fs/verity/hash_algs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/verity/hash_algs.c: fs-verity hash algorithms
   4  *
   5  * Copyright 2019 Google LLC
   6  */
   7
   8 #include "fsverity_private.h"
   9
  10 #include <crypto/hash.h>
  11 #include <linux/scatterlist.h>
  12
  13 /* The hash algorithms supported by fs-verity */
  14 struct fsverity_hash_alg fsverity_hash_algs[] = {
  15         [FS_VERITY_HASH_ALG_SHA256] = {
  16                 .name = "sha256",
  17                 .digest_size = SHA256_DIGEST_SIZE,
  18                 .block_size = SHA256_BLOCK_SIZE,
  19         },
  20         [FS_VERITY_HASH_ALG_SHA512] = {
  21                 .name = "sha512",
  22                 .digest_size = SHA512_DIGEST_SIZE,
  23                 .block_size = SHA512_BLOCK_SIZE,
  24         },
  25 };
  26
  27 /**
  28  * fsverity_get_hash_alg() - validate and prepare a hash algorithm
  29  * @inode: optional inode for logging purposes
  30  * @num: the hash algorithm number
  31  *
  32  * Get the struct fsverity_hash_alg for the given hash algorithm number, and
  33  * ensure it has a hash transform ready to go.  The hash transforms are
  34  * allocated on-demand so that we don't waste resources unnecessarily, and
  35  * because the crypto modules may be initialized later than fs/verity/.
  36  *
  37  * Return: pointer to the hash alg on success, else an ERR_PTR()
  38  */
  39 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
  40                                                       unsigned int num)
  41 {
  42         struct fsverity_hash_alg *alg;
  43         struct crypto_ahash *tfm;
  44         int err;
  45
  46         if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
  47             !fsverity_hash_algs[num].name) {
  48                 fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
  49                 return ERR_PTR(-EINVAL);
  50         }
  51         alg = &fsverity_hash_algs[num];
  52
  53         /* pairs with cmpxchg() below */
  54         tfm = READ_ONCE(alg->tfm);
  55         if (likely(tfm != NULL))
  56                 return alg;
  57         /*
  58          * Using the shash API would make things a bit simpler, but the ahash
  59          * API is preferable as it allows the use of crypto accelerators.
  60          */
  61         tfm = crypto_alloc_ahash(alg->name, 0, 0);
  62         if (IS_ERR(tfm)) {
  63                 if (PTR_ERR(tfm) == -ENOENT) {
  64                         fsverity_warn(inode,
  65                                       "Missing crypto API support for hash algorithm \"%s\"",
  66                                       alg->name);
  67                         return ERR_PTR(-ENOPKG);
  68                 }
  69                 fsverity_err(inode,
  70                              "Error allocating hash algorithm \"%s\": %ld",
  71                              alg->name, PTR_ERR(tfm));
  72                 return ERR_CAST(tfm);
  73         }
  74
  75         err = -EINVAL;
  76         if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
  77                 goto err_free_tfm;
  78         if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
  79                 goto err_free_tfm;
  80
  81         pr_info("%s using implementation \"%s\"\n",
  82                 alg->name, crypto_ahash_driver_name(tfm));
  83
  84         /* pairs with READ_ONCE() above */
  85         if (cmpxchg(&alg->tfm, NULL, tfm) != NULL)
  86                 crypto_free_ahash(tfm);
  87
  88         return alg;
  89
  90 err_free_tfm:
  91         crypto_free_ahash(tfm);
  92         return ERR_PTR(err);
  93 }
  94
  95 /**
  96  * fsverity_prepare_hash_state() - precompute the initial hash state
  97  * @alg: hash algorithm
  98  * @salt: a salt which is to be prepended to all data to be hashed
  99  * @salt_size: salt size in bytes, possibly 0
 100  *
 101  * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
 102  *         initial hash state on success or an ERR_PTR() on failure.
 103  */
 104 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
 105                                       const u8 *salt, size_t salt_size)
 106 {
 107         u8 *hashstate = NULL;
 108         struct ahash_request *req = NULL;
 109         u8 *padded_salt = NULL;
 110         size_t padded_salt_size;
 111         struct scatterlist sg;
 112         DECLARE_CRYPTO_WAIT(wait);
 113         int err;
 114
 115         if (salt_size == 0)
 116                 return NULL;
 117
 118         hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
 119         if (!hashstate)
 120                 return ERR_PTR(-ENOMEM);
 121
 122         req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
 123         if (!req) {
 124                 err = -ENOMEM;
 125                 goto err_free;
 126         }
 127
 128         /*
 129          * Zero-pad the salt to the next multiple of the input size of the hash
 130          * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
 131          * bytes for SHA-512.  This ensures that the hash algorithm won't have
 132          * any bytes buffered internally after processing the salt, thus making
 133          * salted hashing just as fast as unsalted hashing.
 134          */
 135         padded_salt_size = round_up(salt_size, alg->block_size);
 136         padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
 137         if (!padded_salt) {
 138                 err = -ENOMEM;
 139                 goto err_free;
 140         }
 141         memcpy(padded_salt, salt, salt_size);
 142
 143         sg_init_one(&sg, padded_salt, padded_salt_size);
 144         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
 145                                         CRYPTO_TFM_REQ_MAY_BACKLOG,
 146                                    crypto_req_done, &wait);
 147         ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);
 148
 149         err = crypto_wait_req(crypto_ahash_init(req), &wait);
 150         if (err)
 151                 goto err_free;
 152
 153         err = crypto_wait_req(crypto_ahash_update(req), &wait);
 154         if (err)
 155                 goto err_free;
 156
 157         err = crypto_ahash_export(req, hashstate);
 158         if (err)
 159                 goto err_free;
 160 out:
 161         ahash_request_free(req);
 162         kfree(padded_salt);
 163         return hashstate;
 164
 165 err_free:
 166         kfree(hashstate);
 167         hashstate = ERR_PTR(err);
 168         goto out;
 169 }
 170
 171 /**
 172  * fsverity_hash_page() - hash a single data or hash page
 173  * @params: the Merkle tree's parameters
 174  * @inode: inode for which the hashing is being done
 175  * @req: preallocated hash request
 176  * @page: the page to hash
 177  * @out: output digest, size 'params->digest_size' bytes
 178  *
 179  * Hash a single data or hash block, assuming block_size == PAGE_SIZE.
 180  * The hash is salted if a salt is specified in the Merkle tree parameters.
 181  *
 182  * Return: 0 on success, -errno on failure
 183  */
 184 int fsverity_hash_page(const struct merkle_tree_params *params,
 185                        const struct inode *inode,
 186                        struct ahash_request *req, struct page *page, u8 *out)
 187 {
 188         struct scatterlist sg;
 189         DECLARE_CRYPTO_WAIT(wait);
 190         int err;
 191
 192         if (WARN_ON(params->block_size != PAGE_SIZE))
 193                 return -EINVAL;
 194
 195         sg_init_table(&sg, 1);
 196         sg_set_page(&sg, page, PAGE_SIZE, 0);
 197         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
 198                                         CRYPTO_TFM_REQ_MAY_BACKLOG,
 199                                    crypto_req_done, &wait);
 200         ahash_request_set_crypt(req, &sg, out, PAGE_SIZE);
 201
 202         if (params->hashstate) {
 203                 err = crypto_ahash_import(req, params->hashstate);
 204                 if (err) {
 205                         fsverity_err(inode,
 206                                      "Error %d importing hash state", err);
 207                         return err;
 208                 }
 209                 err = crypto_ahash_finup(req);
 210         } else {
 211                 err = crypto_ahash_digest(req);
 212         }
 213
 214         err = crypto_wait_req(err, &wait);
 215         if (err)
 216                 fsverity_err(inode, "Error %d computing page hash", err);
 217         return err;
 218 }
 219
 220 /**
 221  * fsverity_hash_buffer() - hash some data
 222  * @alg: the hash algorithm to use
 223  * @data: the data to hash
 224  * @size: size of data to hash, in bytes
 225  * @out: output digest, size 'alg->digest_size' bytes
 226  *
 227  * Hash some data which is located in physically contiguous memory (i.e. memory
 228  * allocated by kmalloc(), not by vmalloc()).  No salt is used.
 229  *
 230  * Return: 0 on success, -errno on failure
 231  */
 232 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
 233                          const void *data, size_t size, u8 *out)
 234 {
 235         struct ahash_request *req;
 236         struct scatterlist sg;
 237         DECLARE_CRYPTO_WAIT(wait);
 238         int err;
 239
 240         req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
 241         if (!req)
 242                 return -ENOMEM;
 243
 244         sg_init_one(&sg, data, size);
 245         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
 246                                         CRYPTO_TFM_REQ_MAY_BACKLOG,
 247                                    crypto_req_done, &wait);
 248         ahash_request_set_crypt(req, &sg, out, size);
 249
 250         err = crypto_wait_req(crypto_ahash_digest(req), &wait);
 251
 252         ahash_request_free(req);
 253         return err;
 254 }
 255
 256 void __init fsverity_check_hash_algs(void)
 257 {
 258         size_t i;
 259
 260         /*
 261          * Sanity check the hash algorithms (could be a build-time check, but
 262          * they're in an array)
 263          */
 264         for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
 265                 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
 266
 267                 if (!alg->name)
 268                         continue;
 269
 270                 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
 271
 272                 /*
 273                  * For efficiency, the implementation currently assumes the
 274                  * digest and block sizes are powers of 2.  This limitation can
 275                  * be lifted if the code is updated to handle other values.
 276                  */
 277                 BUG_ON(!is_power_of_2(alg->digest_size));
 278                 BUG_ON(!is_power_of_2(alg->block_size));
 279         }
 280 }