ext4 crypto: add ext4 encryption facilities

On encrypt, we will re-assign the buffer_heads to point to a bounce
page rather than the control_page (which is the original page to write
that contains the plaintext). The block I/O occurs against the bounce
page.  On write completion, we re-assign the buffer_heads to the
original plaintext page.

On decrypt, we will attach a read completion callback to the bio
struct. This read completion will decrypt the read contents in-place
prior to setting the page up-to-date.

The current encryption mode, AES-256-XTS, lacks cryptographic
integrity. AES-256-GCM is in-plan, but we will need to devise a
mechanism for handling the integrity data.
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <ildarm@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/Makefile

@@ -12,4 +12,4 @@ ext4-y	:= balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
 
 ext4-$(CONFIG_EXT4_FS_POSIX_ACL)	+= acl.o
 ext4-$(CONFIG_EXT4_FS_SECURITY)		+= xattr_security.o
-ext4-$(CONFIG_EXT4_FS_ENCRYPTION)	+= crypto_policy.o
+ext4-$(CONFIG_EXT4_FS_ENCRYPTION)	+= crypto_policy.o crypto.o

fs/ext4/crypto_policy.c

@@ -52,6 +52,13 @@ static int ext4_create_encryption_context_from_policy(
 	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
 	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
 	       EXT4_KEY_DESCRIPTOR_SIZE);
+	if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
+		printk(KERN_WARNING
+		       "%s: Invalid contents encryption mode %d\n", __func__,
+			policy->contents_encryption_mode);
+		res = -EINVAL;
+		goto out;
+	}
 	ctx.contents_encryption_mode = policy->contents_encryption_mode;
 	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
 	BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
@@ -60,6 +67,7 @@ static int ext4_create_encryption_context_from_policy(
 	res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 			     sizeof(ctx), 0);
+out:
 	if (!res)
 		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
 	return res;

fs/ext4/ext4.h

@@ -951,6 +951,11 @@ struct ext4_inode_info {
 
 	/* Precomputed uuid+inum+igen checksum for seeding inode checksums */
 	__u32 i_csum_seed;
+
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	/* Encryption params */
+	struct ext4_encryption_key i_encryption_key;
+#endif
 };
 
 /*
@@ -1366,6 +1371,12 @@ struct ext4_sb_info {
 	struct ratelimit_state s_err_ratelimit_state;
 	struct ratelimit_state s_warning_ratelimit_state;
 	struct ratelimit_state s_msg_ratelimit_state;
+
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	/* Encryption */
+	uint32_t s_file_encryption_mode;
+	uint32_t s_dir_encryption_mode;
+#endif
 };
 
 static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
@@ -1481,6 +1492,18 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 #define EXT4_SB(sb)	(sb)
 #endif
 
+/*
+ * Returns true if the inode is inode is encrypted
+ */
+static inline int ext4_encrypted_inode(struct inode *inode)
+{
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	return ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT);
+#else
+	return 0;
+#endif
+}
+
 #define NEXT_ORPHAN(inode) EXT4_I(inode)->i_dtime
 
 /*
@@ -2026,6 +2049,35 @@ int ext4_process_policy(const struct ext4_encryption_policy *policy,
 int ext4_get_policy(struct inode *inode,
 		    struct ext4_encryption_policy *policy);
 
+/* crypto.c */
+bool ext4_valid_contents_enc_mode(uint32_t mode);
+uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size);
+extern struct workqueue_struct *ext4_read_workqueue;
+struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode);
+void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx);
+void ext4_restore_control_page(struct page *data_page);
+struct page *ext4_encrypt(struct inode *inode,
+			  struct page *plaintext_page);
+int ext4_decrypt(struct ext4_crypto_ctx *ctx, struct page *page);
+int ext4_decrypt_one(struct inode *inode, struct page *page);
+int ext4_encrypted_zeroout(struct inode *inode, struct ext4_extent *ex);
+
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+int ext4_init_crypto(void);
+void ext4_exit_crypto(void);
+static inline int ext4_sb_has_crypto(struct super_block *sb)
+{
+	return EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_ENCRYPT);
+}
+#else
+static inline int ext4_init_crypto(void) { return 0; }
+static inline void ext4_exit_crypto(void) { }
+static inline int ext4_sb_has_crypto(struct super_block *sb)
+{
+	return 0;
+}
+#endif
+
 /* dir.c */
 extern int __ext4_check_dir_entry(const char *, unsigned int, struct inode *,
 				  struct file *,

fs/ext4/ext4_crypto.h

@@ -46,4 +46,59 @@ struct ext4_encryption_context {
 	char nonce[EXT4_KEY_DERIVATION_NONCE_SIZE];
 } __attribute__((__packed__));
 
+/* Encryption parameters */
+#define EXT4_XTS_TWEAK_SIZE 16
+#define EXT4_AES_128_ECB_KEY_SIZE 16
+#define EXT4_AES_256_GCM_KEY_SIZE 32
+#define EXT4_AES_256_CBC_KEY_SIZE 32
+#define EXT4_AES_256_CTS_KEY_SIZE 32
+#define EXT4_AES_256_XTS_KEY_SIZE 64
+#define EXT4_MAX_KEY_SIZE 64
+
+struct ext4_encryption_key {
+	uint32_t mode;
+	char raw[EXT4_MAX_KEY_SIZE];
+	uint32_t size;
+};
+
+#define EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL             0x00000001
+#define EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL     0x00000002
+
+struct ext4_crypto_ctx {
+	struct crypto_tfm *tfm;         /* Crypto API context */
+	struct page *bounce_page;       /* Ciphertext page on write path */
+	struct page *control_page;      /* Original page on write path */
+	struct bio *bio;                /* The bio for this context */
+	struct work_struct work;        /* Work queue for read complete path */
+	struct list_head free_list;     /* Free list */
+	int flags;                      /* Flags */
+	int mode;                       /* Encryption mode for tfm */
+};
+
+struct ext4_completion_result {
+	struct completion completion;
+	int res;
+};
+
+#define DECLARE_EXT4_COMPLETION_RESULT(ecr) \
+	struct ext4_completion_result ecr = { \
+		COMPLETION_INITIALIZER((ecr).completion), 0 }
+
+static inline int ext4_encryption_key_size(int mode)
+{
+	switch (mode) {
+	case EXT4_ENCRYPTION_MODE_AES_256_XTS:
+		return EXT4_AES_256_XTS_KEY_SIZE;
+	case EXT4_ENCRYPTION_MODE_AES_256_GCM:
+		return EXT4_AES_256_GCM_KEY_SIZE;
+	case EXT4_ENCRYPTION_MODE_AES_256_CBC:
+		return EXT4_AES_256_CBC_KEY_SIZE;
+	case EXT4_ENCRYPTION_MODE_AES_256_CTS:
+		return EXT4_AES_256_CTS_KEY_SIZE;
+	default:
+		BUG();
+	}
+	return 0;
+}
+
 #endif	/* _EXT4_CRYPTO_H */

fs/ext4/super.c

@@ -876,6 +876,9 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
 	atomic_set(&ei->i_ioend_count, 0);
 	atomic_set(&ei->i_unwritten, 0);
 	INIT_WORK(&ei->i_rsv_conversion_work, ext4_end_io_rsv_work);
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	ei->i_encryption_key.mode = EXT4_ENCRYPTION_MODE_INVALID;
+#endif
 
 	return &ei->vfs_inode;
 }
@@ -3431,6 +3434,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (sb->s_bdev->bd_part)
 		sbi->s_sectors_written_start =
 			part_stat_read(sb->s_bdev->bd_part, sectors[1]);
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	/* Modes of operations for file and directory encryption. */
+	sbi->s_file_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
+	sbi->s_dir_encryption_mode = EXT4_ENCRYPTION_MODE_INVALID;
+#endif
 
 	/* Cleanup superblock name */
 	for (cp = sb->s_id; (cp = strchr(cp, '/'));)