also must return
  27          * -EBUSY if verity is already being enabled on the given file.
  28          *
  29          * i_rwsem is held for write.
  30          *
  31          * Return: 0 on success, -errno on failure
  32          */
  33         int (*begin_enable_verity)(struct file *filp);
  34
  35         /**
  36          * End enabling verity on the given file.
  37          *
  38          * @filp: a readonly file descriptor for the file
  39          * @desc: the verity descriptor to write, or NULL on failure
  40          * @desc_size: size of verity descriptor, or 0 on failure
  41          * @merkle_tree_size: total bytes the Merkle tree took up
  42          *
  43          * If desc == NULL, then enabling verity failed and the filesystem only
  44          * must do any necessary cleanups.  Else, it must also store the given
  45          * verity descriptor to a fs-specific location associated with the inode
  46          * and do any fs-specific actions needed to mark the inode as a verity
  47          * inode, e.g. setting a bit in the on-disk inode.  The filesystem is
  48          * also responsible for setting the S_VERITY flag in the VFS inode.
  49          *
  50          * i_rwsem is held for write, but it may have been dropped between
  51          * ->begin_enable_verity() and ->end_enable_verity().
  52          *
  53          * Return: 0 on success, -errno on failure
  54          */
  55         int (*end_enable_verity)(struct file *filp, const void *desc,
  56                                  size_t desc_size, u64 merkle_tree_size);
  57
  58         /**
  59          * Get the verity descriptor of the given inode.
  60          *
  61          * @inode: an inode with the S_VERITY flag set
  62          * @buf: buffer in which to place the verity descriptor
  63          * @bufsize: size of @buf, or 0 to retrieve the size only
  64          *
  65          * If bufsize == 0, then the size of the verity descriptor is returned.
  66          * Otherwise the verity descriptor is written to 'buf' and its actual
  67          * size is returned; -ERANGE is returned if it's too large.  This may be
  68          * called by multiple processes concurrently on the same inode.
  69          *
  70          * Return: the size on success, -errno on failure
  71          */
  72         int (*get_verity_descriptor)(struct inode *inode, void *buf,
  73                                      size_t bufsize);
  74
  75         /**
  76          * Read a Merkle tree page of the given inode.
  77          *
  78          * @inode: the inode
  79          * @index: 0-based index of the page within the Merkle tree
  80          * @num_ra_pages: The number of Merkle tree pages that should be
  81          *                prefetched starting at @index if the page at @index
  82          *                isn't already cached.  Implementations may ignore this
  83          *                argument; it's only a performance optimization.
  84          *
  85          * This can be called at any time on an open verity file, as well as
  86          * between ->begin_enable_verity() and ->end_enable_verity().  It may be
  87          * called by multiple processes concurrently, even with the same page.
  88          *
  89          * Note that this must retrieve a *page*, not necessarily a *block*.
  90          *
  91          * Return: the page on success, ERR_PTR() on failure
  92          */
  93         struct page *(*read_merkle_tree_page)(struct inode *inode,
  94                                               pgoff_t index,
  95                                               unsigned long num_ra_pages);
  96
  97         /**
  98          * Write a Merkle tree block to the given inode.
  99          *
 100          * @inode: the inode for which the Merkle tree is being built
 101          * @buf: block to write
 102          * @index: 0-based index of the block within the Merkle tree
 103          * @log_blocksize: log base 2 of the Merkle tree block size
 104          *
 105          * This is only called between ->begin_enable_verity() and
 106          * ->end_enable_verity().
 107          *
 108          * Return: 0 on success, -errno on failure
 109          */
 110         int (*write_merkle_tree_block)(struct inode *inode, const void *buf,
 111                                        u64 index, int log_blocksize);
 112 };
 113
 114 #ifdef CONFIG_FS_VERITY
 115
 116 static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
 117 {
 118         /*
 119          * Pairs with the cmpxchg_release() in fsverity_set_info().
 120          * I.e., another task may publish ->i_verity_info concurrently,
 121          * executing a RELEASE barrier.  We need to use smp_load_acquire() here
 122          * to safely ACQUIRE the memory the other task published.
 123          */
 124         return smp_load_acquire(&inode->i_verity_info);
 125 }
 126
 127 /* enable.c */
 128
 129 int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
 130
 131 /* measure.c */
 132
 133 int fsverity_ioctl_measure(struct file *filp, void __user *arg);
 134
 135 /* open.c */
 136
 137 int fsverity_file_open(struct inode *inode, struct file *filp);
 138 int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 139 void fsverity_cleanup_inode(struct inode *inode);
 140
 141 /* read_metadata.c */
 142
 143 int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg);
 144
 145 /* verify.c */
 146
 147 bool fsverity_verify_page(struct page *page);
 148 void fsverity_verify_bio(struct bio *bio);
 149 void fsverity_enqueue_verify_work(struct work_struct *work);
 150
 151 #else /* !CONFIG_FS_VERITY */
 152
 153 static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
 154 {
 155         return NULL;
 156 }
 157
 158 /* enable.c */
 159
 160 static inline int fsverity_ioctl_enable(struct file *filp,
 161                                         const void __user *arg)
 162 {
 163         return -EOPNOTSUPP;
 164 }
 165
 166 /* measure.c */
 167
 168 static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg)
 169 {
 170         return -EOPNOTSUPP;
 171 }
 172
 173 /* open.c */
 174
 175 static inline int fsverity_file_open(struct inode *inode, struct file *filp)
 176 {
 177         return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
 178 }
 179
 180 static inline int fsverity_prepare_setattr(struct dentry *dentry,
 181                                            struct iattr *attr)
 182 {
 183         return IS_VERITY(d_inode(dentry)) ? -EOPNOTSUPP : 0;
 184 }
 185
 186 static inline void fsverity_cleanup_inode(struct inode *inode)
 187 {
 188 }
 189
 190 /* read_metadata.c */
 191
 192 static inline int fsverity_ioctl_read_metadata(struct file *filp,
 193                                                const void __user *uarg)
 194 {
 195         return -EOPNOTSUPP;
 196 }
 197
 198 /* verify.c */
 199
 200 static inline bool fsverity_verify_page(struct page *page)
 201 {
 202         WARN_ON(1);
 203         return false;
 204 }
 205
 206 static inline void fsverity_verify_bio(struct bio *bio)
 207 {
 208         WARN_ON(1);
 209 }
 210
 211 static inline void fsverity_enqueue_verify_work(struct work_struct *work)
 212 {
 213         WARN_ON(1);
 214 }
 215
 216 #endif  /* !CONFIG_FS_VERITY */
 217
 218 /**
 219  * fsverity_active() - do reads from the inode need to go through fs-verity?
 220  * @inode: inode to check
 221  *
 222  * This checks whether ->i_verity_info has been set.
 223  *
 224  * Filesystems call this from ->readpages() to check whether the pages need to
 225  * be verified or not.  Don't use IS_VERITY() for this purpose; it's subject to
 226  * a race condition where the file is being read concurrently with
 227  * FS_IOC_ENABLE_VERITY completing.  (S_VERITY is set before ->i_verity_info.)
 228  *
 229  * Return: true if reads need to go through fs-verity, otherwise false
 230  */
 231 static inline bool fsverity_active(const struct inode *inode)
 232 {
 233         return fsverity_get_info(inode) != NULL;
 234 }
 235
 236 #endif  /* _LINUX_FSVERITY_H */