linux/fs/crypto/inline_crypt.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Inline encryption support for fscrypt
   4 *
   5 * Copyright 2019 Google LLC
   6 */
   7
   8/*
   9 * With "inline encryption", the block layer handles the decryption/encryption
  10 * as part of the bio, instead of the filesystem doing the crypto itself via
  11 * crypto API.  See Documentation/block/inline-encryption.rst.  fscrypt still
  12 * provides the key and IV to use.
  13 */
  14
  15#include <linux/blk-crypto.h>
  16#include <linux/blkdev.h>
  17#include <linux/buffer_head.h>
  18#include <linux/sched/mm.h>
  19#include <linux/slab.h>
  20
  21#include "fscrypt_private.h"
  22
  23struct fscrypt_blk_crypto_key {
  24        struct blk_crypto_key base;
  25        int num_devs;
  26        struct request_queue *devs[];
  27};
  28
  29static int fscrypt_get_num_devices(struct super_block *sb)
  30{
  31        if (sb->s_cop->get_num_devices)
  32                return sb->s_cop->get_num_devices(sb);
  33        return 1;
  34}
  35
  36static void fscrypt_get_devices(struct super_block *sb, int num_devs,
  37                                struct request_queue **devs)
  38{
  39        if (num_devs == 1)
  40                devs[0] = bdev_get_queue(sb->s_bdev);
  41        else
  42                sb->s_cop->get_devices(sb, devs);
  43}
  44
  45static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci)
  46{
  47        struct super_block *sb = ci->ci_inode->i_sb;
  48        unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
  49        int ino_bits = 64, lblk_bits = 64;
  50
  51        if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
  52                return offsetofend(union fscrypt_iv, nonce);
  53
  54        if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
  55                return sizeof(__le64);
  56
  57        if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
  58                return sizeof(__le32);
  59
  60        /* Default case: IVs are just the file logical block number */
  61        if (sb->s_cop->get_ino_and_lblk_bits)
  62                sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
  63        return DIV_ROUND_UP(lblk_bits, 8);
  64}
  65
  66/* Enable inline encryption for this file if supported. */
  67int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
  68{
  69        const struct inode *inode = ci->ci_inode;
  70        struct super_block *sb = inode->i_sb;
  71        struct blk_crypto_config crypto_cfg;
  72        int num_devs;
  73        struct request_queue **devs;
  74        int i;
  75
  76        /* The file must need contents encryption, not filenames encryption */
  77        if (!S_ISREG(inode->i_mode))
  78                return 0;
  79
  80        /* The crypto mode must have a blk-crypto counterpart */
  81        if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
  82                return 0;
  83
  84        /* The filesystem must be mounted with -o inlinecrypt */
  85        if (!(sb->s_flags & SB_INLINECRYPT))
  86                return 0;
  87
  88        /*
  89         * When a page contains multiple logically contiguous filesystem blocks,
  90         * some filesystem code only calls fscrypt_mergeable_bio() for the first
  91         * block in the page. This is fine for most of fscrypt's IV generation
  92         * strategies, where contiguous blocks imply contiguous IVs. But it
  93         * doesn't work with IV_INO_LBLK_32. For now, simply exclude
  94         * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
  95         */
  96        if ((fscrypt_policy_flags(&ci->ci_policy) &
  97             FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
  98            sb->s_blocksize != PAGE_SIZE)
  99                return 0;
 100
 101        /*
 102         * On all the filesystem's devices, blk-crypto must support the crypto
 103         * configuration that the file would use.
 104         */
 105        crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
 106        crypto_cfg.data_unit_size = sb->s_blocksize;
 107        crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
 108        num_devs = fscrypt_get_num_devices(sb);
 109        devs = kmalloc_array(num_devs, sizeof(*devs), GFP_KERNEL);
 110        if (!devs)
 111                return -ENOMEM;
 112        fscrypt_get_devices(sb, num_devs, devs);
 113
 114        for (i = 0; i < num_devs; i++) {
 115                if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
 116                        goto out_free_devs;
 117        }
 118
 119        ci->ci_inlinecrypt = true;
 120out_free_devs:
 121        kfree(devs);
 122
 123        return 0;
 124}
 125
 126int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
 127                                     const u8 *raw_key,
 128                                     const struct fscrypt_info *ci)
 129{
 130        const struct inode *inode = ci->ci_inode;
 131        struct super_block *sb = inode->i_sb;
 132        enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
 133        int num_devs = fscrypt_get_num_devices(sb);
 134        int queue_refs = 0;
 135        struct fscrypt_blk_crypto_key *blk_key;
 136        int err;
 137        int i;
 138
 139        blk_key = kzalloc(struct_size(blk_key, devs, num_devs), GFP_KERNEL);
 140        if (!blk_key)
 141                return -ENOMEM;
 142
 143        blk_key->num_devs = num_devs;
 144        fscrypt_get_devices(sb, num_devs, blk_key->devs);
 145
 146        err = blk_crypto_init_key(&blk_key->base, raw_key, crypto_mode,
 147                                  fscrypt_get_dun_bytes(ci), sb->s_blocksize);
 148        if (err) {
 149                fscrypt_err(inode, "error %d initializing blk-crypto key", err);
 150                goto fail;
 151        }
 152
 153        /*
 154         * We have to start using blk-crypto on all the filesystem's devices.
 155         * We also have to save all the request_queue's for later so that the
 156         * key can be evicted from them.  This is needed because some keys
 157         * aren't destroyed until after the filesystem was already unmounted
 158         * (namely, the per-mode keys in struct fscrypt_master_key).
 159         */
 160        for (i = 0; i < num_devs; i++) {
 161                if (!blk_get_queue(blk_key->devs[i])) {
 162                        fscrypt_err(inode, "couldn't get request_queue");
 163                        err = -EAGAIN;
 164                        goto fail;
 165                }
 166                queue_refs++;
 167
 168                err = blk_crypto_start_using_key(&blk_key->base,
 169                                                 blk_key->devs[i]);
 170                if (err) {
 171                        fscrypt_err(inode,
 172                                    "error %d starting to use blk-crypto", err);
 173                        goto fail;
 174                }
 175        }
 176        /*
 177         * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
 178         * I.e., here we publish ->blk_key with a RELEASE barrier so that
 179         * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
 180         * possible for per-mode keys, not for per-file keys.
 181         */
 182        smp_store_release(&prep_key->blk_key, blk_key);
 183        return 0;
 184
 185fail:
 186        for (i = 0; i < queue_refs; i++)
 187                blk_put_queue(blk_key->devs[i]);
 188        kfree_sensitive(blk_key);
 189        return err;
 190}
 191
 192void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
 193{
 194        struct fscrypt_blk_crypto_key *blk_key = prep_key->blk_key;
 195        int i;
 196
 197        if (blk_key) {
 198                for (i = 0; i < blk_key->num_devs; i++) {
 199                        blk_crypto_evict_key(blk_key->devs[i], &blk_key->base);
 200                        blk_put_queue(blk_key->devs[i]);
 201                }
 202                kfree_sensitive(blk_key);
 203        }
 204}
 205
 206bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
 207{
 208        return inode->i_crypt_info->ci_inlinecrypt;
 209}
 210EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
 211
 212static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
 213                                 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
 214{
 215        union fscrypt_iv iv;
 216        int i;
 217
 218        fscrypt_generate_iv(&iv, lblk_num, ci);
 219
 220        BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
 221        memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
 222        for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
 223                dun[i] = le64_to_cpu(iv.dun[i]);
 224}
 225
 226/**
 227 * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
 228 * @bio: a bio which will eventually be submitted to the file
 229 * @inode: the file's inode
 230 * @first_lblk: the first file logical block number in the I/O
 231 * @gfp_mask: memory allocation flags - these must be a waiting mask so that
 232 *                                      bio_crypt_set_ctx can't fail.
 233 *
 234 * If the contents of the file should be encrypted (or decrypted) with inline
 235 * encryption, then assign the appropriate encryption context to the bio.
 236 *
 237 * Normally the bio should be newly allocated (i.e. no pages added yet), as
 238 * otherwise fscrypt_mergeable_bio() won't work as intended.
 239 *
 240 * The encryption context will be freed automatically when the bio is freed.
 241 */
 242void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
 243                               u64 first_lblk, gfp_t gfp_mask)
 244{
 245        const struct fscrypt_info *ci;
 246        u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
 247
 248        if (!fscrypt_inode_uses_inline_crypto(inode))
 249                return;
 250        ci = inode->i_crypt_info;
 251
 252        fscrypt_generate_dun(ci, first_lblk, dun);
 253        bio_crypt_set_ctx(bio, &ci->ci_enc_key.blk_key->base, dun, gfp_mask);
 254}
 255EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
 256
 257/* Extract the inode and logical block number from a buffer_head. */
 258static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
 259                                      const struct inode **inode_ret,
 260                                      u64 *lblk_num_ret)
 261{
 262        struct page *page = bh->b_page;
 263        const struct address_space *mapping;
 264        const struct inode *inode;
 265
 266        /*
 267         * The ext4 journal (jbd2) can submit a buffer_head it directly created
 268         * for a non-pagecache page.  fscrypt doesn't care about these.
 269         */
 270        mapping = page_mapping(page);
 271        if (!mapping)
 272                return false;
 273        inode = mapping->host;
 274
 275        *inode_ret = inode;
 276        *lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
 277                        (bh_offset(bh) >> inode->i_blkbits);
 278        return true;
 279}
 280
 281/**
 282 * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
 283 *                                  crypto
 284 * @bio: a bio which will eventually be submitted to the file
 285 * @first_bh: the first buffer_head for which I/O will be submitted
 286 * @gfp_mask: memory allocation flags
 287 *
 288 * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
 289 * of an inode and block number directly.
 290 */
 291void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
 292                                  const struct buffer_head *first_bh,
 293                                  gfp_t gfp_mask)
 294{
 295        const struct inode *inode;
 296        u64 first_lblk;
 297
 298        if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
 299                fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
 300}
 301EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
 302
 303/**
 304 * fscrypt_mergeable_bio() - test whether data can be added to a bio
 305 * @bio: the bio being built up
 306 * @inode: the inode for the next part of the I/O
 307 * @next_lblk: the next file logical block number in the I/O
 308 *
 309 * When building a bio which may contain data which should undergo inline
 310 * encryption (or decryption) via fscrypt, filesystems should call this function
 311 * to ensure that the resulting bio contains only contiguous data unit numbers.
 312 * This will return false if the next part of the I/O cannot be merged with the
 313 * bio because either the encryption key would be different or the encryption
 314 * data unit numbers would be discontiguous.
 315 *
 316 * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
 317 *
 318 * Return: true iff the I/O is mergeable
 319 */
 320bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 321                           u64 next_lblk)
 322{
 323        const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
 324        u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
 325
 326        if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
 327                return false;
 328        if (!bc)
 329                return true;
 330
 331        /*
 332         * Comparing the key pointers is good enough, as all I/O for each key
 333         * uses the same pointer.  I.e., there's currently no need to support
 334         * merging requests where the keys are the same but the pointers differ.
 335         */
 336        if (bc->bc_key != &inode->i_crypt_info->ci_enc_key.blk_key->base)
 337                return false;
 338
 339        fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
 340        return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
 341}
 342EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
 343
 344/**
 345 * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
 346 * @bio: the bio being built up
 347 * @next_bh: the next buffer_head for which I/O will be submitted
 348 *
 349 * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
 350 * an inode and block number directly.
 351 *
 352 * Return: true iff the I/O is mergeable
 353 */
 354bool fscrypt_mergeable_bio_bh(struct bio *bio,
 355                              const struct buffer_head *next_bh)
 356{
 357        const struct inode *inode;
 358        u64 next_lblk;
 359
 360        if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
 361                return !bio->bi_crypt_context;
 362
 363        return fscrypt_mergeable_bio(bio, inode, next_lblk);
 364}
 365EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
 366