[PATCH v2 03/11] fsverity: store log2(digest_size) precomputed

Eric Biggers
2022-12-23T20:37:29Z

From: Eric Biggers <ebiggers@google.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@google.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