fs/verity/fsverity_private.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * fs-verity: read-only file-based authenticity protection
   4  *
   5  * Copyright 2019 Google LLC
   6  */
   7
   8 #ifndef _FSVERITY_PRIVATE_H
   9 #define _FSVERITY_PRIVATE_H
  10
  11 #ifdef CONFIG_FS_VERITY_DEBUG
  12 #define DEBUG
  13 #endif
  14
  15 #define pr_fmt(fmt) "fs-verity: " fmt
  16
  17 #include <crypto/sha.h>
  18 #include <linux/fsverity.h>
  19 #include <linux/mempool.h>
  20
  21 struct ahash_request;
  22
  23 /*
  24  * Implementation limit: maximum depth of the Merkle tree.  For now 8 is plenty;
  25  * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
  26  */
  27 #define FS_VERITY_MAX_LEVELS            8
  28
  29 /*
  30  * Largest digest size among all hash algorithms supported by fs-verity.
  31  * Currently assumed to be <= size of fsverity_descriptor::root_hash.
  32  */
  33 #define FS_VERITY_MAX_DIGEST_SIZE       SHA512_DIGEST_SIZE
  34
  35 /* A hash algorithm supported by fs-verity */
  36 struct fsverity_hash_alg {
  37         struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
  38         const char *name;         /* crypto API name, e.g. sha256 */
  39         unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
  40         unsigned int block_size;  /* block size in bytes, e.g. 64 for SHA-256 */
  41         mempool_t req_pool;       /* mempool with a preallocated hash request */
  42 };
  43
  44 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */
  45 struct merkle_tree_params {
  46         struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
  47         const u8 *hashstate;            /* initial hash state or NULL */
  48         unsigned int digest_size;       /* same as hash_alg->digest_size */
  49         unsigned int block_size;        /* size of data and tree blocks */
  50         unsigned int hashes_per_block;  /* number of hashes per tree block */
  51         unsigned int log_blocksize;     /* log2(block_size) */
  52         unsigned int log_arity;         /* log2(hashes_per_block) */
  53         unsigned int num_levels;        /* number of levels in Merkle tree */
  54         u64 tree_size;                  /* Merkle tree size in bytes */
  55         unsigned long level0_blocks;    /* number of blocks in tree level 0 */
  56
  57         /*
  58          * Starting block index for each tree level, ordered from leaf level (0)
  59          * to root level ('num_levels - 1')
  60          */
  61         u64 level_start[FS_VERITY_MAX_LEVELS];
  62 };
  63
  64 /*
  65  * fsverity_info - cached verity metadata for an inode
  66  *
  67  * When a verity file is first opened, an instance of this struct is allocated
  68  * and stored in ->i_verity_info; it remains until the inode is evicted.  It
  69  * caches information about the Merkle tree that's needed to efficiently verify
  70  * data read from the file.  It also caches the file measurement.  The Merkle
  71  * tree pages themselves are not cached here, but the filesystem may cache them.
  72  */
  73 struct fsverity_info {
  74         struct merkle_tree_params tree_params;
  75         u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
  76         u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
  77         const struct inode *inode;
  78 };
  79
  80 /*
  81  * Merkle tree properties.  The file measurement is the hash of this structure
  82  * excluding the signature and with the sig_size field set to 0.
  83  */
  84 struct fsverity_descriptor {
  85         __u8 version;           /* must be 1 */
  86         __u8 hash_algorithm;    /* Merkle tree hash algorithm */
  87         __u8 log_blocksize;     /* log2 of size of data and tree blocks */
  88         __u8 salt_size;         /* size of salt in bytes; 0 if none */
  89         __le32 sig_size;        /* size of signature in bytes; 0 if none */
  90         __le64 data_size;       /* size of file the Merkle tree is built over */
  91         __u8 root_hash[64];     /* Merkle tree root hash */
  92         __u8 salt[32];          /* salt prepended to each hashed block */
  93         __u8 __reserved[144];   /* must be 0's */
  94         __u8 signature[];       /* optional PKCS#7 signature */
  95 };
  96
  97 /* Arbitrary limit to bound the kmalloc() size.  Can be changed. */
  98 #define FS_VERITY_MAX_DESCRIPTOR_SIZE   16384
  99
 100 #define FS_VERITY_MAX_SIGNATURE_SIZE    (FS_VERITY_MAX_DESCRIPTOR_SIZE - \
 101                                          sizeof(struct fsverity_descriptor))
 102
 103 /*
 104  * Format in which verity file measurements are signed.  This is the same as
 105  * 'struct fsverity_digest', except here some magic bytes are prepended to
 106  * provide some context about what is being signed in case the same key is used
 107  * for non-fsverity purposes, and here the fields have fixed endianness.
 108  */
 109 struct fsverity_signed_digest {
 110         char magic[8];                  /* must be "FSVerity" */
 111         __le16 digest_algorithm;
 112         __le16 digest_size;
 113         __u8 digest[];
 114 };
 115
 116 /* hash_algs.c */
 117
 118 extern struct fsverity_hash_alg fsverity_hash_algs[];
 119
 120 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
 121                                                 unsigned int num);
 122 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
 123                                                   gfp_t gfp_flags);
 124 void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
 125                                 struct ahash_request *req);
 126 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
 127                                       const u8 *salt, size_t salt_size);
 128 int fsverity_hash_page(const struct merkle_tree_params *params,
 129                        const struct inode *inode,
 130                        struct ahash_request *req, struct page *page, u8 *out);
 131 int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
 132                          const void *data, size_t size, u8 *out);
 133 void __init fsverity_check_hash_algs(void);
 134
 135 /* init.c */
 136
 137 void __printf(3, 4) __cold
 138 fsverity_msg(const struct inode *inode, const char *level,
 139              const char *fmt, ...);
 140
 141 #define fsverity_warn(inode, fmt, ...)          \
 142         fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
 143 #define fsverity_err(inode, fmt, ...)           \
 144         fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
 145
 146 /* open.c */
 147
 148 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
 149                                      const struct inode *inode,
 150                                      unsigned int hash_algorithm,
 151                                      unsigned int log_blocksize,
 152                                      const u8 *salt, size_t salt_size);
 153
 154 struct fsverity_info *fsverity_create_info(const struct inode *inode,
 155                                            void *desc, size_t desc_size);
 156
 157 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
 158
 159 void fsverity_free_info(struct fsverity_info *vi);
 160
 161 int __init fsverity_init_info_cache(void);
 162 void __init fsverity_exit_info_cache(void);
 163
 164 /* signature.c */
 165
 166 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
 167 int fsverity_verify_signature(const struct fsverity_info *vi,
 168                               const struct fsverity_descriptor *desc,
 169                               size_t desc_size);
 170
 171 int __init fsverity_init_signature(void);
 172 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
 173 static inline int
 174 fsverity_verify_signature(const struct fsverity_info *vi,
 175                           const struct fsverity_descriptor *desc,
 176                           size_t desc_size)
 177 {
 178         return 0;
 179 }
 180
 181 static inline int fsverity_init_signature(void)
 182 {
 183         return 0;
 184 }
 185 #endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
 186
 187 /* verify.c */
 188
 189 int __init fsverity_init_workqueue(void);
 190 void __init fsverity_exit_workqueue(void);
 191
 192 #endif /* _FSVERITY_PRIVATE_H */