fsverity: support verification with tree block size < PAGE_SIZE

Add support for verifying data from verity files whose Merkle tree block
size is less than the page size.  The main use case for this is to allow
a single Merkle tree block size to be used across all systems, so that
only one set of fsverity file digests and signatures is needed.

To do this, eliminate various assumptions that the Merkle tree block
size and the page size are the same:

- Make fsverity_verify_page() a wrapper around a new function
  fsverity_verify_blocks() which verifies one or more blocks in a page.

- When a Merkle tree block is needed, get the corresponding page and
  only verify and use the needed portion.  (The Merkle tree continues to
  be read and cached in page-sized chunks; that doesn't need to change.)

- When the Merkle tree block size and page size differ, use a bitmap
  fsverity_info::hash_block_verified to keep track of which Merkle tree
  blocks have been verified, as PageChecked cannot be used directly.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Andrey Albershteyn <aalbersh@redhat.com>
Tested-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20221223203638.41293-7-ebiggers@kernel.org

1 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index f5ed7ecfd9ab..6ecc51f80221 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -170,7 +170,8 @@ int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg);
 
 /* verify.c */
 
-bool fsverity_verify_page(struct page *page);
+bool fsverity_verify_blocks(struct page *page, unsigned int len,
+			    unsigned int offset);
 void fsverity_verify_bio(struct bio *bio);
 void fsverity_enqueue_verify_work(struct work_struct *work);
 
@@ -230,7 +231,8 @@ static inline int fsverity_ioctl_read_metadata(struct file *filp,
 
 /* verify.c */
 
-static inline bool fsverity_verify_page(struct page *page)
+static inline bool fsverity_verify_blocks(struct page *page, unsigned int len,
+					  unsigned int offset)
 {
 	WARN_ON(1);
 	return false;
@@ -248,6 +250,11 @@ static inline void fsverity_enqueue_verify_work(struct work_struct *work)
 
 #endif	/* !CONFIG_FS_VERITY */
 
+static inline bool fsverity_verify_page(struct page *page)
+{
+	return fsverity_verify_blocks(page, PAGE_SIZE, 0);
+}
+
 /**
  * fsverity_active() - do reads from the inode need to go through fs-verity?
  * @inode: inode to check