[v5,1/7] fscrypt: Add functions for direct I/O support

Commit Message

Satya Tangirala July 24, 2020, 12:11 p.m. UTC

From: Eric Biggers <[e-mail]>

Introduce fscrypt_dio_supported() to check whether a direct I/O request
is unsupported due to encryption constraints.

Also introduce fscrypt_limit_io_blocks() to limit how many blocks can be
added to a bio being prepared for direct I/O. This is needed for
filesystems that use the iomap direct I/O implementation to avoid DUN
wraparound in the middle of a bio (which is possible with the
IV_INO_LBLK_32 IV generation method). Elsewhere fscrypt_mergeable_bio()
is used for this, but iomap operates on logical ranges directly, so
filesystems using iomap won't have a chance to call fscrypt_mergeable_bio()
on every block added to a bio. So we need this function which limits a
logical range in one go.

Signed-off-by: Eric Biggers <[e-mail]>
Co-developed-by: Satya Tangirala <[e-mail]>
Signed-off-by: Satya Tangirala <[e-mail]>
Reviewed-by: Jaegeuk Kim <[e-mail]>
---
 fs/crypto/crypto.c       |  8 +++++
 fs/crypto/inline_crypt.c | 75 ++++++++++++++++++++++++++++++++++++++++
 include/linux/fscrypt.h  | 19 ++++++++++
 3 files changed, 102 insertions(+)

Comments

Eric Biggers July 24, 2020, 4:46 p.m. UTC | #1

On Fri, Jul 24, 2020 at 12:11:37PM +0000, Satya Tangirala wrote:
> From: Eric Biggers <[e-mail]>
> 
> Introduce fscrypt_dio_supported() to check whether a direct I/O request
> is unsupported due to encryption constraints.
> 
> Also introduce fscrypt_limit_io_blocks() to limit how many blocks can be
> added to a bio being prepared for direct I/O. This is needed for
> filesystems that use the iomap direct I/O implementation to avoid DUN
> wraparound in the middle of a bio (which is possible with the
> IV_INO_LBLK_32 IV generation method). Elsewhere fscrypt_mergeable_bio()
> is used for this, but iomap operates on logical ranges directly, so
> filesystems using iomap won't have a chance to call fscrypt_mergeable_bio()
> on every block added to a bio. So we need this function which limits a
> logical range in one go.
> 
> Signed-off-by: Eric Biggers <[e-mail]>
> Co-developed-by: Satya Tangirala <[e-mail]>
> Signed-off-by: Satya Tangirala <[e-mail]>
> Reviewed-by: Jaegeuk Kim <[e-mail]>

Note, generally you should drop Reviewed-by tags if you make nontrivial changes.

> +/**
> + * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
> + * @inode: the file on which I/O is being done
> + * @pos: the file position (in bytes) at which the I/O is being done
> + * @nr_blocks: the number of blocks we want to submit starting at @pos
> + *
> + * Determine the limit to the number of blocks that can be submitted in the bio
> + * targeting @pos without causing a data unit number (DUN) discontinuity.
> + *
> + * This is normally just @nr_blocks, as normally the DUNs just increment along
> + * with the logical blocks.  (Or the file is not encrypted.)
> + *
> + * In rare cases, fscrypt can be using an IV generation method that allows the
> + * DUN to wrap around within logically continuous blocks, and that wraparound
> + * will occur.  If this happens, a value less than @nr_blocks will be returned
> + * so that the wraparound doesn't occur in the middle of the bio.
> + *
> + * Return: the actual number of blocks that can be submitted
> + */
> +int fscrypt_limit_io_blocks(const struct inode *inode, loff_t pos,
> +			    unsigned int nr_blocks)

ext4 actually passes a block number for the second argument, not a position.

Also, we should make this ready for 64-bit block numbers.  When it's trivial to
do, we keep fs/crypto/ ready for 64-bit block numbers, even though it's not
needed yet.  E.g. see fscrypt_crypt_block() and fscrypt_generate_iv().

It's true that currently this function is a no-op except for IV_INO_LBLK_32, but
that's more of an implementation detail.

So the prototype I recommend is:

u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks);

> +{
> +	const struct fscrypt_info *ci = inode->i_crypt_info;
> +	u32 dun;
> +
> +	if (!fscrypt_inode_uses_inline_crypto(inode))
> +		return nr_blocks;
> +
> +	if (nr_blocks <= 1)
> +		return nr_blocks;
> +
> +	if (!(fscrypt_policy_flags(&ci->ci_policy) &
> +	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
> +		return nr_blocks;
> +
> +	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
> +
> +	dun = ci->ci_hashed_ino + (pos >> inode->i_blkbits);
> +
> +	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
> +}
> diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
> index bb257411365f..241266cba21f 100644
> --- a/include/linux/fscrypt.h
> +++ b/include/linux/fscrypt.h
> @@ -559,6 +559,11 @@ bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
>  bool fscrypt_mergeable_bio_bh(struct bio *bio,
>  			      const struct buffer_head *next_bh);
>  
> +bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter);
> +
> +int fscrypt_limit_io_blocks(const struct inode *inode, loff_t pos,
> +			    unsigned int nr_blocks);
> +
>  #else /* CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
>  
>  static inline bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
> @@ -587,6 +592,20 @@ static inline bool fscrypt_mergeable_bio_bh(struct bio *bio,
>  {
>  	return true;
>  }
> +
> +static inline bool fscrypt_dio_supported(struct kiocb *iocb,
> +					 struct iov_iter *iter)
> +{
> +	const struct inode *inode = file_inode(iocb->ki_filp);
> +
> +	return !fscrypt_needs_contents_encryption(inode);
> +}
> +
> +static inline int fscrypt_limit_io_blocks(const struct inode *inode, loff_t pos,
> +					  unsigned int nr_blocks)
> +{
> +	return nr_blocks;
> +}
>  #endif /* !CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
>  
>  /**
> -- 
> 2.28.0.rc0.142.g3c755180ce-goog
>

Patch

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index a52cf32733ab..d2e933eb98dd 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -69,6 +69,14 @@  void fscrypt_free_bounce_page(struct page *bounce_page)
 }
 EXPORT_SYMBOL(fscrypt_free_bounce_page);
 
+/*
+ * Generate the IV for the given logical block number within the given file.
+ * For filenames encryption, lblk_num == 0.
+ *
+ * Keep this in sync with fscrypt_limit_io_blocks().  fscrypt_limit_io_blocks()
+ * needs to know about any IV generation methods where the low bits of IV don't
+ * simply contain the lblk_num (e.g., IV_INO_LBLK_32).
+ */
 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 			 const struct fscrypt_info *ci)
 {
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index d7aecadf33c1..2cac0da0bd04 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -16,6 +16,7 @@ 
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
 #include <linux/sched/mm.h>
+#include <linux/uio.h>
 
 #include "fscrypt_private.h"
 
@@ -362,3 +363,77 @@  bool fscrypt_mergeable_bio_bh(struct bio *bio,
 	return fscrypt_mergeable_bio(bio, inode, next_lblk);
 }
 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
+
+/**
+ * fscrypt_dio_supported() - check whether a direct I/O request is unsupported
+ *			     due to encryption constraints
+ * @iocb: the file and position the I/O is targeting
+ * @iter: the I/O data segment(s)
+ *
+ * Return: true if direct I/O is supported
+ */
+bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
+{
+	const struct inode *inode = file_inode(iocb->ki_filp);
+	const unsigned int blocksize = i_blocksize(inode);
+
+	/* If the file is unencrypted, no veto from us. */
+	if (!fscrypt_needs_contents_encryption(inode))
+		return true;
+
+	/* We only support direct I/O with inline crypto, not fs-layer crypto */
+	if (!fscrypt_inode_uses_inline_crypto(inode))
+		return false;
+
+	/*
+	 * Since the granularity of encryption is filesystem blocks, the I/O
+	 * must be block aligned -- not just disk sector aligned.
+	 */
+	if (!IS_ALIGNED(iocb->ki_pos | iov_iter_alignment(iter), blocksize))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
+
+/**
+ * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
+ * @inode: the file on which I/O is being done
+ * @pos: the file position (in bytes) at which the I/O is being done
+ * @nr_blocks: the number of blocks we want to submit starting at @pos
+ *
+ * Determine the limit to the number of blocks that can be submitted in the bio
+ * targeting @pos without causing a data unit number (DUN) discontinuity.
+ *
+ * This is normally just @nr_blocks, as normally the DUNs just increment along
+ * with the logical blocks.  (Or the file is not encrypted.)
+ *
+ * In rare cases, fscrypt can be using an IV generation method that allows the
+ * DUN to wrap around within logically continuous blocks, and that wraparound
+ * will occur.  If this happens, a value less than @nr_blocks will be returned
+ * so that the wraparound doesn't occur in the middle of the bio.
+ *
+ * Return: the actual number of blocks that can be submitted
+ */
+int fscrypt_limit_io_blocks(const struct inode *inode, loff_t pos,
+			    unsigned int nr_blocks)
+{
+	const struct fscrypt_info *ci = inode->i_crypt_info;
+	u32 dun;
+
+	if (!fscrypt_inode_uses_inline_crypto(inode))
+		return nr_blocks;
+
+	if (nr_blocks <= 1)
+		return nr_blocks;
+
+	if (!(fscrypt_policy_flags(&ci->ci_policy) &
+	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
+		return nr_blocks;
+
+	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
+
+	dun = ci->ci_hashed_ino + (pos >> inode->i_blkbits);
+
+	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
+}
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index bb257411365f..241266cba21f 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -559,6 +559,11 @@  bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 bool fscrypt_mergeable_bio_bh(struct bio *bio,
 			      const struct buffer_head *next_bh);
 
+bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter);
+
+int fscrypt_limit_io_blocks(const struct inode *inode, loff_t pos,
+			    unsigned int nr_blocks);
+
 #else /* CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
 
 static inline bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
@@ -587,6 +592,20 @@  static inline bool fscrypt_mergeable_bio_bh(struct bio *bio,
 {
 	return true;
 }
+
+static inline bool fscrypt_dio_supported(struct kiocb *iocb,
+					 struct iov_iter *iter)
+{
+	const struct inode *inode = file_inode(iocb->ki_filp);
+
+	return !fscrypt_needs_contents_encryption(inode);
+}
+
+static inline int fscrypt_limit_io_blocks(const struct inode *inode, loff_t pos,
+					  unsigned int nr_blocks)
+{
+	return nr_blocks;
+}
 #endif /* !CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
 
 /**