diff mbox series

[2/3] fscrypt: Add metadata encryption support

Message ID 20201005073606.1949772-3-satyat@google.com
State New
Headers show
Series add support for metadata encryption to F2FS | expand

Commit Message

Satya Tangirala Oct. 5, 2020, 7:36 a.m. UTC
Introduces functions that help with metadata encryption.

In particular, we introduce:

fscrypt_setup_metadata_encryption() - filesystems should call this function
to set up metadata encryption on a super block with the encryption
algorithm (the desired FSCRYPT_MODE_*) and the key descriptor of the
encryption key. The key descriptor is looked up in the logon keyring of the
current session using "fscrypt:" as the descriptor prefix.

fscrypt_metadata_crypt_bio() - filesystems should call this function on a
bio that it wants metadata crypted. This function will set a bio-crypt-ctx
on the bio if the metadata key was set up with
fscrypt_setup_metadata_encryption(). The DUN for the first block in the bio
is the offset of that block from the start of the filesystem.

fscrypt_free_metadata_encryption() - this function should be called when
the super block is being freed. It ensures that the metadata encryption key
is evicted, if necessary, from devices.

Note that the filesystem (rather than fscrypt) controls precisely which
blocks are encrypted with the metadata encryption key and which blocks are
encrypted with other keys/not encrypted at all. Fscrypt only provides some
convenience functions that ultimately help encrypt a bio with the metadata
encryption key when desired.

Signed-off-by: Satya Tangirala <satyat@google.com>
---
 fs/crypto/Kconfig           |   6 +
 fs/crypto/Makefile          |   1 +
 fs/crypto/fscrypt_private.h |  19 ++++
 fs/crypto/inline_crypt.c    |  18 ---
 fs/crypto/metadata_crypt.c  | 220 ++++++++++++++++++++++++++++++++++++
 include/linux/fs.h          |   3 +
 include/linux/fscrypt.h     |  47 ++++++++
 7 files changed, 296 insertions(+), 18 deletions(-)
 create mode 100644 fs/crypto/metadata_crypt.c

Comments

Eric Biggers Oct. 7, 2020, 8:52 p.m. UTC | #1
On Mon, Oct 05, 2020 at 07:36:05AM +0000, Satya Tangirala wrote:
> Introduces functions that help with metadata encryption.
> 
> In particular, we introduce:
> 
> fscrypt_setup_metadata_encryption() - filesystems should call this function
> to set up metadata encryption on a super block with the encryption
> algorithm (the desired FSCRYPT_MODE_*) and the key descriptor of the
> encryption key. The key descriptor is looked up in the logon keyring of the
> current session using "fscrypt:" as the descriptor prefix.
> 
> fscrypt_metadata_crypt_bio() - filesystems should call this function on a
> bio that it wants metadata crypted. This function will set a bio-crypt-ctx
> on the bio if the metadata key was set up with
> fscrypt_setup_metadata_encryption(). The DUN for the first block in the bio
> is the offset of that block from the start of the filesystem.
> 
> fscrypt_free_metadata_encryption() - this function should be called when
> the super block is being freed. It ensures that the metadata encryption key
> is evicted, if necessary, from devices.
> 
> Note that the filesystem (rather than fscrypt) controls precisely which
> blocks are encrypted with the metadata encryption key and which blocks are
> encrypted with other keys/not encrypted at all. Fscrypt only provides some
> convenience functions that ultimately help encrypt a bio with the metadata
> encryption key when desired.
> 
> Signed-off-by: Satya Tangirala <satyat@google.com>
> ---
>  fs/crypto/Kconfig           |   6 +
>  fs/crypto/Makefile          |   1 +
>  fs/crypto/fscrypt_private.h |  19 ++++
>  fs/crypto/inline_crypt.c    |  18 ---
>  fs/crypto/metadata_crypt.c  | 220 ++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h          |   3 +
>  include/linux/fscrypt.h     |  47 ++++++++
>  7 files changed, 296 insertions(+), 18 deletions(-)
>  create mode 100644 fs/crypto/metadata_crypt.c
> 
> diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
> index a5f5c30368a2..3010e91f6659 100644
> --- a/fs/crypto/Kconfig
> +++ b/fs/crypto/Kconfig
> @@ -30,3 +30,9 @@ config FS_ENCRYPTION_INLINE_CRYPT
>  	depends on FS_ENCRYPTION && BLK_INLINE_ENCRYPTION
>  	help
>  	  Enable fscrypt to use inline encryption hardware if available.
> +
> +config FS_ENCRYPTION_METADATA
> +	bool "Enable metadata encryption with fscrypt"
> +	depends on FS_ENCRYPTION && BLK_INLINE_ENCRYPTION
> +	help
> +	  Enable fscrypt to encrypt metadata.

This needs Kconfig help text to describe what this feature is and why anyone
would want to enable it.  It also needs an update to
Documentation/filesystems/fscrypt.rst, and a test in xfstests that tests that
the encryption is being done correctly.

> diff --git a/fs/crypto/metadata_crypt.c b/fs/crypto/metadata_crypt.c
> new file mode 100644
> index 000000000000..5e16df130509
> --- /dev/null
> +++ b/fs/crypto/metadata_crypt.c
> @@ -0,0 +1,220 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Metadata encryption support for fscrypt
> + *
> + * Copyright 2020 Google LLC
> + */
> +
> +#include <keys/user-type.h>
> +#include <linux/blk-crypto.h>
> +#include <linux/blkdev.h>
> +#include <linux/buffer_head.h>
> +#include <linux/sched/mm.h>
> +
> +#include "fscrypt_private.h"
> +
> +/* TODO: mostly copied from keysetup_v1.c - maybe refactor this function */
> +static int fscrypt_metadata_get_key_from_id(const char *prefix,
> +					    char *descriptor_hex,
> +					    unsigned int min_keysize,
> +					    char *raw_key)
> +{
> +	char *description;
> +	struct key *key;
> +	const struct user_key_payload *ukp;
> +	const struct fscrypt_key *payload;
> +	int err = -ENOKEY;
> +
> +	if (strlen(descriptor_hex) != FSCRYPT_KEY_DESCRIPTOR_SIZE * 2)
> +		return -EINVAL;
> +
> +	description = kasprintf(GFP_NOFS, "%s%s", prefix, descriptor_hex);
> +	if (!description)
> +		return -ENOMEM;
> +
> +	key = request_key(&key_type_logon, description, NULL);
> +	kfree(description);
> +	if (IS_ERR(key))
> +		return PTR_ERR(key);
> +
> +	down_read(&key->sem);
> +	ukp = user_key_payload_locked(key);
> +
> +	if (!ukp) /* was the key revoked before we acquired its semaphore? */
> +		goto out;
> +
> +	payload = (const struct fscrypt_key *)ukp->data;

'struct fscrypt_key' was a mistake.  How about having the key payload just be
the raw key?

Or are you thinking that reserved fields will be needed?

> +/**
> + * fscrypt_setup_metadata_encryption() - prepare a super_block for metadata
> + *					 encryption
> + * @sb: The super_block to set up metadata encryption for
> + * @key_desc_hex: The key descriptor (in hex) to look for in the logon keyring.

There's no such thing as a "logon keyring".  I think you mean "look for a logon
key in the process-subscribed keyrings".

> + * @fscrypt_mode_num: The FSCRYPT_MODE_* to use as the encryption algorithm.
> + *
> + * Return: 0 on success, negative number on error.
> + */
> +int fscrypt_setup_metadata_encryption(struct super_block *sb,
> +				      char *key_desc_hex,
> +				      int fscrypt_mode_num)
> +{
> +	int err = 0;
> +	enum blk_crypto_mode_num crypto_mode;
> +	unsigned int lblk_bits = 64;
> +	unsigned int dun_bytes;
> +	unsigned int dummy;
> +	char raw_key[FSCRYPT_MAX_KEY_SIZE];

For binary data, prefer 'u8' to 'char'.

> +
> +	if (fscrypt_mode_num > __FSCRYPT_MODE_MAX || fscrypt_mode_num < 0 ||
> +	    !fscrypt_modes[fscrypt_mode_num].cipher_str) {
> +		fscrypt_warn(NULL, "Invalid fscrypt mode %d specified for metadata encryption.",
> +			     fscrypt_mode_num);
> +		return -EOPNOTSUPP;
> +	}

The filenames-only encryption modes (FSCRYPT_MODE_AES_256_CTS and
FSCRYPT_MODE_AES_128_CTS) will pass this check, which seems undesired.

> +
> +	if (sb->s_cop->get_ino_and_lblk_bits)
> +		sb->s_cop->get_ino_and_lblk_bits(sb, &dummy, &lblk_bits);
> +	dun_bytes = DIV_ROUND_UP(lblk_bits, 8);
> +
> +	if (fscrypt_modes[fscrypt_mode_num].ivsize < dun_bytes) {
> +		fscrypt_warn(NULL, "The fscrypt mode only supports %d DUN bytes, but FS requires support for %d DUN bytes.",
> +			     fscrypt_modes[fscrypt_mode_num].ivsize, dun_bytes);
> +		return -EOPNOTSUPP;
> +	}

lblk_bits is the number of bits used to represent file logical block numbers
(e.g. ext4_lblk_t).  That's different from the filesystem-wide block number
(e.g. ext4_fsblk_t), which is what metadata encryption will use.

> +	crypto_mode = fscrypt_modes[fscrypt_mode_num].blk_crypto_mode;
> +
> +	err = fscrypt_metadata_get_key_from_id(
> +					FSCRYPT_KEY_DESC_PREFIX,
> +					key_desc_hex,
> +					fscrypt_modes[fscrypt_mode_num].keysize,
> +					raw_key);
> +	if (err)
> +		goto out;

This is allowing for the key to be longer than the provided keysize, in which
case only a prefix of the key is used.

It should require the exact keysize instead.

> +
> +	sb->s_metadata_key = kzalloc(sizeof(*sb->s_metadata_key), GFP_NOFS);

No need for GFP_NOFS here.

> +/**
> + * fscrypt_free_metadata_encryption() - free metadata encryption fields in
> + *					super_block.
> + * @sb: The super_block to free metatdata encryption fields from
> + */
> +void fscrypt_free_metadata_encryption(struct super_block *sb)
> +{
> +	int num_devices;
> +	int i;
> +	struct request_queue *q;
> +
> +	if (!sb->s_metadata_key)
> +		return;
> +
> +	num_devices = fscrypt_get_num_devices(sb);
> +
> +	for (i = 0; i < num_devices; i++) {
> +		q = fscrypt_get_device(sb, i);
> +		if (WARN_ON(!q))
> +			continue;
> +		blk_crypto_evict_key(q, sb->s_metadata_key);
> +	}
> +
> +	memzero_explicit(sb->s_metadata_key, sizeof(*sb->s_metadata_key));
> +	kzfree(sb->s_metadata_key);
> +	sb->s_metadata_key = NULL;
> +}

kfree_sensitive(), not kzfree().

Also, memzero_explicit() is redundant.

> +/**
> + * fscrypt_metadata_crypt_bio() - Add metadata encryption context to bio.
> + *
> + * @bio: The bio to add the encryption context to
> + * @lblk: The logical block number within the filesystem at which this bio
> + *	  starts reading/writing data.

Should be:

   @fsblk: The block number within the filesystem ...

> + * @sb: The superblock of the filesystem
> + * @gfp_mask: gfp_mask for bio_crypt_context allocation
> + */
> +void fscrypt_metadata_crypt_bio(struct bio *bio, u64 lblk,
> +				struct super_block *sb, gfp_t gfp_mask)
> +{
> +	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE] = { 0 };
> +
> +	if (!sb->s_metadata_key)
> +		return;
> +
> +	dun[0] = lblk;
> +	bio_crypt_set_ctx(bio, sb->s_metadata_key, dun, gfp_mask);
> +}

Perhaps fscrypt_set_bio_crypt_ctx() should call this?  It seems there should be
a single function that filesystems can call that handles setting the
bio_crypt_ctx for both file contents and metadata encryption.

- Eric
Satya Tangirala Oct. 7, 2020, 11:28 p.m. UTC | #2
On Wed, Oct 07, 2020 at 01:52:21PM -0700, Eric Biggers wrote:
> On Mon, Oct 05, 2020 at 07:36:05AM +0000, Satya Tangirala wrote:
> > Introduces functions that help with metadata encryption.
> > 
> > In particular, we introduce:
> > 
> > fscrypt_setup_metadata_encryption() - filesystems should call this function
> > to set up metadata encryption on a super block with the encryption
> > algorithm (the desired FSCRYPT_MODE_*) and the key descriptor of the
> > encryption key. The key descriptor is looked up in the logon keyring of the
> > current session using "fscrypt:" as the descriptor prefix.
> > 
> > fscrypt_metadata_crypt_bio() - filesystems should call this function on a
> > bio that it wants metadata crypted. This function will set a bio-crypt-ctx
> > on the bio if the metadata key was set up with
> > fscrypt_setup_metadata_encryption(). The DUN for the first block in the bio
> > is the offset of that block from the start of the filesystem.
> > 
> > fscrypt_free_metadata_encryption() - this function should be called when
> > the super block is being freed. It ensures that the metadata encryption key
> > is evicted, if necessary, from devices.
> > 
> > Note that the filesystem (rather than fscrypt) controls precisely which
> > blocks are encrypted with the metadata encryption key and which blocks are
> > encrypted with other keys/not encrypted at all. Fscrypt only provides some
> > convenience functions that ultimately help encrypt a bio with the metadata
> > encryption key when desired.
> > 
> > Signed-off-by: Satya Tangirala <satyat@google.com>
> > ---
> >  fs/crypto/Kconfig           |   6 +
> >  fs/crypto/Makefile          |   1 +
> >  fs/crypto/fscrypt_private.h |  19 ++++
> >  fs/crypto/inline_crypt.c    |  18 ---
> >  fs/crypto/metadata_crypt.c  | 220 ++++++++++++++++++++++++++++++++++++
> >  include/linux/fs.h          |   3 +
> >  include/linux/fscrypt.h     |  47 ++++++++
> >  7 files changed, 296 insertions(+), 18 deletions(-)
> >  create mode 100644 fs/crypto/metadata_crypt.c
> > 
> > diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
> > index a5f5c30368a2..3010e91f6659 100644
> > --- a/fs/crypto/Kconfig
> > +++ b/fs/crypto/Kconfig
> > @@ -30,3 +30,9 @@ config FS_ENCRYPTION_INLINE_CRYPT
> >  	depends on FS_ENCRYPTION && BLK_INLINE_ENCRYPTION
> >  	help
> >  	  Enable fscrypt to use inline encryption hardware if available.
> > +
> > +config FS_ENCRYPTION_METADATA
> > +	bool "Enable metadata encryption with fscrypt"
> > +	depends on FS_ENCRYPTION && BLK_INLINE_ENCRYPTION
> > +	help
> > +	  Enable fscrypt to encrypt metadata.
> 
> This needs Kconfig help text to describe what this feature is and why anyone
> would want to enable it.  It also needs an update to
> Documentation/filesystems/fscrypt.rst, and a test in xfstests that tests that
> the encryption is being done correctly.
> 
Sure. I forgot to mention, fwiw I did hack xfstests to enable metadata
encryption on each device to try to test the code, and also some other
informal tests, but as you point out, I should send out actual xfstests
to test this.
> > diff --git a/fs/crypto/metadata_crypt.c b/fs/crypto/metadata_crypt.c
> > new file mode 100644
> > index 000000000000..5e16df130509
> > --- /dev/null
> > +++ b/fs/crypto/metadata_crypt.c
> > @@ -0,0 +1,220 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Metadata encryption support for fscrypt
> > + *
> > + * Copyright 2020 Google LLC
> > + */
> > +
> > +#include <keys/user-type.h>
> > +#include <linux/blk-crypto.h>
> > +#include <linux/blkdev.h>
> > +#include <linux/buffer_head.h>
> > +#include <linux/sched/mm.h>
> > +
> > +#include "fscrypt_private.h"
> > +
> > +/* TODO: mostly copied from keysetup_v1.c - maybe refactor this function */
> > +static int fscrypt_metadata_get_key_from_id(const char *prefix,
> > +					    char *descriptor_hex,
> > +					    unsigned int min_keysize,
> > +					    char *raw_key)
> > +{
> > +	char *description;
> > +	struct key *key;
> > +	const struct user_key_payload *ukp;
> > +	const struct fscrypt_key *payload;
> > +	int err = -ENOKEY;
> > +
> > +	if (strlen(descriptor_hex) != FSCRYPT_KEY_DESCRIPTOR_SIZE * 2)
> > +		return -EINVAL;
> > +
> > +	description = kasprintf(GFP_NOFS, "%s%s", prefix, descriptor_hex);
> > +	if (!description)
> > +		return -ENOMEM;
> > +
> > +	key = request_key(&key_type_logon, description, NULL);
> > +	kfree(description);
> > +	if (IS_ERR(key))
> > +		return PTR_ERR(key);
> > +
> > +	down_read(&key->sem);
> > +	ukp = user_key_payload_locked(key);
> > +
> > +	if (!ukp) /* was the key revoked before we acquired its semaphore? */
> > +		goto out;
> > +
> > +	payload = (const struct fscrypt_key *)ukp->data;
> 
> 'struct fscrypt_key' was a mistake.  How about having the key payload just be
> the raw key?
> 
> Or are you thinking that reserved fields will be needed?
> 
Ah, I should've just made it the raw key to start with - I can't think
of any reserved fields we might need when specifying the key (I thought
we might need something like that when we try to support hardware
wrapped keys with metadata encryption, but we could use extra fields in
the superblock for that).

> > +/**
> > + * fscrypt_setup_metadata_encryption() - prepare a super_block for metadata
> > + *					 encryption
> > + * @sb: The super_block to set up metadata encryption for
> > + * @key_desc_hex: The key descriptor (in hex) to look for in the logon keyring.
> 
> There's no such thing as a "logon keyring".  I think you mean "look for a logon
> key in the process-subscribed keyrings".
> 
Ah, I see - thanks!
> > + * @fscrypt_mode_num: The FSCRYPT_MODE_* to use as the encryption algorithm.
> > + *
> > + * Return: 0 on success, negative number on error.
> > + */
> > +int fscrypt_setup_metadata_encryption(struct super_block *sb,
> > +				      char *key_desc_hex,
> > +				      int fscrypt_mode_num)
> > +{
> > +	int err = 0;
> > +	enum blk_crypto_mode_num crypto_mode;
> > +	unsigned int lblk_bits = 64;
> > +	unsigned int dun_bytes;
> > +	unsigned int dummy;
> > +	char raw_key[FSCRYPT_MAX_KEY_SIZE];
> 
> For binary data, prefer 'u8' to 'char'.
> 
> > +
> > +	if (fscrypt_mode_num > __FSCRYPT_MODE_MAX || fscrypt_mode_num < 0 ||
> > +	    !fscrypt_modes[fscrypt_mode_num].cipher_str) {
> > +		fscrypt_warn(NULL, "Invalid fscrypt mode %d specified for metadata encryption.",
> > +			     fscrypt_mode_num);
> > +		return -EOPNOTSUPP;
> > +	}
> 
> The filenames-only encryption modes (FSCRYPT_MODE_AES_256_CTS and
> FSCRYPT_MODE_AES_128_CTS) will pass this check, which seems undesired.
> 
> > +
> > +	if (sb->s_cop->get_ino_and_lblk_bits)
> > +		sb->s_cop->get_ino_and_lblk_bits(sb, &dummy, &lblk_bits);
> > +	dun_bytes = DIV_ROUND_UP(lblk_bits, 8);
> > +
> > +	if (fscrypt_modes[fscrypt_mode_num].ivsize < dun_bytes) {
> > +		fscrypt_warn(NULL, "The fscrypt mode only supports %d DUN bytes, but FS requires support for %d DUN bytes.",
> > +			     fscrypt_modes[fscrypt_mode_num].ivsize, dun_bytes);
> > +		return -EOPNOTSUPP;
> > +	}
> 
> lblk_bits is the number of bits used to represent file logical block numbers
> (e.g. ext4_lblk_t).  That's different from the filesystem-wide block number
> (e.g. ext4_fsblk_t), which is what metadata encryption will use.
> 
> > +	crypto_mode = fscrypt_modes[fscrypt_mode_num].blk_crypto_mode;
> > +
> > +	err = fscrypt_metadata_get_key_from_id(
> > +					FSCRYPT_KEY_DESC_PREFIX,
> > +					key_desc_hex,
> > +					fscrypt_modes[fscrypt_mode_num].keysize,
> > +					raw_key);
> > +	if (err)
> > +		goto out;
> 
> This is allowing for the key to be longer than the provided keysize, in which
> case only a prefix of the key is used.
> 
> It should require the exact keysize instead.
> 
> > +
> > +	sb->s_metadata_key = kzalloc(sizeof(*sb->s_metadata_key), GFP_NOFS);
> 
> No need for GFP_NOFS here.
> 
> > +/**
> > + * fscrypt_free_metadata_encryption() - free metadata encryption fields in
> > + *					super_block.
> > + * @sb: The super_block to free metatdata encryption fields from
> > + */
> > +void fscrypt_free_metadata_encryption(struct super_block *sb)
> > +{
> > +	int num_devices;
> > +	int i;
> > +	struct request_queue *q;
> > +
> > +	if (!sb->s_metadata_key)
> > +		return;
> > +
> > +	num_devices = fscrypt_get_num_devices(sb);
> > +
> > +	for (i = 0; i < num_devices; i++) {
> > +		q = fscrypt_get_device(sb, i);
> > +		if (WARN_ON(!q))
> > +			continue;
> > +		blk_crypto_evict_key(q, sb->s_metadata_key);
> > +	}
> > +
> > +	memzero_explicit(sb->s_metadata_key, sizeof(*sb->s_metadata_key));
> > +	kzfree(sb->s_metadata_key);
> > +	sb->s_metadata_key = NULL;
> > +}
> 
> kfree_sensitive(), not kzfree().
> 
> Also, memzero_explicit() is redundant.
> 
> > +/**
> > + * fscrypt_metadata_crypt_bio() - Add metadata encryption context to bio.
> > + *
> > + * @bio: The bio to add the encryption context to
> > + * @lblk: The logical block number within the filesystem at which this bio
> > + *	  starts reading/writing data.
> 
> Should be:
> 
>    @fsblk: The block number within the filesystem ...
> 
> > + * @sb: The superblock of the filesystem
> > + * @gfp_mask: gfp_mask for bio_crypt_context allocation
> > + */
> > +void fscrypt_metadata_crypt_bio(struct bio *bio, u64 lblk,
> > +				struct super_block *sb, gfp_t gfp_mask)
> > +{
> > +	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE] = { 0 };
> > +
> > +	if (!sb->s_metadata_key)
> > +		return;
> > +
> > +	dun[0] = lblk;
> > +	bio_crypt_set_ctx(bio, sb->s_metadata_key, dun, gfp_mask);
> > +}
> 
> Perhaps fscrypt_set_bio_crypt_ctx() should call this?  It seems there should be
> a single function that filesystems can call that handles setting the
> bio_crypt_ctx for both file contents and metadata encryption.
> 
I mistakenly dismissed this idea when I was coding this up :( - I'll do
this for the next version... I think it'll also make supporting direct I/O
easier in future :) . Also, I might require FS_ENCRYPTION_INLINE_CRYPT
when enabling FS_ENCRYPTION_METADATA to maybe make the code slightly
cleaner (unless there's a reason we want to support metadata encryption
without FS inline encryption being enabled?).
> - Eric
Eric Biggers Oct. 8, 2020, 5:05 p.m. UTC | #3
On Wed, Oct 07, 2020 at 11:28:06PM +0000, Satya Tangirala wrote:
> > This needs Kconfig help text to describe what this feature is and why anyone
> > would want to enable it.  It also needs an update to
> > Documentation/filesystems/fscrypt.rst, and a test in xfstests that tests that
> > the encryption is being done correctly.
> > 
> Sure. I forgot to mention, fwiw I did hack xfstests to enable metadata
> encryption on each device to try to test the code, and also some other
> informal tests, but as you point out, I should send out actual xfstests
> to test this.

To be clear, I'm asking for tests which verify the actual ciphertext written to
disk.  So similar to _verify_ciphertext_for_encryption_policy() in xfstests, or
to vts_kernel_encryption_test in Android's VTS.

> > Perhaps fscrypt_set_bio_crypt_ctx() should call this?  It seems there should be
> > a single function that filesystems can call that handles setting the
> > bio_crypt_ctx for both file contents and metadata encryption.
> > 
> I mistakenly dismissed this idea when I was coding this up :( - I'll do
> this for the next version... I think it'll also make supporting direct I/O
> easier in future :) . Also, I might require FS_ENCRYPTION_INLINE_CRYPT
> when enabling FS_ENCRYPTION_METADATA to maybe make the code slightly
> cleaner (unless there's a reason we want to support metadata encryption
> without FS inline encryption being enabled?).

Since metadata encryption would already depend on FS_ENCRYPTION and
BLK_INLINE_ENCRYPTION, I think it would be fine to require
FS_ENCRYPTION_INLINE_CRYPT too, in order to reduce the number of combinations.

- Eric
diff mbox series

Patch

diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
index a5f5c30368a2..3010e91f6659 100644
--- a/fs/crypto/Kconfig
+++ b/fs/crypto/Kconfig
@@ -30,3 +30,9 @@  config FS_ENCRYPTION_INLINE_CRYPT
 	depends on FS_ENCRYPTION && BLK_INLINE_ENCRYPTION
 	help
 	  Enable fscrypt to use inline encryption hardware if available.
+
+config FS_ENCRYPTION_METADATA
+	bool "Enable metadata encryption with fscrypt"
+	depends on FS_ENCRYPTION && BLK_INLINE_ENCRYPTION
+	help
+	  Enable fscrypt to encrypt metadata.
\ No newline at end of file
diff --git a/fs/crypto/Makefile b/fs/crypto/Makefile
index 652c7180ec6d..8403c7956983 100644
--- a/fs/crypto/Makefile
+++ b/fs/crypto/Makefile
@@ -12,3 +12,4 @@  fscrypto-y := crypto.o \
 
 fscrypto-$(CONFIG_BLOCK) += bio.o
 fscrypto-$(CONFIG_FS_ENCRYPTION_INLINE_CRYPT) += inline_crypt.o
+fscrypto-$(CONFIG_FS_ENCRYPTION_METADATA) += metadata_crypt.o
\ No newline at end of file
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 8117a61b6f55..dca254590a70 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -327,6 +327,25 @@  int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
 void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
 
 /* inline_crypt.c */
+
+static inline int fscrypt_get_num_devices(struct super_block *sb)
+{
+	if (sb->s_cop->get_num_devices)
+		return sb->s_cop->get_num_devices(sb);
+	return 1;
+}
+
+static inline struct request_queue *fscrypt_get_device(struct super_block *sb,
+						unsigned int device_index)
+{
+	if (sb->s_cop->get_device)
+		return sb->s_cop->get_device(sb, device_index);
+	else if (WARN_ON_ONCE(device_index != 0))
+		return NULL;
+	else
+		return bdev_get_queue(sb->s_bdev);
+}
+
 #ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
 int fscrypt_select_encryption_impl(struct fscrypt_info *ci);
 
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index 5bbce79df638..f8f7363ebcd0 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -26,24 +26,6 @@  struct fscrypt_blk_crypto_key {
 	struct request_queue *devs[];
 };
 
-static int fscrypt_get_num_devices(struct super_block *sb)
-{
-	if (sb->s_cop->get_num_devices)
-		return sb->s_cop->get_num_devices(sb);
-	return 1;
-}
-
-static struct request_queue *fscrypt_get_device(struct super_block *sb,
-						unsigned int device_index)
-{
-	if (sb->s_cop->get_device)
-		return sb->s_cop->get_device(sb, device_index);
-	else if (WARN_ON_ONCE(device_index != 0))
-		return NULL;
-	else
-		return bdev_get_queue(sb->s_bdev);
-}
-
 static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci)
 {
 	struct super_block *sb = ci->ci_inode->i_sb;
diff --git a/fs/crypto/metadata_crypt.c b/fs/crypto/metadata_crypt.c
new file mode 100644
index 000000000000..5e16df130509
--- /dev/null
+++ b/fs/crypto/metadata_crypt.c
@@ -0,0 +1,220 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Metadata encryption support for fscrypt
+ *
+ * Copyright 2020 Google LLC
+ */
+
+#include <keys/user-type.h>
+#include <linux/blk-crypto.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>
+#include <linux/sched/mm.h>
+
+#include "fscrypt_private.h"
+
+/* TODO: mostly copied from keysetup_v1.c - maybe refactor this function */
+static int fscrypt_metadata_get_key_from_id(const char *prefix,
+					    char *descriptor_hex,
+					    unsigned int min_keysize,
+					    char *raw_key)
+{
+	char *description;
+	struct key *key;
+	const struct user_key_payload *ukp;
+	const struct fscrypt_key *payload;
+	int err = -ENOKEY;
+
+	if (strlen(descriptor_hex) != FSCRYPT_KEY_DESCRIPTOR_SIZE * 2)
+		return -EINVAL;
+
+	description = kasprintf(GFP_NOFS, "%s%s", prefix, descriptor_hex);
+	if (!description)
+		return -ENOMEM;
+
+	key = request_key(&key_type_logon, description, NULL);
+	kfree(description);
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+
+	down_read(&key->sem);
+	ukp = user_key_payload_locked(key);
+
+	if (!ukp) /* was the key revoked before we acquired its semaphore? */
+		goto out;
+
+	payload = (const struct fscrypt_key *)ukp->data;
+
+	if (ukp->datalen != sizeof(struct fscrypt_key) ||
+	    payload->size < 1 || payload->size > FSCRYPT_MAX_KEY_SIZE) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' has invalid payload",
+			     key->description);
+		goto out;
+	}
+
+	if (payload->size < min_keysize) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
+			     key->description, payload->size, min_keysize);
+		goto out;
+	}
+
+	memcpy(raw_key, payload->raw, min_keysize);
+	err = 0;
+
+out:
+	up_read(&key->sem);
+	key_put(key);
+
+	return err;
+}
+
+/**
+ * fscrypt_setup_metadata_encryption() - prepare a super_block for metadata
+ *					 encryption
+ * @sb: The super_block to set up metadata encryption for
+ * @key_desc_hex: The key descriptor (in hex) to look for in the logon keyring.
+ * @fscrypt_mode_num: The FSCRYPT_MODE_* to use as the encryption algorithm.
+ *
+ * Return: 0 on success, negative number on error.
+ */
+int fscrypt_setup_metadata_encryption(struct super_block *sb,
+				      char *key_desc_hex,
+				      int fscrypt_mode_num)
+{
+	int err = 0;
+	enum blk_crypto_mode_num crypto_mode;
+	unsigned int lblk_bits = 64;
+	unsigned int dun_bytes;
+	unsigned int dummy;
+	char raw_key[FSCRYPT_MAX_KEY_SIZE];
+
+	if (fscrypt_mode_num > __FSCRYPT_MODE_MAX || fscrypt_mode_num < 0 ||
+	    !fscrypt_modes[fscrypt_mode_num].cipher_str) {
+		fscrypt_warn(NULL, "Invalid fscrypt mode %d specified for metadata encryption.",
+			     fscrypt_mode_num);
+		return -EOPNOTSUPP;
+	}
+
+	if (sb->s_cop->get_ino_and_lblk_bits)
+		sb->s_cop->get_ino_and_lblk_bits(sb, &dummy, &lblk_bits);
+	dun_bytes = DIV_ROUND_UP(lblk_bits, 8);
+
+	if (fscrypt_modes[fscrypt_mode_num].ivsize < dun_bytes) {
+		fscrypt_warn(NULL, "The fscrypt mode only supports %d DUN bytes, but FS requires support for %d DUN bytes.",
+			     fscrypt_modes[fscrypt_mode_num].ivsize, dun_bytes);
+		return -EOPNOTSUPP;
+	}
+
+	crypto_mode = fscrypt_modes[fscrypt_mode_num].blk_crypto_mode;
+
+	err = fscrypt_metadata_get_key_from_id(
+					FSCRYPT_KEY_DESC_PREFIX,
+					key_desc_hex,
+					fscrypt_modes[fscrypt_mode_num].keysize,
+					raw_key);
+	if (err)
+		goto out;
+
+	sb->s_metadata_key = kzalloc(sizeof(*sb->s_metadata_key), GFP_NOFS);
+	if (!sb->s_metadata_key) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	err = blk_crypto_init_key(sb->s_metadata_key, raw_key, crypto_mode,
+				  dun_bytes, sb->s_blocksize);
+	if (err)
+		goto out_free_key;
+
+	err = blk_crypto_start_using_key(sb->s_metadata_key,
+					 bdev_get_queue(sb->s_bdev));
+	if (err)
+		goto out_free_key;
+
+	goto out;
+out_free_key:
+	fscrypt_free_metadata_encryption(sb);
+out:
+	memzero_explicit(raw_key, sizeof(raw_key));
+	return err;
+}
+
+/**
+ * fscrypt_metadata_crypt_prepare_all_devices() - prepare all devices used by
+ *					the filesystem for metadata encryption.
+ * @sb: The super_block whose devices to prepare
+ *
+ * This function should be called when the filesystem has determined all its
+ * devices. This might happen only after some initial setup, which is why
+ * this is a separate function from fscrypt_setup_metadata_encryption().
+ *
+ * Return: 0 on success, negative on error.
+ */
+int fscrypt_metadata_crypt_prepare_all_devices(struct super_block *sb)
+{
+	int num_devices;
+	int i;
+	struct request_queue *q;
+
+	if (!sb->s_metadata_key)
+		return 0;
+
+	num_devices = fscrypt_get_num_devices(sb);
+	for (i = 0; i < num_devices; i++) {
+		q = fscrypt_get_device(sb, i);
+		if (!q || blk_crypto_start_using_key(sb->s_metadata_key, q))
+			return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+/**
+ * fscrypt_free_metadata_encryption() - free metadata encryption fields in
+ *					super_block.
+ * @sb: The super_block to free metatdata encryption fields from
+ */
+void fscrypt_free_metadata_encryption(struct super_block *sb)
+{
+	int num_devices;
+	int i;
+	struct request_queue *q;
+
+	if (!sb->s_metadata_key)
+		return;
+
+	num_devices = fscrypt_get_num_devices(sb);
+
+	for (i = 0; i < num_devices; i++) {
+		q = fscrypt_get_device(sb, i);
+		if (WARN_ON(!q))
+			continue;
+		blk_crypto_evict_key(q, sb->s_metadata_key);
+	}
+
+	memzero_explicit(sb->s_metadata_key, sizeof(*sb->s_metadata_key));
+	kzfree(sb->s_metadata_key);
+	sb->s_metadata_key = NULL;
+}
+
+/**
+ * fscrypt_metadata_crypt_bio() - Add metadata encryption context to bio.
+ *
+ * @bio: The bio to add the encryption context to
+ * @lblk: The logical block number within the filesystem at which this bio
+ *	  starts reading/writing data.
+ * @sb: The superblock of the filesystem
+ * @gfp_mask: gfp_mask for bio_crypt_context allocation
+ */
+void fscrypt_metadata_crypt_bio(struct bio *bio, u64 lblk,
+				struct super_block *sb, gfp_t gfp_mask)
+{
+	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE] = { 0 };
+
+	if (!sb->s_metadata_key)
+		return;
+
+	dun[0] = lblk;
+	bio_crypt_set_ctx(bio, sb->s_metadata_key, dun, gfp_mask);
+}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7519ae003a08..aba3b0e2d56f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1438,6 +1438,9 @@  struct super_block {
 	const struct fscrypt_operations	*s_cop;
 	struct key		*s_master_keys; /* master crypto keys in use */
 #endif
+#ifdef CONFIG_FS_ENCRYPTION_METADATA
+	struct blk_crypto_key	*s_metadata_key;
+#endif
 #ifdef CONFIG_FS_VERITY
 	const struct fsverity_operations *s_vop;
 #endif
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index d835fd19a20a..f7cdc8627984 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -594,6 +594,53 @@  static inline bool fscrypt_mergeable_bio_bh(struct bio *bio,
 }
 #endif /* !CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
 
+/* metadata_crypt.c */
+#ifdef CONFIG_FS_ENCRYPTION_METADATA
+
+int fscrypt_setup_metadata_encryption(struct super_block *sb,
+				      char *key_desc_hex,
+				      int fscrypt_mode_num);
+
+int fscrypt_metadata_crypt_prepare_all_devices(struct super_block *sb);
+
+void fscrypt_free_metadata_encryption(struct super_block *sb);
+
+void fscrypt_metadata_crypt_bio(struct bio *bio, u64 lblk,
+				struct super_block *sb, gfp_t gfp_mask);
+
+static inline bool fscrypt_metadata_crypted(struct super_block *sb)
+{
+	return sb->s_metadata_key;
+}
+
+#else /* CONFIG_FS_ENCRYPTION_METADATA */
+
+static inline int fscrypt_setup_metadata_encryption(struct super_block *sb,
+						    char *key_desc_hex,
+						    int fscrypt_mode_num)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int
+fscrypt_metadata_crypt_prepare_all_devices(struct super_block *sb)
+{
+	return 0;
+}
+
+static inline void fscrypt_free_metadata_encryption(struct super_block *sb) { }
+
+static inline void fscrypt_metadata_crypt_bio(struct bio *bio, u64 lblk,
+					      struct super_block *sb,
+					      gfp_t gfp_mask) { }
+
+static inline bool fscrypt_metadata_crypted(struct super_block *sb)
+{
+	return false;
+}
+
+#endif /* CONFIG_FS_ENCRYPTION_METADATA */
+
 /**
  * fscrypt_inode_uses_inline_crypto() - test whether an inode uses inline
  *					encryption