linux-ext4 - [PATCH v2 03/11] fsverity: store log2(digest

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Message-Id: <20221223203638.41293-4-ebiggers@kernel.org>
Date:   Fri, 23 Dec 2022 12:36:30 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     linux-fscrypt@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-btrfs@...r.kernel.org, linux-xfs@...r.kernel.org,
        Andrey Albershteyn <aalbersh@...hat.com>
Subject: [PATCH v2 03/11] fsverity: store log2(digest_size) precomputed

From: Eric Biggers <ebiggers@...gle.com>

Add log_digestsize to struct merkle_tree_params so that it can be used
in verify.c.  Also save memory by using u8 for all the log_* fields.

Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 fs/verity/fsverity_private.h | 5 +++--
 fs/verity/open.c             | 3 ++-
 fs/verity/verify.c           | 2 +-
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index 48b97f5d05569..fc1c2797fab19 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -42,8 +42,9 @@ struct merkle_tree_params {
 	unsigned int digest_size;	/* same as hash_alg->digest_size */
 	unsigned int block_size;	/* size of data and tree blocks */
 	unsigned int hashes_per_block;	/* number of hashes per tree block */
-	unsigned int log_blocksize;	/* log2(block_size) */
-	unsigned int log_arity;		/* log2(hashes_per_block) */
+	u8 log_digestsize;		/* log2(digest_size) */
+	u8 log_blocksize;		/* log2(block_size) */
+	u8 log_arity;			/* log2(hashes_per_block) */
 	unsigned int num_levels;	/* number of levels in Merkle tree */
 	u64 tree_size;			/* Merkle tree size in bytes */
 	unsigned long tree_pages;	/* Merkle tree size in pages */
diff --git a/fs/verity/open.c b/fs/verity/open.c
index e356eefb54d7b..ca8de73e5a0b8 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -76,7 +76,8 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
 		err = -EINVAL;
 		goto out_err;
 	}
-	params->log_arity = params->log_blocksize - ilog2(params->digest_size);
+	params->log_digestsize = ilog2(params->digest_size);
+	params->log_arity = log_blocksize - params->log_digestsize;
 	params->hashes_per_block = 1 << params->log_arity;
 
 	/*
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index 4c57a1bd01afc..d2fcb6a21ea8e 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -35,7 +35,7 @@ static void hash_at_level(const struct merkle_tree_params *params,
 
 	/* Offset of the wanted hash (in bytes) within the hash block */
 	*hoffset = (position & ((1 << params->log_arity) - 1)) <<
-		   (params->log_blocksize - params->log_arity);
+		   params->log_digestsize;
 }
 
 static inline int cmp_hashes(const struct fsverity_info *vi,
-- 
2.39.0