[PATCH v2 0/5] btrfs: support fsverity

[PATCH v2 0/5] btrfs: support fsverity

[Boris Burkov]

This patchset provides support for fsverity in btrfs.

At a high level, we store the verity descriptor and Merkle tree data
in the file system btree with the file's inode as the objectid, and
direct reads/writes to those items to implement the generic fsverity
interface required by fs/verity/.

The first patch is a preparatory patch which adds a notion of
compat_flags to the btrfs_inode and inode_item in order to allow
enabling verity on a file without making the file system unmountable for
older kernels. (It runs afoul of the leaf corruption check otherwise)

The second patch is the bulk of the fsverity implementation. It
implements the fsverity interface and adds verity checks for the typical
file reading case.

The third patch cleans up the corner cases in readpage, covering inline
extents, preallocated extents, and holes.

The fourth patch handles direct io of a veritied file by falling back to
buffered io.

The fifth patch handles crashes mid-verity enable via orphan items

changes for v2:
Patch 1: Unchanged.
Patch 2: Return EFBIG if Merkle data past s_maxbytes. Added special
descriptor item for encryption and to handle ERANGE case for
get_verity_descriptor. Improved function comments. Rebased onto subpage
read patches -- modified end_page_read to do verity check before marking
the page uptodate. Changed from full compat to ro_compat; merged sysfs
feature here.
Patch 3: Rebased onto subpage read patches.
Patch 4: Unchanged.
Patch 5: Used to be sysfs feature, now a new patch that handles orphaned
verity data.

Boris Burkov (4):
  btrfs: add compat_flags to btrfs_inode_item
  btrfs: check verity for reads of inline extents and holes
  btrfs: fallback to buffered io for verity files
  btrfs: verity metadata orphan items

Chris Mason (1):
  btrfs: initial fsverity support

 fs/btrfs/Makefile               |   1 +
 fs/btrfs/btrfs_inode.h          |   2 +
 fs/btrfs/ctree.h                |  25 +-
 fs/btrfs/delayed-inode.c        |   2 +
 fs/btrfs/extent_io.c            |  53 +--
 fs/btrfs/file.c                 |   9 +
 fs/btrfs/inode.c                |  25 +-
 fs/btrfs/ioctl.c                |  21 +-
 fs/btrfs/super.c                |   1 +
 fs/btrfs/sysfs.c                |   6 +
 fs/btrfs/tree-log.c             |   1 +
 fs/btrfs/verity.c               | 658 ++++++++++++++++++++++++++++++++
 include/uapi/linux/btrfs.h      |   2 +-
 include/uapi/linux/btrfs_tree.h |  22 +-
 14 files changed, 792 insertions(+), 36 deletions(-)
 create mode 100644 fs/btrfs/verity.c

-- 
2.24.1

[PATCH v2 1/5] btrfs: add compat_flags to btrfs_inode_item

[Boris Burkov]

The tree checker currently rejects unrecognized flags when it reads
btrfs_inode_item. Practically, this means that adding a new flag makes
the change backwards incompatible if the flag is ever set on a file.

Take up one of the 4 reserved u64 fields in the btrfs_inode_item as a
new "compat_flags". These flags are zero on inode creation in btrfs and
mkfs and are ignored by an older kernel, so it should be safe to use
them in this way.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/btrfs_inode.h          | 1 +
 fs/btrfs/ctree.h                | 2 ++
 fs/btrfs/delayed-inode.c        | 2 ++
 fs/btrfs/inode.c                | 3 +++
 fs/btrfs/ioctl.c                | 7 ++++---
 fs/btrfs/tree-log.c             | 1 +
 include/uapi/linux/btrfs_tree.h | 7 ++++++-
 7 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 28e202e89660..8b95932f25a8 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -191,6 +191,7 @@ struct btrfs_inode {
 
 	/* flags field from the on disk inode */
 	u32 flags;
+	u64 compat_flags;
 
 	/*
 	 * Counters to keep track of the number of extent item's we may use due
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 40ec3393d2a1..e65df997a2c6 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1761,6 +1761,7 @@ BTRFS_SETGET_FUNCS(inode_gid, struct btrfs_inode_item, gid, 32);
 BTRFS_SETGET_FUNCS(inode_mode, struct btrfs_inode_item, mode, 32);
 BTRFS_SETGET_FUNCS(inode_rdev, struct btrfs_inode_item, rdev, 64);
 BTRFS_SETGET_FUNCS(inode_flags, struct btrfs_inode_item, flags, 64);
+BTRFS_SETGET_FUNCS(inode_compat_flags, struct btrfs_inode_item, compat_flags, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_inode_generation, struct btrfs_inode_item,
 			 generation, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_inode_sequence, struct btrfs_inode_item,
@@ -1778,6 +1779,7 @@ BTRFS_SETGET_STACK_FUNCS(stack_inode_gid, struct btrfs_inode_item, gid, 32);
 BTRFS_SETGET_STACK_FUNCS(stack_inode_mode, struct btrfs_inode_item, mode, 32);
 BTRFS_SETGET_STACK_FUNCS(stack_inode_rdev, struct btrfs_inode_item, rdev, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_inode_flags, struct btrfs_inode_item, flags, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_inode_compat_flags, struct btrfs_inode_item, compat_flags, 64);
 BTRFS_SETGET_FUNCS(timespec_sec, struct btrfs_timespec, sec, 64);
 BTRFS_SETGET_FUNCS(timespec_nsec, struct btrfs_timespec, nsec, 32);
 BTRFS_SETGET_STACK_FUNCS(stack_timespec_sec, struct btrfs_timespec, sec, 64);
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index ec0b50b8c5d6..6ea9d27b9c9d 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1733,6 +1733,7 @@ static void fill_stack_inode_item(struct btrfs_trans_handle *trans,
 	btrfs_set_stack_inode_transid(inode_item, trans->transid);
 	btrfs_set_stack_inode_rdev(inode_item, inode->i_rdev);
 	btrfs_set_stack_inode_flags(inode_item, BTRFS_I(inode)->flags);
+	btrfs_set_stack_inode_compat_flags(inode_item, BTRFS_I(inode)->compat_flags);
 	btrfs_set_stack_inode_block_group(inode_item, 0);
 
 	btrfs_set_stack_timespec_sec(&inode_item->atime,
@@ -1791,6 +1792,7 @@ int btrfs_fill_inode(struct inode *inode, u32 *rdev)
 	inode->i_rdev = 0;
 	*rdev = btrfs_stack_inode_rdev(inode_item);
 	BTRFS_I(inode)->flags = btrfs_stack_inode_flags(inode_item);
+	BTRFS_I(inode)->compat_flags = btrfs_stack_inode_compat_flags(inode_item);
 
 	inode->i_atime.tv_sec = btrfs_stack_timespec_sec(&inode_item->atime);
 	inode->i_atime.tv_nsec = btrfs_stack_timespec_nsec(&inode_item->atime);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4f2f1e932751..4529e974c582 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3627,6 +3627,7 @@ static int btrfs_read_locked_inode(struct inode *inode,
 
 	BTRFS_I(inode)->index_cnt = (u64)-1;
 	BTRFS_I(inode)->flags = btrfs_inode_flags(leaf, inode_item);
+	BTRFS_I(inode)->compat_flags = btrfs_inode_compat_flags(leaf, inode_item);
 
 cache_index:
 	/*
@@ -3793,6 +3794,7 @@ static void fill_inode_item(struct btrfs_trans_handle *trans,
 	btrfs_set_token_inode_transid(&token, item, trans->transid);
 	btrfs_set_token_inode_rdev(&token, item, inode->i_rdev);
 	btrfs_set_token_inode_flags(&token, item, BTRFS_I(inode)->flags);
+	btrfs_set_token_inode_compat_flags(&token, item, BTRFS_I(inode)->compat_flags);
 	btrfs_set_token_inode_block_group(&token, item, 0);
 }
 
@@ -8844,6 +8846,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 	ei->defrag_bytes = 0;
 	ei->disk_i_size = 0;
 	ei->flags = 0;
+	ei->compat_flags = 0;
 	ei->csum_bytes = 0;
 	ei->index_cnt = (u64)-1;
 	ei->dir_index = 0;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a8c60d46d19c..d3fb065312f5 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -102,8 +102,9 @@ static unsigned int btrfs_mask_fsflags_for_type(struct inode *inode,
  * Export internal inode flags to the format expected by the FS_IOC_GETFLAGS
  * ioctl.
  */
-static unsigned int btrfs_inode_flags_to_fsflags(unsigned int flags)
+static unsigned int btrfs_inode_flags_to_fsflags(struct btrfs_inode *binode)
 {
+	unsigned int flags = binode->flags;
 	unsigned int iflags = 0;
 
 	if (flags & BTRFS_INODE_SYNC)
@@ -156,7 +157,7 @@ void btrfs_sync_inode_flags_to_i_flags(struct inode *inode)
 static int btrfs_ioctl_getflags(struct file *file, void __user *arg)
 {
 	struct btrfs_inode *binode = BTRFS_I(file_inode(file));
-	unsigned int flags = btrfs_inode_flags_to_fsflags(binode->flags);
+	unsigned int flags = btrfs_inode_flags_to_fsflags(binode);
 
 	if (copy_to_user(arg, &flags, sizeof(flags)))
 		return -EFAULT;
@@ -228,7 +229,7 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 
 	inode_lock(inode);
 	fsflags = btrfs_mask_fsflags_for_type(inode, fsflags);
-	old_fsflags = btrfs_inode_flags_to_fsflags(binode->flags);
+	old_fsflags = btrfs_inode_flags_to_fsflags(binode);
 
 	ret = vfs_ioc_setflags_prepare(inode, old_fsflags, fsflags);
 	if (ret)
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 2f1acc9aea9e..c436b4517452 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3942,6 +3942,7 @@ static void fill_inode_item(struct btrfs_trans_handle *trans,
 	btrfs_set_token_inode_transid(&token, item, trans->transid);
 	btrfs_set_token_inode_rdev(&token, item, inode->i_rdev);
 	btrfs_set_token_inode_flags(&token, item, BTRFS_I(inode)->flags);
+	btrfs_set_token_inode_compat_flags(&token, item, BTRFS_I(inode)->compat_flags);
 	btrfs_set_token_inode_block_group(&token, item, 0);
 }
 
diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index 58d7cff9afb1..ae25280316bd 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -574,11 +574,16 @@ struct btrfs_inode_item {
 	/* modification sequence number for NFS */
 	__le64 sequence;
 
+	/*
+	 * flags which aren't checked for corruption at mount
+	 * and can be added in a backwards compatible way
+	 */
+	__le64 compat_flags;
 	/*
 	 * a little future expansion, for more than this we can
 	 * just grow the inode item and version it
 	 */
-	__le64 reserved[4];
+	__le64 reserved[3];
 	struct btrfs_timespec atime;
 	struct btrfs_timespec ctime;
 	struct btrfs_timespec mtime;
-- 
2.24.1

Re: [PATCH v2 1/5] btrfs: add compat_flags to btrfs_inode_item

[Eric Biggers]

On Fri, Mar 05, 2021 at 11:26:29AM -0800, Boris Burkov wrote:
> The tree checker currently rejects unrecognized flags when it reads
> btrfs_inode_item. Practically, this means that adding a new flag makes
> the change backwards incompatible if the flag is ever set on a file.
> 
> Take up one of the 4 reserved u64 fields in the btrfs_inode_item as a
> new "compat_flags". These flags are zero on inode creation in btrfs and
> mkfs and are ignored by an older kernel, so it should be safe to use
> them in this way.
> 
> Signed-off-by: Boris Burkov <boris@bur.io>

How does this interact with the RO_COMPAT filesystem flag which is also being
added?

- Eric

Re: [PATCH v2 1/5] btrfs: add compat_flags to btrfs_inode_item

[Boris Burkov]

On Mon, Mar 15, 2021 at 04:07:24PM -0700, Eric Biggers wrote:
> On Fri, Mar 05, 2021 at 11:26:29AM -0800, Boris Burkov wrote:
> > The tree checker currently rejects unrecognized flags when it reads
> > btrfs_inode_item. Practically, this means that adding a new flag makes
> > the change backwards incompatible if the flag is ever set on a file.
> > 
> > Take up one of the 4 reserved u64 fields in the btrfs_inode_item as a
> > new "compat_flags". These flags are zero on inode creation in btrfs and
> > mkfs and are ignored by an older kernel, so it should be safe to use
> > them in this way.
> > 
> > Signed-off-by: Boris Burkov <boris@bur.io>
> 
> How does this interact with the RO_COMPAT filesystem flag which is also being
> added?
> 
> - Eric

This allows us to mount at all -- without it, when mounting on an older
system, the logic in fs/btrfs/tree-checker.c would see an unexpected
inode flag value and reject the filesystem entirely.

The RO_COMPAT flag represents the decision to mount RO rather than RW
when a verity file is present (though it suffers from the fact that it
gets set on verity enable, but not unset when the last verity file is
deleted)

I'm now thinking that ro_compat inode flags might be an interesting
option where the tree-checker could indicate we have to mount read only
if it sees an unrecognized value.

[PATCH v2 2/5] btrfs: initial fsverity support

[Boris Burkov]

From: Chris Mason <clm@fb.com>

Add support for fsverity in btrfs. To support the generic interface in
fs/verity, we add two new item types in the fs tree for inodes with
verity enabled. One stores the per-file verity descriptor and the other
stores the Merkle tree data itself.

Verity checking is done at the end of IOs to ensure each page is checked
before it is marked uptodate.

Verity relies on PageChecked for the Merkle tree data itself to avoid
re-walking up shared paths in the tree. For this reason, we need to
cache the Merkle tree data. Since the file is immutable after verity is
turned on, we can cache it at an index past EOF.

Use the new inode compat_flags to store verity on the inode item, so
that we can enable verity on a file, then rollback to an older kernel
and still mount the file system and read the file. Since we can't safely
write the file anymore without ruining the invariants of the Merkle
tree, we mark a ro_compat flag on the file system when a file has verity
enabled.

Signed-off-by: Chris Mason <clm@fb.com>
---
 fs/btrfs/Makefile               |   1 +
 fs/btrfs/btrfs_inode.h          |   1 +
 fs/btrfs/ctree.h                |  23 +-
 fs/btrfs/extent_io.c            |  27 +-
 fs/btrfs/file.c                 |   6 +
 fs/btrfs/inode.c                |   7 +
 fs/btrfs/ioctl.c                |  14 +-
 fs/btrfs/super.c                |   1 +
 fs/btrfs/sysfs.c                |   6 +
 fs/btrfs/verity.c               | 598 ++++++++++++++++++++++++++++++++
 include/uapi/linux/btrfs.h      |   2 +-
 include/uapi/linux/btrfs_tree.h |  15 +
 12 files changed, 690 insertions(+), 11 deletions(-)
 create mode 100644 fs/btrfs/verity.c

diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index b634c42115ea..ff719d2bba1a 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -34,6 +34,7 @@ btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
 btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
 btrfs-$(CONFIG_BTRFS_FS_REF_VERIFY) += ref-verify.o
 btrfs-$(CONFIG_BLK_DEV_ZONED) += zoned.o
+btrfs-$(CONFIG_FS_VERITY) += verity.o
 
 btrfs-$(CONFIG_BTRFS_FS_RUN_SANITY_TESTS) += tests/free-space-tests.o \
 	tests/extent-buffer-tests.o tests/btrfs-tests.o \
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 8b95932f25a8..c0b0537bd50e 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -51,6 +51,7 @@ enum {
 	 * the file range, inode's io_tree).
 	 */
 	BTRFS_INODE_NO_DELALLOC_FLUSH,
+	BTRFS_INODE_VERITY_IN_PROGRESS,
 };
 
 /* in memory btrfs inode */
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e65df997a2c6..f73ba7794dda 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -279,9 +279,10 @@ struct btrfs_super_block {
 #define BTRFS_FEATURE_COMPAT_SAFE_SET		0ULL
 #define BTRFS_FEATURE_COMPAT_SAFE_CLEAR		0ULL
 
-#define BTRFS_FEATURE_COMPAT_RO_SUPP			\
-	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |	\
-	 BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID)
+#define BTRFS_FEATURE_COMPAT_RO_SUPP				\
+	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |		\
+	 BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID |	\
+	 BTRFS_FEATURE_COMPAT_RO_VERITY)
 
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_SET	0ULL
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_CLEAR	0ULL
@@ -1480,6 +1481,11 @@ do {                                                                   \
 	 BTRFS_INODE_COMPRESS |						\
 	 BTRFS_INODE_ROOT_ITEM_INIT)
 
+/*
+ * Inode compat flags
+ */
+#define BTRFS_INODE_VERITY		(1 << 0)
+
 struct btrfs_map_token {
 	struct extent_buffer *eb;
 	char *kaddr;
@@ -3735,6 +3741,17 @@ static inline int btrfs_defrag_cancelled(struct btrfs_fs_info *fs_info)
 
 #define in_range(b, first, len) ((b) >= (first) && (b) < (first) + (len))
 
+/* verity.c */
+extern const struct fsverity_operations btrfs_verityops;
+int btrfs_drop_verity_items(struct btrfs_inode *inode);
+BTRFS_SETGET_FUNCS(verity_descriptor_encryption, struct btrfs_verity_descriptor_item,
+		   encryption, 8);
+BTRFS_SETGET_FUNCS(verity_descriptor_size, struct btrfs_verity_descriptor_item, size, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_verity_descriptor_encryption, struct btrfs_verity_descriptor_item,
+			 encryption, 8);
+BTRFS_SETGET_STACK_FUNCS(stack_verity_descriptor_size, struct btrfs_verity_descriptor_item,
+			 size, 64);
+
 /* Sanity test specific functions */
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 void btrfs_test_destroy_inode(struct inode *inode);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 4dfb3ead1175..0d6f8b33830f 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -13,6 +13,7 @@
 #include <linux/pagevec.h>
 #include <linux/prefetch.h>
 #include <linux/cleancache.h>
+#include <linux/fsverity.h>
 #include "extent_io.h"
 #include "extent-io-tree.h"
 #include "extent_map.h"
@@ -2861,15 +2862,28 @@ static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
 	btrfs_subpage_start_reader(fs_info, page, page_offset(page), PAGE_SIZE);
 }
 
-static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
+static int end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
 {
-	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	int ret = 0;
+	struct inode *inode = page->mapping->host;
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 
 	ASSERT(page_offset(page) <= start &&
 		start + len <= page_offset(page) + PAGE_SIZE);
 
 	if (uptodate) {
-		btrfs_page_set_uptodate(fs_info, page, start, len);
+		/*
+		 * buffered reads of a file with page alignment will issue a
+		 * 0 length read for one page past the end of file, so we must
+		 * explicitly skip checking verity on that page of zeros.
+		 */
+		if (!PageError(page) && !PageUptodate(page) &&
+		    start < i_size_read(inode) &&
+		    fsverity_active(inode) &&
+		    fsverity_verify_page(page) != true)
+			ret = -EIO;
+		else
+			btrfs_page_set_uptodate(fs_info, page, start, len);
 	} else {
 		btrfs_page_clear_uptodate(fs_info, page, start, len);
 		btrfs_page_set_error(fs_info, page, start, len);
@@ -2877,12 +2891,13 @@ static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
 
 	if (fs_info->sectorsize == PAGE_SIZE)
 		unlock_page(page);
-	else if (is_data_inode(page->mapping->host))
+	else if (is_data_inode(inode))
 		/*
 		 * For subpage data, unlock the page if we're the last reader.
 		 * For subpage metadata, page lock is not utilized for read.
 		 */
 		btrfs_subpage_end_reader(fs_info, page, start, len);
+	return ret;
 }
 
 /*
@@ -3019,7 +3034,9 @@ static void end_bio_extent_readpage(struct bio *bio)
 		bio_offset += len;
 
 		/* Update page status and unlock */
-		end_page_read(page, uptodate, start, len);
+		ret = end_page_read(page, uptodate, start, len);
+		if (ret)
+			uptodate = 0;
 		endio_readpage_release_extent(&processed, BTRFS_I(inode),
 					      start, end, uptodate);
 	}
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 2c282664c4b8..75f1406021e5 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -16,6 +16,7 @@
 #include <linux/btrfs.h>
 #include <linux/uio.h>
 #include <linux/iversion.h>
+#include <linux/fsverity.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -3588,7 +3589,12 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
 
 static int btrfs_file_open(struct inode *inode, struct file *filp)
 {
+	int ret;
 	filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC;
+
+	ret = fsverity_file_open(inode, filp);
+	if (ret)
+		return ret;
 	return generic_file_open(inode, filp);
 }
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4529e974c582..9291f6633bc6 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -32,6 +32,7 @@
 #include <linux/sched/mm.h>
 #include <linux/iomap.h>
 #include <asm/unaligned.h>
+#include <linux/fsverity.h>
 #include "misc.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -5399,7 +5400,9 @@ void btrfs_evict_inode(struct inode *inode)
 
 	trace_btrfs_inode_evict(inode);
 
+
 	if (!root) {
+		fsverity_cleanup_inode(inode);
 		clear_inode(inode);
 		return;
 	}
@@ -5482,6 +5485,7 @@ void btrfs_evict_inode(struct inode *inode)
 	 * to retry these periodically in the future.
 	 */
 	btrfs_remove_delayed_node(BTRFS_I(inode));
+	fsverity_cleanup_inode(inode);
 	clear_inode(inode);
 }
 
@@ -9026,6 +9030,7 @@ static int btrfs_getattr(const struct path *path, struct kstat *stat,
 	struct inode *inode = d_inode(path->dentry);
 	u32 blocksize = inode->i_sb->s_blocksize;
 	u32 bi_flags = BTRFS_I(inode)->flags;
+	u32 bi_compat_flags = BTRFS_I(inode)->compat_flags;
 
 	stat->result_mask |= STATX_BTIME;
 	stat->btime.tv_sec = BTRFS_I(inode)->i_otime.tv_sec;
@@ -9038,6 +9043,8 @@ static int btrfs_getattr(const struct path *path, struct kstat *stat,
 		stat->attributes |= STATX_ATTR_IMMUTABLE;
 	if (bi_flags & BTRFS_INODE_NODUMP)
 		stat->attributes |= STATX_ATTR_NODUMP;
+	if (bi_compat_flags & BTRFS_INODE_VERITY)
+		stat->attributes |= STATX_ATTR_VERITY;
 
 	stat->attributes_mask |= (STATX_ATTR_APPEND |
 				  STATX_ATTR_COMPRESSED |
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d3fb065312f5..cf91d8f0d479 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -26,6 +26,7 @@
 #include <linux/btrfs.h>
 #include <linux/uaccess.h>
 #include <linux/iversion.h>
+#include <linux/fsverity.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "export.h"
@@ -105,6 +106,7 @@ static unsigned int btrfs_mask_fsflags_for_type(struct inode *inode,
 static unsigned int btrfs_inode_flags_to_fsflags(struct btrfs_inode *binode)
 {
 	unsigned int flags = binode->flags;
+	unsigned int compat_flags = binode->compat_flags;
 	unsigned int iflags = 0;
 
 	if (flags & BTRFS_INODE_SYNC)
@@ -121,6 +123,8 @@ static unsigned int btrfs_inode_flags_to_fsflags(struct btrfs_inode *binode)
 		iflags |= FS_DIRSYNC_FL;
 	if (flags & BTRFS_INODE_NODATACOW)
 		iflags |= FS_NOCOW_FL;
+	if (compat_flags & BTRFS_INODE_VERITY)
+		iflags |= FS_VERITY_FL;
 
 	if (flags & BTRFS_INODE_NOCOMPRESS)
 		iflags |= FS_NOCOMP_FL;
@@ -148,10 +152,12 @@ void btrfs_sync_inode_flags_to_i_flags(struct inode *inode)
 		new_fl |= S_NOATIME;
 	if (binode->flags & BTRFS_INODE_DIRSYNC)
 		new_fl |= S_DIRSYNC;
+	if (binode->compat_flags & BTRFS_INODE_VERITY)
+		new_fl |= S_VERITY;
 
 	set_mask_bits(&inode->i_flags,
-		      S_SYNC | S_APPEND | S_IMMUTABLE | S_NOATIME | S_DIRSYNC,
-		      new_fl);
+		      S_SYNC | S_APPEND | S_IMMUTABLE | S_NOATIME | S_DIRSYNC |
+		      S_VERITY, new_fl);
 }
 
 static int btrfs_ioctl_getflags(struct file *file, void __user *arg)
@@ -5035,6 +5041,10 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_get_subvol_rootref(file, argp);
 	case BTRFS_IOC_INO_LOOKUP_USER:
 		return btrfs_ioctl_ino_lookup_user(file, argp);
+	case FS_IOC_ENABLE_VERITY:
+		return fsverity_ioctl_enable(file, (const void __user *)argp);
+	case FS_IOC_MEASURE_VERITY:
+		return fsverity_ioctl_measure(file, argp);
 	}
 
 	return -ENOTTY;
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f8435641b912..be7dfde7e4cf 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1339,6 +1339,7 @@ static int btrfs_fill_super(struct super_block *sb,
 	sb->s_op = &btrfs_super_ops;
 	sb->s_d_op = &btrfs_dentry_operations;
 	sb->s_export_op = &btrfs_export_ops;
+	sb->s_vop = &btrfs_verityops;
 	sb->s_xattr = btrfs_xattr_handlers;
 	sb->s_time_gran = 1;
 #ifdef CONFIG_BTRFS_FS_POSIX_ACL
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 6eb1c50fa98c..e8de0055c61e 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -267,6 +267,9 @@ BTRFS_FEAT_ATTR_INCOMPAT(raid1c34, RAID1C34);
 #ifdef CONFIG_BTRFS_DEBUG
 BTRFS_FEAT_ATTR_INCOMPAT(zoned, ZONED);
 #endif
+#ifdef CONFIG_FS_VERITY
+BTRFS_FEAT_ATTR_COMPAT_RO(verity, VERITY);
+#endif
 
 static struct attribute *btrfs_supported_feature_attrs[] = {
 	BTRFS_FEAT_ATTR_PTR(mixed_backref),
@@ -284,6 +287,9 @@ static struct attribute *btrfs_supported_feature_attrs[] = {
 	BTRFS_FEAT_ATTR_PTR(raid1c34),
 #ifdef CONFIG_BTRFS_DEBUG
 	BTRFS_FEAT_ATTR_PTR(zoned),
+#endif
+#ifdef CONFIG_FS_VERITY
+	BTRFS_FEAT_ATTR_PTR(verity),
 #endif
 	NULL
 };
diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
new file mode 100644
index 000000000000..648bda5a3716
--- /dev/null
+++ b/fs/btrfs/verity.c
@@ -0,0 +1,598 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Facebook.  All rights reserved.
+ */
+
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/rwsem.h>
+#include <linux/xattr.h>
+#include <linux/security.h>
+#include <linux/posix_acl_xattr.h>
+#include <linux/iversion.h>
+#include <linux/fsverity.h>
+#include <linux/sched/mm.h>
+#include "ctree.h"
+#include "btrfs_inode.h"
+#include "transaction.h"
+#include "disk-io.h"
+#include "locking.h"
+
+/*
+ * Just like ext4, we cache the merkle tree in pages after EOF in the page
+ * cache.  Unlike ext4, we're storing these in dedicated btree items and
+ * not just shoving them after EOF in the file.  This means we'll need to
+ * do extra work to encrypt them once encryption is supported in btrfs,
+ * but btrfs has a lot of careful code around i_size and it seems better
+ * to make a new key type than try and adjust all of our expectations
+ * for i_size.
+ *
+ * fs verity items are stored under two different key types on disk.
+ *
+ * The descriptor items:
+ * [ inode objectid, BTRFS_VERITY_DESC_ITEM_KEY, offset ]
+ *
+ * At offset 0, we store a btrfs_verity_descriptor_item which tracks the
+ * size of the descriptor item and some extra data for encryption.
+ * Starting at offset 1, these hold the generic fs verity descriptor.
+ * These are opaque to btrfs, we just read and write them as a blob for
+ * the higher level verity code.  The most common size for this is 256 bytes.
+ *
+ * The merkle tree items:
+ * [ inode objectid, BTRFS_VERITY_MERKLE_ITEM_KEY, offset ]
+ *
+ * These also start at offset 0, and correspond to the merkle tree bytes.
+ * So when fsverity asks for page 0 of the merkle tree, we pull up one page
+ * starting at offset 0 for this key type.  These are also opaque to btrfs,
+ * we're blindly storing whatever fsverity sends down.
+ *
+ * This file is just reading and writing the various items whenever
+ * fsverity needs us to.
+ */
+
+/*
+ * Drop all the items for this inode with this key_type.
+ * @inode: The inode to drop items for
+ * @key_type: The type of items to drop (VERITY_DESC_ITEM or
+ *            VERITY_MERKLE_ITEM)
+ *
+ * Before doing a verity enable we cleanup any existing verity items.
+ *
+ * This is also used to clean up if a verity enable failed half way
+ * through.
+ *
+ * Returns 0 on success, negative error code on failure.
+ */
+static int drop_verity_items(struct btrfs_inode *inode, u8 key_type)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *root = inode->root;
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	while (1) {
+		trans = btrfs_start_transaction(root, 1);
+		if (IS_ERR(trans)) {
+			ret = PTR_ERR(trans);
+			goto out;
+		}
+
+		/*
+		 * walk backwards through all the items until we find one
+		 * that isn't from our key type or objectid
+		 */
+		key.objectid = btrfs_ino(inode);
+		key.offset = (u64)-1;
+		key.type = key_type;
+
+		ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+		if (ret > 0) {
+			ret = 0;
+			/* no more keys of this type, we're done */
+			if (path->slots[0] == 0)
+				break;
+			path->slots[0]--;
+		} else if (ret < 0) {
+			break;
+		}
+
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+
+		/* no more keys of this type, we're done */
+		if (key.objectid != btrfs_ino(inode) || key.type != key_type)
+			break;
+
+		/*
+		 * this shouldn't be a performance sensitive function because
+		 * it's not used as part of truncate.  If it ever becomes
+		 * perf sensitive, change this to walk forward and bulk delete
+		 * items
+		 */
+		ret = btrfs_del_items(trans, root, path,
+				      path->slots[0], 1);
+		btrfs_release_path(path);
+		btrfs_end_transaction(trans);
+
+		if (ret)
+			goto out;
+	}
+
+	btrfs_end_transaction(trans);
+out:
+	btrfs_free_path(path);
+	return ret;
+
+}
+
+/*
+ * Insert and write inode items with a given key type and offset.
+ * @inode: The inode to insert for.
+ * @key_type: The key type to insert.
+ * @offset: The item offset to insert at.
+ * @src: Source data to write.
+ * @len: Length of source data to write.
+ * @max_item_size: Break up the write into items of this size at most.
+ *                 Useful for small leaf size file systems.
+ *
+ * Write len bytes from src into items of up to max_item_size length.
+ * The inserted items will have key <ino, key_type, offset + off> where
+ * off is consecutively increasing from 0 up to the last item ending at
+ * offset + len.
+ *
+ * Returns 0 on success and a negative error code on failure.
+ */
+static int write_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
+			   const char *src, u64 len)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_path *path;
+	struct btrfs_root *root = inode->root;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	u64 orig_len = len;
+	u64 copied = 0;
+	unsigned long copy_bytes;
+	unsigned long src_offset = 0;
+	void *data;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	while (len > 0) {
+		trans = btrfs_start_transaction(root, 1);
+		if (IS_ERR(trans)) {
+			ret = PTR_ERR(trans);
+			break;
+		}
+
+		key.objectid = btrfs_ino(inode);
+		key.offset = offset;
+		key.type = key_type;
+
+		/*
+		 * insert 1K at a time mostly to be friendly for smaller
+		 * leaf size filesystems
+		 */
+		copy_bytes = min_t(u64, len, 1024);
+
+		ret = btrfs_insert_empty_item(trans, root, path, &key, copy_bytes);
+		if (ret) {
+			btrfs_end_transaction(trans);
+			break;
+		}
+
+		leaf = path->nodes[0];
+
+		data = btrfs_item_ptr(leaf, path->slots[0], void);
+		write_extent_buffer(leaf, src + src_offset,
+				    (unsigned long)data, copy_bytes);
+		offset += copy_bytes;
+		src_offset += copy_bytes;
+		len -= copy_bytes;
+		copied += copy_bytes;
+
+		btrfs_release_path(path);
+		btrfs_end_transaction(trans);
+	}
+
+	btrfs_free_path(path);
+
+	if (!ret && copied != orig_len)
+		ret = -EIO;
+	return ret;
+}
+
+/*
+ * Read inode items of the given key type and offset from the btree.
+ * @inode: The inode to read items of.
+ * @key_type: The key type to read.
+ * @offset: The item offset to read from.
+ * @dest: The buffer to read into. This parameter has slightly tricky
+ *        semantics.  If it is NULL, the function will not do any copying
+ *        and will just return the size of all the items up to len bytes.
+ *        If dest_page is passed, then the function will kmap_atomic the
+ *        page and ignore dest, but it must still be non-NULL to avoid the
+ *        counting-only behavior.
+ * @len: Length in bytes to read.
+ * @dest_page: Copy into this page instead of the dest buffer.
+ *
+ * Helper function to read items from the btree.  This returns the number
+ * of bytes read or < 0 for errors.  We can return short reads if the
+ * items don't exist on disk or aren't big enough to fill the desired length.
+ *
+ * Supports reading into a provided buffer (dest) or into the page cache
+ *
+ * Returns number of bytes read or a negative error code on failure.
+ */
+static ssize_t read_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
+			  char *dest, u64 len, struct page *dest_page)
+{
+	struct btrfs_path *path;
+	struct btrfs_root *root = inode->root;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	u64 item_end;
+	u64 copy_end;
+	u64 copied = 0;
+	u32 copy_offset;
+	unsigned long copy_bytes;
+	unsigned long dest_offset = 0;
+	void *data;
+	char *kaddr = dest;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	if (dest_page)
+		path->reada = READA_FORWARD;
+
+	key.objectid = btrfs_ino(inode);
+	key.offset = offset;
+	key.type = key_type;
+
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0) {
+		goto out;
+	} else if (ret > 0) {
+		ret = 0;
+		if (path->slots[0] == 0)
+			goto out;
+		path->slots[0]--;
+	}
+
+	while (len > 0) {
+		leaf = path->nodes[0];
+		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+		if (key.objectid != btrfs_ino(inode) ||
+		    key.type != key_type)
+			break;
+
+		item_end = btrfs_item_size_nr(leaf, path->slots[0]) + key.offset;
+
+		if (copied > 0) {
+			/*
+			 * once we've copied something, we want all of the items
+			 * to be sequential
+			 */
+			if (key.offset != offset)
+				break;
+		} else {
+			/*
+			 * our initial offset might be in the middle of an
+			 * item.  Make sure it all makes sense
+			 */
+			if (key.offset > offset)
+				break;
+			if (item_end <= offset)
+				break;
+		}
+
+		/* desc = NULL to just sum all the item lengths */
+		if (!dest)
+			copy_end = item_end;
+		else
+			copy_end = min(offset + len, item_end);
+
+		/* number of bytes in this item we want to copy */
+		copy_bytes = copy_end - offset;
+
+		/* offset from the start of item for copying */
+		copy_offset = offset - key.offset;
+
+		if (dest) {
+			if (dest_page)
+				kaddr = kmap_atomic(dest_page);
+
+			data = btrfs_item_ptr(leaf, path->slots[0], void);
+			read_extent_buffer(leaf, kaddr + dest_offset,
+					   (unsigned long)data + copy_offset,
+					   copy_bytes);
+
+			if (dest_page)
+				kunmap_atomic(kaddr);
+		}
+
+		offset += copy_bytes;
+		dest_offset += copy_bytes;
+		len -= copy_bytes;
+		copied += copy_bytes;
+
+		path->slots[0]++;
+		if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+			/*
+			 * we've reached the last slot in this leaf and we need
+			 * to go to the next leaf.
+			 */
+			ret = btrfs_next_leaf(root, path);
+			if (ret < 0) {
+				break;
+			} else if (ret > 0) {
+				ret = 0;
+				break;
+			}
+		}
+	}
+out:
+	btrfs_free_path(path);
+	if (!ret)
+		ret = copied;
+	return ret;
+}
+
+/*
+ * fsverity op that begins enabling verity.
+ * fsverity calls this to ask us to setup the inode for enabling.  We
+ * drop any existing verity items and set the in progress bit.
+ */
+static int btrfs_begin_enable_verity(struct file *filp)
+{
+	struct inode *inode = file_inode(filp);
+	int ret;
+
+	if (test_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags))
+		return -EBUSY;
+
+	/*
+	 * ext4 adds the inode to the orphan list here, presumably because the
+	 * truncate done at orphan processing time will delete partial
+	 * measurements.  TODO: setup orphans
+	 */
+	set_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags);
+	ret = drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY);
+	if (ret)
+		goto err;
+
+	ret = drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY);
+	if (ret)
+		goto err;
+
+	return 0;
+
+err:
+	clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags);
+	return ret;
+
+}
+
+/*
+ * fsverity op that ends enabling verity.
+ * fsverity calls this when it's done with all of the pages in the file
+ * and all of the merkle items have been inserted.  We write the
+ * descriptor and update the inode in the btree to reflect its new life
+ * as a verity file.
+ */
+static int btrfs_end_enable_verity(struct file *filp, const void *desc,
+				  size_t desc_size, u64 merkle_tree_size)
+{
+	struct btrfs_trans_handle *trans;
+	struct inode *inode = file_inode(filp);
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct btrfs_verity_descriptor_item item;
+	int ret;
+
+	if (desc != NULL) {
+		/* write out the descriptor item */
+		memset(&item, 0, sizeof(item));
+		btrfs_set_stack_verity_descriptor_size(&item, desc_size);
+		ret = write_key_bytes(BTRFS_I(inode),
+				      BTRFS_VERITY_DESC_ITEM_KEY, 0,
+				      (const char *)&item, sizeof(item));
+		if (ret)
+			goto out;
+		/* write out the descriptor itself */
+		ret = write_key_bytes(BTRFS_I(inode),
+				      BTRFS_VERITY_DESC_ITEM_KEY, 1,
+				      desc, desc_size);
+		if (ret)
+			goto out;
+
+		/* update our inode flags to include fs verity */
+		trans = btrfs_start_transaction(root, 1);
+		if (IS_ERR(trans)) {
+			ret = PTR_ERR(trans);
+			goto out;
+		}
+		BTRFS_I(inode)->compat_flags |= BTRFS_INODE_VERITY;
+		btrfs_sync_inode_flags_to_i_flags(inode);
+		ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
+		btrfs_end_transaction(trans);
+	}
+
+out:
+	if (desc == NULL || ret) {
+		/* If we failed, drop all the verity items */
+		drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY);
+		drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY);
+	} else
+		btrfs_set_fs_compat_ro(root->fs_info, VERITY);
+	clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags);
+	return ret;
+}
+
+/*
+ * fsverity op that gets the struct fsverity_descriptor.
+ * fsverity does a two pass setup for reading the descriptor, in the first pass
+ * it calls with buf_size = 0 to query the size of the descriptor,
+ * and then in the second pass it actually reads the descriptor off
+ * disk.
+ */
+static int btrfs_get_verity_descriptor(struct inode *inode, void *buf,
+				       size_t buf_size)
+{
+	size_t true_size;
+	ssize_t ret = 0;
+	struct btrfs_verity_descriptor_item item;
+
+	memset(&item, 0, sizeof(item));
+	ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY,
+			     0, (char *)&item, sizeof(item), NULL);
+	if (ret < 0)
+		return ret;
+
+	true_size = btrfs_stack_verity_descriptor_size(&item);
+	if (!buf_size)
+		return true_size;
+	if (buf_size < true_size)
+		return -ERANGE;
+
+	ret = read_key_bytes(BTRFS_I(inode),
+			     BTRFS_VERITY_DESC_ITEM_KEY, 1,
+			     buf, buf_size, NULL);
+	if (ret < 0)
+		return ret;
+	if (ret != buf_size)
+		return -EIO;
+
+	return buf_size;
+}
+
+/*
+ * Helper function for computing cache index for Merkle tree pages
+ * @inode: verity file whose Merkle items we want.
+ * @merkle_index: index of the page in the Merkle tree (as in
+ *                read_merkle_tree_page).
+ *
+ * Returns: page index of the Merkle page.
+ */
+static unsigned long get_verity_mapping_index(struct inode *inode,
+					      pgoff_t merkle_index)
+{
+	/*
+	 * the file is readonly, so i_size can't change here.  We jump
+	 * some pages past the last page to cache our merkles.  The goal
+	 * is just to jump past any hugepages that might be mapped in.
+	 */
+	return (i_size_read(inode) >> PAGE_SHIFT) + 2048 + merkle_index;
+}
+
+/*
+ * fsverity op that reads and caches a merkle tree page.  These are stored
+ * in the btree, but we cache them in the inode's address space after EOF.
+ */
+static struct page *btrfs_read_merkle_tree_page(struct inode *inode,
+					       pgoff_t index,
+					       unsigned long num_ra_pages)
+{
+	struct page *p;
+	u64 start = index << PAGE_SHIFT;
+	unsigned long mapping_index = get_verity_mapping_index(inode, index);
+	ssize_t ret;
+	int err;
+
+again:
+	p = find_get_page_flags(inode->i_mapping, mapping_index, FGP_ACCESSED);
+	if (p) {
+		if (PageUptodate(p))
+			return p;
+
+		lock_page(p);
+		/*
+		 * we only insert uptodate pages, so !Uptodate has to be
+		 * an error
+		 */
+		if (!PageUptodate(p)) {
+			unlock_page(p);
+			put_page(p);
+			return ERR_PTR(-EIO);
+		}
+		unlock_page(p);
+		return p;
+	}
+
+	p = page_cache_alloc(inode->i_mapping);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * merkle item keys are indexed from byte 0 in the merkle tree.
+	 * they have the form:
+	 *
+	 * [ inode objectid, BTRFS_MERKLE_ITEM_KEY, offset in bytes ]
+	 */
+	ret = read_key_bytes(BTRFS_I(inode),
+			     BTRFS_VERITY_MERKLE_ITEM_KEY, start,
+			     page_address(p), PAGE_SIZE, p);
+	if (ret < 0) {
+		put_page(p);
+		return ERR_PTR(ret);
+	}
+
+	/* zero fill any bytes we didn't write into the page */
+	if (ret < PAGE_SIZE) {
+		char *kaddr = kmap_atomic(p);
+
+		memset(kaddr + ret, 0, PAGE_SIZE - ret);
+		kunmap_atomic(kaddr);
+	}
+	SetPageUptodate(p);
+	err = add_to_page_cache_lru(p, inode->i_mapping, mapping_index,
+				    mapping_gfp_mask(inode->i_mapping));
+
+	if (!err) {
+		/* inserted and ready for fsverity */
+		unlock_page(p);
+	} else {
+		put_page(p);
+		/* did someone race us into inserting this page? */
+		if (err == -EEXIST)
+			goto again;
+		p = ERR_PTR(err);
+	}
+	return p;
+}
+
+/*
+ * fsverity op that writes a merkle tree block into the btree in 1k chunks.
+ */
+static int btrfs_write_merkle_tree_block(struct inode *inode, const void *buf,
+					u64 index, int log_blocksize)
+{
+	u64 start = index << log_blocksize;
+	u64 len = 1 << log_blocksize;
+	unsigned long mapping_index = get_verity_mapping_index(inode, index);
+
+	if (mapping_index > inode->i_sb->s_maxbytes >> PAGE_SHIFT)
+		return -EFBIG;
+
+	return write_key_bytes(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY,
+			       start, buf, len);
+}
+
+const struct fsverity_operations btrfs_verityops = {
+	.begin_enable_verity	= btrfs_begin_enable_verity,
+	.end_enable_verity	= btrfs_end_enable_verity,
+	.get_verity_descriptor	= btrfs_get_verity_descriptor,
+	.read_merkle_tree_page	= btrfs_read_merkle_tree_page,
+	.write_merkle_tree_block = btrfs_write_merkle_tree_block,
+};
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 5df73001aad4..fa21c8aac78d 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -288,6 +288,7 @@ struct btrfs_ioctl_fs_info_args {
  * first mount when booting older kernel versions.
  */
 #define BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID	(1ULL << 1)
+#define BTRFS_FEATURE_COMPAT_RO_VERITY		(1ULL << 2)
 
 #define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF	(1ULL << 0)
 #define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL	(1ULL << 1)
@@ -308,7 +309,6 @@ struct btrfs_ioctl_fs_info_args {
 #define BTRFS_FEATURE_INCOMPAT_METADATA_UUID	(1ULL << 10)
 #define BTRFS_FEATURE_INCOMPAT_RAID1C34		(1ULL << 11)
 #define BTRFS_FEATURE_INCOMPAT_ZONED		(1ULL << 12)
-
 struct btrfs_ioctl_feature_flags {
 	__u64 compat_flags;
 	__u64 compat_ro_flags;
diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index ae25280316bd..2be57416f886 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -118,6 +118,14 @@
 #define BTRFS_INODE_REF_KEY		12
 #define BTRFS_INODE_EXTREF_KEY		13
 #define BTRFS_XATTR_ITEM_KEY		24
+
+/*
+ * fsverity has a descriptor per file, and then
+ * a number of sha or csum items indexed by offset in to the file.
+ */
+#define BTRFS_VERITY_DESC_ITEM_KEY	36
+#define BTRFS_VERITY_MERKLE_ITEM_KEY	37
+
 #define BTRFS_ORPHAN_ITEM_KEY		48
 /* reserve 2-15 close to the inode for later flexibility */
 
@@ -996,4 +1004,11 @@ struct btrfs_qgroup_limit_item {
 	__le64 rsv_excl;
 } __attribute__ ((__packed__));
 
+struct btrfs_verity_descriptor_item {
+	/* size of the verity descriptor in bytes */
+	__le64 size;
+	__le64 reserved[2];
+	__u8 encryption;
+} __attribute__ ((__packed__));
+
 #endif /* _BTRFS_CTREE_H_ */
-- 
2.24.1

Re: [PATCH v2 2/5] btrfs: initial fsverity support

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 3142 bytes --]

Hi Boris,

I love your patch! Yet something to improve:

[auto build test ERROR on v5.12-rc2]
[also build test ERROR on next-20210305]
[cannot apply to kdave/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Boris-Burkov/btrfs-support-fsverity/20210307-105111
base:    a38fd8748464831584a19438cbb3082b5a2dab15
config: i386-randconfig-m021-20210307 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/230ae9030c4636229de25a9013d979fc8e04f459
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Boris-Burkov/btrfs-support-fsverity/20210307-105111
        git checkout 230ae9030c4636229de25a9013d979fc8e04f459
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   fs/btrfs/super.c: In function 'btrfs_fill_super':
>> fs/btrfs/super.c:1342:6: error: 'struct super_block' has no member named 's_vop'; did you mean 's_op'?
    1342 |  sb->s_vop = &btrfs_verityops;
         |      ^~~~~
         |      s_op


vim +1342 fs/btrfs/super.c

  1328	
  1329	static int btrfs_fill_super(struct super_block *sb,
  1330				    struct btrfs_fs_devices *fs_devices,
  1331				    void *data)
  1332	{
  1333		struct inode *inode;
  1334		struct btrfs_fs_info *fs_info = btrfs_sb(sb);
  1335		int err;
  1336	
  1337		sb->s_maxbytes = MAX_LFS_FILESIZE;
  1338		sb->s_magic = BTRFS_SUPER_MAGIC;
  1339		sb->s_op = &btrfs_super_ops;
  1340		sb->s_d_op = &btrfs_dentry_operations;
  1341		sb->s_export_op = &btrfs_export_ops;
> 1342		sb->s_vop = &btrfs_verityops;
  1343		sb->s_xattr = btrfs_xattr_handlers;
  1344		sb->s_time_gran = 1;
  1345	#ifdef CONFIG_BTRFS_FS_POSIX_ACL
  1346		sb->s_flags |= SB_POSIXACL;
  1347	#endif
  1348		sb->s_flags |= SB_I_VERSION;
  1349		sb->s_iflags |= SB_I_CGROUPWB;
  1350	
  1351		err = super_setup_bdi(sb);
  1352		if (err) {
  1353			btrfs_err(fs_info, "super_setup_bdi failed");
  1354			return err;
  1355		}
  1356	
  1357		err = open_ctree(sb, fs_devices, (char *)data);
  1358		if (err) {
  1359			btrfs_err(fs_info, "open_ctree failed");
  1360			return err;
  1361		}
  1362	
  1363		inode = btrfs_iget(sb, BTRFS_FIRST_FREE_OBJECTID, fs_info->fs_root);
  1364		if (IS_ERR(inode)) {
  1365			err = PTR_ERR(inode);
  1366			goto fail_close;
  1367		}
  1368	
  1369		sb->s_root = d_make_root(inode);
  1370		if (!sb->s_root) {
  1371			err = -ENOMEM;
  1372			goto fail_close;
  1373		}
  1374	
  1375		cleancache_init_fs(sb);
  1376		sb->s_flags |= SB_ACTIVE;
  1377		return 0;
  1378	
  1379	fail_close:
  1380		close_ctree(fs_info);
  1381		return err;
  1382	}
  1383	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 38975 bytes --]

Re: [PATCH v2 2/5] btrfs: initial fsverity support

[Eric Biggers]

On Fri, Mar 05, 2021 at 11:26:30AM -0800, Boris Burkov wrote:
> +static int end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
>  {
> -	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
> +	int ret = 0;
> +	struct inode *inode = page->mapping->host;
> +	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>  
>  	ASSERT(page_offset(page) <= start &&
>  		start + len <= page_offset(page) + PAGE_SIZE);
>  
>  	if (uptodate) {
> -		btrfs_page_set_uptodate(fs_info, page, start, len);
> +		/*
> +		 * buffered reads of a file with page alignment will issue a
> +		 * 0 length read for one page past the end of file, so we must
> +		 * explicitly skip checking verity on that page of zeros.
> +		 */
> +		if (!PageError(page) && !PageUptodate(page) &&
> +		    start < i_size_read(inode) &&
> +		    fsverity_active(inode) &&
> +		    fsverity_verify_page(page) != true)
> +			ret = -EIO;
> +		else
> +			btrfs_page_set_uptodate(fs_info, page, start, len);
>  	} else {

'fsverity_verify_page(page) != true' is better written as
'!fsverity_verify_page(page)'.

> +/*
> + * Just like ext4, we cache the merkle tree in pages after EOF in the page
> + * cache.  Unlike ext4, we're storing these in dedicated btree items and
> + * not just shoving them after EOF in the file.  This means we'll need to
> + * do extra work to encrypt them once encryption is supported in btrfs,
> + * but btrfs has a lot of careful code around i_size and it seems better
> + * to make a new key type than try and adjust all of our expectations
> + * for i_size.
> + *
> + * fs verity items are stored under two different key types on disk.
> + *
> + * The descriptor items:
> + * [ inode objectid, BTRFS_VERITY_DESC_ITEM_KEY, offset ]
> + *
> + * At offset 0, we store a btrfs_verity_descriptor_item which tracks the
> + * size of the descriptor item and some extra data for encryption.

Is the separate size field really needed?  It seems like the type of thing that
would be redundant with information that btrfs already stores about the tree
items.  Having two sources of truth is error-prone.

> +/*
> + * Insert and write inode items with a given key type and offset.
> + * @inode: The inode to insert for.
> + * @key_type: The key type to insert.
> + * @offset: The item offset to insert at.
> + * @src: Source data to write.
> + * @len: Length of source data to write.
> + * @max_item_size: Break up the write into items of this size at most.
> + *                 Useful for small leaf size file systems.
> + *
> + * Write len bytes from src into items of up to max_item_size length.
> + * The inserted items will have key <ino, key_type, offset + off> where
> + * off is consecutively increasing from 0 up to the last item ending at
> + * offset + len.
> + *
> + * Returns 0 on success and a negative error code on failure.
> + */
> +static int write_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
> +			   const char *src, u64 len)

The max_item_size parameter is documented but doesn't exist.

> +/*
> + * fsverity op that gets the struct fsverity_descriptor.
> + * fsverity does a two pass setup for reading the descriptor, in the first pass
> + * it calls with buf_size = 0 to query the size of the descriptor,
> + * and then in the second pass it actually reads the descriptor off
> + * disk.
> + */
> +static int btrfs_get_verity_descriptor(struct inode *inode, void *buf,
> +				       size_t buf_size)
> +{
> +	size_t true_size;
> +	ssize_t ret = 0;
> +	struct btrfs_verity_descriptor_item item;
> +
> +	memset(&item, 0, sizeof(item));
> +	ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY,
> +			     0, (char *)&item, sizeof(item), NULL);
> +	if (ret < 0)
> +		return ret;
> +
> +	true_size = btrfs_stack_verity_descriptor_size(&item);
> +	if (!buf_size)
> +		return true_size;
> +	if (buf_size < true_size)
> +		return -ERANGE;


It would be good to validate that true_size <= INT_MAX, as it's returned it an
'int'.

> +
> +	ret = read_key_bytes(BTRFS_I(inode),
> +			     BTRFS_VERITY_DESC_ITEM_KEY, 1,
> +			     buf, buf_size, NULL);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != buf_size)
> +		return -EIO;
> +
> +	return buf_size;

Shouldn't this part use true_size, not buf_size?

> +/*
> + * fsverity op that writes a merkle tree block into the btree in 1k chunks.
> + */
> +static int btrfs_write_merkle_tree_block(struct inode *inode, const void *buf,
> +					u64 index, int log_blocksize)
> +{
> +	u64 start = index << log_blocksize;
> +	u64 len = 1 << log_blocksize;
> +	unsigned long mapping_index = get_verity_mapping_index(inode, index);
> +
> +	if (mapping_index > inode->i_sb->s_maxbytes >> PAGE_SHIFT)
> +		return -EFBIG;

I don't think this overflow check will work correctly, as 'mapping_index' can
overflow a ULONG_MAX before the overflow check is done.

> +struct btrfs_verity_descriptor_item {
> +	/* size of the verity descriptor in bytes */
> +	__le64 size;
> +	__le64 reserved[2];
> +	__u8 encryption;
> +} __attribute__ ((__packed__));

Should these reserved fields be strictly validated?  Currently they appear to be
ignored.

- Eric

Re: [PATCH v2 2/5] btrfs: initial fsverity support

[Boris Burkov]

On Mon, Mar 15, 2021 at 04:17:17PM -0700, Eric Biggers wrote:
> On Fri, Mar 05, 2021 at 11:26:30AM -0800, Boris Burkov wrote:
> > +static int end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
> >  {
> > -	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
> > +	int ret = 0;
> > +	struct inode *inode = page->mapping->host;
> > +	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> >  
> >  	ASSERT(page_offset(page) <= start &&
> >  		start + len <= page_offset(page) + PAGE_SIZE);
> >  
> >  	if (uptodate) {
> > -		btrfs_page_set_uptodate(fs_info, page, start, len);
> > +		/*
> > +		 * buffered reads of a file with page alignment will issue a
> > +		 * 0 length read for one page past the end of file, so we must
> > +		 * explicitly skip checking verity on that page of zeros.
> > +		 */
> > +		if (!PageError(page) && !PageUptodate(page) &&
> > +		    start < i_size_read(inode) &&
> > +		    fsverity_active(inode) &&
> > +		    fsverity_verify_page(page) != true)
> > +			ret = -EIO;
> > +		else
> > +			btrfs_page_set_uptodate(fs_info, page, start, len);
> >  	} else {
> 
> 'fsverity_verify_page(page) != true' is better written as
> '!fsverity_verify_page(page)'.
> 
> > +/*
> > + * Just like ext4, we cache the merkle tree in pages after EOF in the page
> > + * cache.  Unlike ext4, we're storing these in dedicated btree items and
> > + * not just shoving them after EOF in the file.  This means we'll need to
> > + * do extra work to encrypt them once encryption is supported in btrfs,
> > + * but btrfs has a lot of careful code around i_size and it seems better
> > + * to make a new key type than try and adjust all of our expectations
> > + * for i_size.
> > + *
> > + * fs verity items are stored under two different key types on disk.
> > + *
> > + * The descriptor items:
> > + * [ inode objectid, BTRFS_VERITY_DESC_ITEM_KEY, offset ]
> > + *
> > + * At offset 0, we store a btrfs_verity_descriptor_item which tracks the
> > + * size of the descriptor item and some extra data for encryption.
> 
> Is the separate size field really needed?  It seems like the type of thing that
> would be redundant with information that btrfs already stores about the tree
> items.  Having two sources of truth is error-prone.

For the case where the user supplied signature is absent or fits in one
1K btrfs verity descriptor item, I believe you are right, and we could
infer that from the generic item size. Assuming arbitrary signature
lengths, we could still probably do it by searching for the last item
and computing the size from its key offset and item size. Though now
that we have a special meaning for offset 0, that gets a bit messier.

I believe we will need the special item no matter what for the eventual
encryption case, so I figured it wasn't a big deal to include the size
rather than try to come up with some computation to get it. I like the
argument about redundant representation, and saving 8 bytes per verity
enabled file isn't nothing either. I will see if I can compute it
efficiently without adding the extra field.

> 
> > +/*
> > + * Insert and write inode items with a given key type and offset.
> > + * @inode: The inode to insert for.
> > + * @key_type: The key type to insert.
> > + * @offset: The item offset to insert at.
> > + * @src: Source data to write.
> > + * @len: Length of source data to write.
> > + * @max_item_size: Break up the write into items of this size at most.
> > + *                 Useful for small leaf size file systems.
> > + *
> > + * Write len bytes from src into items of up to max_item_size length.
> > + * The inserted items will have key <ino, key_type, offset + off> where
> > + * off is consecutively increasing from 0 up to the last item ending at
> > + * offset + len.
> > + *
> > + * Returns 0 on success and a negative error code on failure.
> > + */
> > +static int write_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
> > +			   const char *src, u64 len)
> 
> The max_item_size parameter is documented but doesn't exist.
> 
> > +/*
> > + * fsverity op that gets the struct fsverity_descriptor.
> > + * fsverity does a two pass setup for reading the descriptor, in the first pass
> > + * it calls with buf_size = 0 to query the size of the descriptor,
> > + * and then in the second pass it actually reads the descriptor off
> > + * disk.
> > + */
> > +static int btrfs_get_verity_descriptor(struct inode *inode, void *buf,
> > +				       size_t buf_size)
> > +{
> > +	size_t true_size;
> > +	ssize_t ret = 0;
> > +	struct btrfs_verity_descriptor_item item;
> > +
> > +	memset(&item, 0, sizeof(item));
> > +	ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY,
> > +			     0, (char *)&item, sizeof(item), NULL);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	true_size = btrfs_stack_verity_descriptor_size(&item);
> > +	if (!buf_size)
> > +		return true_size;
> > +	if (buf_size < true_size)
> > +		return -ERANGE;
> 
> 
> It would be good to validate that true_size <= INT_MAX, as it's returned it an
> 'int'.
> 
> > +
> > +	ret = read_key_bytes(BTRFS_I(inode),
> > +			     BTRFS_VERITY_DESC_ITEM_KEY, 1,
> > +			     buf, buf_size, NULL);
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != buf_size)
> > +		return -EIO;
> > +
> > +	return buf_size;
> 
> Shouldn't this part use true_size, not buf_size?

I felt this was clunky when writing it. If I'm not mistaken, it doesn't
really matter what we return since the actual key line is the
`ret != buf_size` check above.

I think it would be reasonable to allow too-large buffers and check
against/return true_size. If true_size is somehow wrong, then presumably
the signature check itself will still fail.

> 
> > +/*
> > + * fsverity op that writes a merkle tree block into the btree in 1k chunks.
> > + */
> > +static int btrfs_write_merkle_tree_block(struct inode *inode, const void *buf,
> > +					u64 index, int log_blocksize)
> > +{
> > +	u64 start = index << log_blocksize;
> > +	u64 len = 1 << log_blocksize;
> > +	unsigned long mapping_index = get_verity_mapping_index(inode, index);
> > +
> > +	if (mapping_index > inode->i_sb->s_maxbytes >> PAGE_SHIFT)
> > +		return -EFBIG;
> 
> I don't think this overflow check will work correctly, as 'mapping_index' can
> overflow a ULONG_MAX before the overflow check is done.

Oof, I had a bit of trouble with this, so it's not too surprising I got
it wrong. I misunderstood the maxbytes logic for systems with 32 bit
longs, and obviously only tested it my machine with 64 bit longs.
> 
> > +struct btrfs_verity_descriptor_item {
> > +	/* size of the verity descriptor in bytes */
> > +	__le64 size;
> > +	__le64 reserved[2];
> > +	__u8 encryption;
> > +} __attribute__ ((__packed__));
> 
> Should these reserved fields be strictly validated?  Currently they appear to be
> ignored.
> 
> - Eric

Thanks for the review,
Boris

Re: [PATCH v2 2/5] btrfs: initial fsverity support

[Eric Biggers]

On Mon, Mar 15, 2021 at 05:42:48PM -0700, Boris Burkov wrote:
> > Is the separate size field really needed?  It seems like the type of thing that
> > would be redundant with information that btrfs already stores about the tree
> > items.  Having two sources of truth is error-prone.
> 
> For the case where the user supplied signature is absent or fits in one
> 1K btrfs verity descriptor item, I believe you are right, and we could
> infer that from the generic item size. Assuming arbitrary signature
> lengths, we could still probably do it by searching for the last item
> and computing the size from its key offset and item size. Though now
> that we have a special meaning for offset 0, that gets a bit messier.
> 
> I believe we will need the special item no matter what for the eventual
> encryption case, so I figured it wasn't a big deal to include the size
> rather than try to come up with some computation to get it. I like the
> argument about redundant representation, and saving 8 bytes per verity
> enabled file isn't nothing either. I will see if I can compute it
> efficiently without adding the extra field.

To be clear, I'm not necessarily saying "remove the size field".  But if you
keep it, it needs a proper explanation and careful consideration of what to do
if it doesn't match the actual size.

I don't think 8 bytes per file matters, especially when the Merkle tree blocks
are zero-padded to 4096 bytes anyway.

> > > +	true_size = btrfs_stack_verity_descriptor_size(&item);
> > > +	if (!buf_size)
> > > +		return true_size;
> > > +	if (buf_size < true_size)
> > > +		return -ERANGE;
> > 
> > 
> > It would be good to validate that true_size <= INT_MAX, as it's returned it an
> > 'int'.
> > 
> > > +
> > > +	ret = read_key_bytes(BTRFS_I(inode),
> > > +			     BTRFS_VERITY_DESC_ITEM_KEY, 1,
> > > +			     buf, buf_size, NULL);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +	if (ret != buf_size)
> > > +		return -EIO;
> > > +
> > > +	return buf_size;
> > 
> > Shouldn't this part use true_size, not buf_size?
> 
> I felt this was clunky when writing it. If I'm not mistaken, it doesn't
> really matter what we return since the actual key line is the
> `ret != buf_size` check above.
> 
> I think it would be reasonable to allow too-large buffers and check
> against/return true_size. If true_size is somehow wrong, then presumably
> the signature check itself will still fail.

fsverity_operations::get_verity_descriptor() is supposed to behave like
getxattr().  That means that if the buffer provided is too large, the function
shouldn't fail but rather just read and return the actual size.

That means using true_size above.

I probably should have gone with something harder to get wrong, but getxattr()
semantics seemed "simple".

- Eric

Re: [PATCH v2 2/5] btrfs: initial fsverity support

[Eric Biggers]

On Fri, Mar 05, 2021 at 11:26:30AM -0800, Boris Burkov wrote:
> +/*
> + * fsverity op that ends enabling verity.
> + * fsverity calls this when it's done with all of the pages in the file
> + * and all of the merkle items have been inserted.  We write the
> + * descriptor and update the inode in the btree to reflect its new life
> + * as a verity file.
> + */
> +static int btrfs_end_enable_verity(struct file *filp, const void *desc,
> +				  size_t desc_size, u64 merkle_tree_size)
> +{
> +	struct btrfs_trans_handle *trans;
> +	struct inode *inode = file_inode(filp);
> +	struct btrfs_root *root = BTRFS_I(inode)->root;
> +	struct btrfs_verity_descriptor_item item;
> +	int ret;
> +
> +	if (desc != NULL) {
> +		/* write out the descriptor item */
> +		memset(&item, 0, sizeof(item));
> +		btrfs_set_stack_verity_descriptor_size(&item, desc_size);
> +		ret = write_key_bytes(BTRFS_I(inode),
> +				      BTRFS_VERITY_DESC_ITEM_KEY, 0,
> +				      (const char *)&item, sizeof(item));
> +		if (ret)
> +			goto out;
> +		/* write out the descriptor itself */
> +		ret = write_key_bytes(BTRFS_I(inode),
> +				      BTRFS_VERITY_DESC_ITEM_KEY, 1,
> +				      desc, desc_size);
> +		if (ret)
> +			goto out;
> +
> +		/* update our inode flags to include fs verity */
> +		trans = btrfs_start_transaction(root, 1);
> +		if (IS_ERR(trans)) {
> +			ret = PTR_ERR(trans);
> +			goto out;
> +		}
> +		BTRFS_I(inode)->compat_flags |= BTRFS_INODE_VERITY;
> +		btrfs_sync_inode_flags_to_i_flags(inode);
> +		ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
> +		btrfs_end_transaction(trans);
> +	}
> +
> +out:
> +	if (desc == NULL || ret) {
> +		/* If we failed, drop all the verity items */
> +		drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY);
> +		drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY);
> +	} else
> +		btrfs_set_fs_compat_ro(root->fs_info, VERITY);
> +	clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags);
> +	return ret;
> +}

If enabling verity failed, I think you also need to call
truncate_inode_pages(inode->i_mapping, inode->i_size)
to remove the cached Merkle tree pages from the page cache.  Otherwise they can
be exposed to userspace if the file is later extended.  I recently fixed this
same problem for ext4 and f2fs:
https://lkml.kernel.org/linux-f2fs-devel/20210302200420.137977-1-ebiggers@kernel.org/T/#u

- Eric

[PATCH v2 3/5] btrfs: check verity for reads of inline extents and holes

[Boris Burkov]

The majority of reads receive a verity check after the bio is complete
as the page is marked uptodate. However, there is a class of reads which
are handled with btrfs logic in readpage, rather than by submitting a
bio. Specifically, these are inline extents, preallocated extents, and
holes. Tweak readpage so that if it is going to mark such a page
uptodate, it first checks verity on it.

Now if a veritied file has corruption to this class of EXTENT_DATA
items, it will be detected at read time.

There is one annoying edge case that requires checking for start <
last_byte: if userspace reads to the end of a file with page aligned
size and then tries to keep reading (as cat does), the buffered read
code will try to read the page past the end of the file, and expects it
to be filled with 0s and marked uptodate. That bogus page is not part of
the data hashed by verity, so we have to ignore it.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/extent_io.c | 26 +++++++-------------------
 1 file changed, 7 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 0d6f8b33830f..653b066f3043 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2201,18 +2201,6 @@ int test_range_bit(struct extent_io_tree *tree, u64 start, u64 end,
 	return bitset;
 }
 
-/*
- * helper function to set a given page up to date if all the
- * extents in the tree for that page are up to date
- */
-static void check_page_uptodate(struct extent_io_tree *tree, struct page *page)
-{
-	u64 start = page_offset(page);
-	u64 end = start + PAGE_SIZE - 1;
-	if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1, NULL))
-		SetPageUptodate(page);
-}
-
 int free_io_failure(struct extent_io_tree *failure_tree,
 		    struct extent_io_tree *io_tree,
 		    struct io_failure_record *rec)
@@ -3427,14 +3415,14 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 					    &cached, GFP_NOFS);
 			unlock_extent_cached(tree, cur,
 					     cur + iosize - 1, &cached);
-			end_page_read(page, true, cur, iosize);
+			ret = end_page_read(page, true, cur, iosize);
 			break;
 		}
 		em = __get_extent_map(inode, page, pg_offset, cur,
 				      end - cur + 1, em_cached);
 		if (IS_ERR_OR_NULL(em)) {
 			unlock_extent(tree, cur, end);
-			end_page_read(page, false, cur, end + 1 - cur);
+			ret = end_page_read(page, false, cur, end + 1 - cur);
 			break;
 		}
 		extent_offset = cur - em->start;
@@ -3515,9 +3503,10 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 
 			set_extent_uptodate(tree, cur, cur + iosize - 1,
 					    &cached, GFP_NOFS);
+
 			unlock_extent_cached(tree, cur,
 					     cur + iosize - 1, &cached);
-			end_page_read(page, true, cur, iosize);
+			ret = end_page_read(page, true, cur, iosize);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;
@@ -3525,9 +3514,8 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		/* the get_extent function already copied into the page */
 		if (test_range_bit(tree, cur, cur_end,
 				   EXTENT_UPTODATE, 1, NULL)) {
-			check_page_uptodate(tree, page);
 			unlock_extent(tree, cur, cur + iosize - 1);
-			end_page_read(page, true, cur, iosize);
+			ret = end_page_read(page, true, cur, iosize);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;
@@ -3537,7 +3525,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		 */
 		if (block_start == EXTENT_MAP_INLINE) {
 			unlock_extent(tree, cur, cur + iosize - 1);
-			end_page_read(page, false, cur, iosize);
+			ret = end_page_read(page, false, cur, iosize);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;
@@ -3555,7 +3543,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 			*bio_flags = this_bio_flag;
 		} else {
 			unlock_extent(tree, cur, cur + iosize - 1);
-			end_page_read(page, false, cur, iosize);
+			ret = end_page_read(page, false, cur, iosize);
 			goto out;
 		}
 		cur = cur + iosize;
-- 
2.24.1

[PATCH v2 4/5] btrfs: fallback to buffered io for verity files

[Boris Burkov]

Reading the contents with direct IO would circumvent verity checks, so
fallback to buffered reads. For what it's worth, this is how ext4
handles it as well.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 75f1406021e5..c948c30e132c 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3623,6 +3623,9 @@ static ssize_t btrfs_direct_read(struct kiocb *iocb, struct iov_iter *to)
 	struct inode *inode = file_inode(iocb->ki_filp);
 	ssize_t ret;
 
+	if (fsverity_active(inode))
+		return 0;
+
 	if (check_direct_read(btrfs_sb(inode->i_sb), to, iocb->ki_pos))
 		return 0;
 
-- 
2.24.1

[PATCH v2 5/5] btrfs: verity metadata orphan items

[Boris Burkov]

If we don't finish creating fsverity metadata for a file, or fail to
clean up already created metadata after a failure, we could leak the
verity items.

To address this issue, we use the orphan mechanism. When we start
enabling verity on a file, we also add an orphan item for that inode.
When we are finished, we delete the orphan. However, if we are
interrupted midway, the orphan will be present at mount and we can
cleanup the half-formed verity state.

One thing to note is that this is a resurrection of using orphans to
signal orphaned metadata that isn't the inode itself. This makes the
comment discussing deprecating that concept a bit messy in full context.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/inode.c  | 15 +++++++--
 fs/btrfs/verity.c | 80 +++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 83 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 9291f6633bc6..7c00863ba8a3 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3419,7 +3419,9 @@ int btrfs_orphan_cleanup(struct btrfs_root *root)
 
 		/*
 		 * If we have an inode with links, there are a couple of
-		 * possibilities. Old kernels (before v3.12) used to create an
+		 * possibilities:
+		 *
+		 * 1. Old kernels (before v3.12) used to create an
 		 * orphan item for truncate indicating that there were possibly
 		 * extent items past i_size that needed to be deleted. In v3.12,
 		 * truncate was changed to update i_size in sync with the extent
@@ -3432,13 +3434,22 @@ int btrfs_orphan_cleanup(struct btrfs_root *root)
 		 * slim, and it's a pain to do the truncate now, so just delete
 		 * the orphan item.
 		 *
+		 * 2. We were halfway through creating fsverity metadata for the
+		 * file. In that case, the orphan item represents incomplete
+		 * fsverity metadata which must be cleaned up with
+		 * btrfs_drop_verity_items.
+		 *
 		 * It's also possible that this orphan item was supposed to be
 		 * deleted but wasn't. The inode number may have been reused,
 		 * but either way, we can delete the orphan item.
 		 */
 		if (ret == -ENOENT || inode->i_nlink) {
-			if (!ret)
+			if (!ret) {
+				ret = btrfs_drop_verity_items(BTRFS_I(inode));
 				iput(inode);
+				if (ret)
+					goto out;
+			}
 			trans = btrfs_start_transaction(root, 1);
 			if (IS_ERR(trans)) {
 				ret = PTR_ERR(trans);
diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
index 648bda5a3716..b677288db411 100644
--- a/fs/btrfs/verity.c
+++ b/fs/btrfs/verity.c
@@ -350,6 +350,60 @@ static ssize_t read_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset
 	return ret;
 }
 
+static int add_orphan(struct btrfs_inode *inode)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *root = inode->root;
+	int ret = 0;
+
+	trans = btrfs_start_transaction(root, 1);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto out;
+	}
+	ret = btrfs_orphan_add(trans, inode);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+	btrfs_end_transaction(trans);
+
+out:
+	return ret;
+}
+
+static int del_orphan(struct btrfs_inode *inode)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *root = inode->root;
+	int ret;
+
+	trans = btrfs_start_transaction(root, 1);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	ret = btrfs_del_orphan_item(trans, root, btrfs_ino(inode));
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+	btrfs_end_transaction(trans);
+
+out:
+	return ret;
+}
+
+int btrfs_drop_verity_items(struct btrfs_inode *inode)
+{
+	int ret;
+
+	ret = drop_verity_items(inode, BTRFS_VERITY_DESC_ITEM_KEY);
+	if (ret)
+		return ret;
+
+	return drop_verity_items(inode, BTRFS_VERITY_MERKLE_ITEM_KEY);
+}
+
 /*
  * fsverity op that begins enabling verity.
  * fsverity calls this to ask us to setup the inode for enabling.  We
@@ -363,17 +417,13 @@ static int btrfs_begin_enable_verity(struct file *filp)
 	if (test_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags))
 		return -EBUSY;
 
-	/*
-	 * ext4 adds the inode to the orphan list here, presumably because the
-	 * truncate done at orphan processing time will delete partial
-	 * measurements.  TODO: setup orphans
-	 */
 	set_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags);
-	ret = drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY);
+
+	ret = btrfs_drop_verity_items(BTRFS_I(inode));
 	if (ret)
 		goto err;
 
-	ret = drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY);
+	ret = add_orphan(BTRFS_I(inode));
 	if (ret)
 		goto err;
 
@@ -400,6 +450,7 @@ static int btrfs_end_enable_verity(struct file *filp, const void *desc,
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_verity_descriptor_item item;
 	int ret;
+	int keep_orphan = 0;
 
 	if (desc != NULL) {
 		/* write out the descriptor item */
@@ -431,11 +482,20 @@ static int btrfs_end_enable_verity(struct file *filp, const void *desc,
 
 out:
 	if (desc == NULL || ret) {
-		/* If we failed, drop all the verity items */
-		drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY);
-		drop_verity_items(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY);
+		/*
+		 * If verity failed (here or in the generic code), drop all the
+		 * verity items.
+		 */
+		keep_orphan = btrfs_drop_verity_items(BTRFS_I(inode));
 	} else
 		btrfs_set_fs_compat_ro(root->fs_info, VERITY);
+	/*
+	 * If we are handling an error, but failed to drop the verity items,
+	 * we still need the orphan.
+	 */
+	if (!keep_orphan)
+		del_orphan(BTRFS_I(inode));
+
 	clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &BTRFS_I(inode)->runtime_flags);
 	return ret;
 }
-- 
2.24.1

Re: [PATCH v2 0/5] btrfs: support fsverity

[Eric Biggers]

On Fri, Mar 05, 2021 at 11:26:28AM -0800, Boris Burkov wrote:
> This patchset provides support for fsverity in btrfs.
> 
> At a high level, we store the verity descriptor and Merkle tree data
> in the file system btree with the file's inode as the objectid, and
> direct reads/writes to those items to implement the generic fsverity
> interface required by fs/verity/.
> 
> The first patch is a preparatory patch which adds a notion of
> compat_flags to the btrfs_inode and inode_item in order to allow
> enabling verity on a file without making the file system unmountable for
> older kernels. (It runs afoul of the leaf corruption check otherwise)
> 
> The second patch is the bulk of the fsverity implementation. It
> implements the fsverity interface and adds verity checks for the typical
> file reading case.
> 
> The third patch cleans up the corner cases in readpage, covering inline
> extents, preallocated extents, and holes.
> 
> The fourth patch handles direct io of a veritied file by falling back to
> buffered io.
> 
> The fifth patch handles crashes mid-verity enable via orphan items
> 

Can you include information about how this was tested?

Also, fsverity-utils works with btrfs as-is, correct?

- Eric

Re: [PATCH v2 0/5] btrfs: support fsverity

[Boris Burkov]

On Mon, Mar 15, 2021 at 04:09:41PM -0700, Eric Biggers wrote:
> On Fri, Mar 05, 2021 at 11:26:28AM -0800, Boris Burkov wrote:
> > This patchset provides support for fsverity in btrfs.
> > 
> > At a high level, we store the verity descriptor and Merkle tree data
> > in the file system btree with the file's inode as the objectid, and
> > direct reads/writes to those items to implement the generic fsverity
> > interface required by fs/verity/.
> > 
> > The first patch is a preparatory patch which adds a notion of
> > compat_flags to the btrfs_inode and inode_item in order to allow
> > enabling verity on a file without making the file system unmountable for
> > older kernels. (It runs afoul of the leaf corruption check otherwise)
> > 
> > The second patch is the bulk of the fsverity implementation. It
> > implements the fsverity interface and adds verity checks for the typical
> > file reading case.
> > 
> > The third patch cleans up the corner cases in readpage, covering inline
> > extents, preallocated extents, and holes.
> > 
> > The fourth patch handles direct io of a veritied file by falling back to
> > buffered io.
> > 
> > The fifth patch handles crashes mid-verity enable via orphan items
> > 
> 
> Can you include information about how this was tested?

Right now, I'm testing it with the btrfs xfstest I added as well as a
one-off script that corrupts regular extent data. I'm still working on
integrating the btrfs specifics with the generic verity xfstests, and
how to test verity+compression without hacks.

> 
> Also, fsverity-utils works with btrfs as-is, correct?
> 

As far as I know, yes. I've tested using both the rpm packaged by Fedora
and building from source.

> - Eric