From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 67D4F3AA1AF; Tue, 31 Mar 2026 21:28:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774992524; cv=none; b=JVbipspS+VtoThp2akX2HdStOR5vuCfMEEeGRztJIvwrdfJZYlDqrbIEa3lj1cryGK+3gAbwmIR7lVgi3MXAMhK5MBw5M0OtWFvReiWqO0v+3koL/aVPWkolJ/sHwHr3y+hxXPqMo7C2pAou15Co7i2UlinbBAxfUFWXIkmO6R0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774992524; c=relaxed/simple; bh=QrRKSjhxHnv8f+YwIcIJjNn7C1rmXBKEk/PRnbjV/zM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ohgKcignVJdnUW6PnuFEPQtrI7sOEaOn2aPwOrtZ0D177S36SW5iPVVWspSogPjql4P4tUJRrHY7BQ8jNBHPPpJwL3vnimcO96mA143IVhj54+2+Gfzcbzavny/ZpNQFR78zQclm6Uor56ejIBvm412D52x/7yPqw4x6nrxHPSM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c9qCzIF1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="c9qCzIF1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A1963C2BC9E; Tue, 31 Mar 2026 21:28:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774992524; bh=QrRKSjhxHnv8f+YwIcIJjNn7C1rmXBKEk/PRnbjV/zM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=c9qCzIF1hA694H6N7tfiudGv/gAw2vV3xHog5MtGQYffrTZ/ld6aqEK5oWcJjvAu2 SwEph0VLLbn9EaEbZhgwonTV9YWyIdR5pZvF2Nxk2H09iDueVKXB3ocIfaSgIs+xP2 BNMrXqkaRezDGAFETGpzOBUj7GWqopTxxM9uEdrdrUD1lSJrnSfcm4dEOkX/5oIjiC s3+VpEEHOIDuMw1QCLh7OEigWsSogHuRBgPMmc/Kkp1nxVxYUi7n44AWzcZkOf+jFX GLlshhkrI3kXBz/E62+0ZoWSxni5C4qXyyuio77Ks1RSDIB8cfMGK8J3HNbbtjdBd7 kcDxs2occSwog== From: Andrey Albershteyn To: linux-xfs@vger.kernel.org, fsverity@lists.linux.dev, linux-fsdevel@vger.kernel.org, ebiggers@kernel.org Cc: Andrey Albershteyn , hch@lst.de, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-btrfs@vger.kernel.org, djwong@kernel.org Subject: [PATCH v6 03/22] fsverity: generate and store zero-block hash Date: Tue, 31 Mar 2026 23:28:04 +0200 Message-ID: <20260331212827.2631020-4-aalbersh@kernel.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260331212827.2631020-1-aalbersh@kernel.org> References: <20260331212827.2631020-1-aalbersh@kernel.org> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Compute the hash of one filesystem block's worth of zeros. A filesystem implementation can decide to elide merkle tree blocks containing only this hash and synthesize the contents at read time. Let's pretend that there's a file containing six data blocks and whose merkle tree looks roughly like this: root +--leaf0 | +--data0 | +--data1 | `--data2 `--leaf1 +--data3 +--data4 `--data5 If data[0-2] are sparse holes, then leaf0 will contain a repeating sequence of @zero_digest. Therefore, leaf0 need not be written to disk because its contents can be synthesized. A subsequent xfs patch will use this to reduce the size of the merkle tree when dealing with sparse gold master disk images and the like. Add a helper to pre-fill folio with hashes of empty blocks. This will be used by iomap to synthesize blocks full of zero hashes on the fly. Signed-off-by: Darrick J. Wong Signed-off-by: Andrey Albershteyn --- fs/verity/fsverity_private.h | 3 +++ fs/verity/open.c | 3 +++ fs/verity/pagecache.c | 22 ++++++++++++++++++++++ include/linux/fsverity.h | 8 ++++++++ 4 files changed, 36 insertions(+) diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index 6e6854c19078..35636c1e2c41 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -53,6 +53,9 @@ struct merkle_tree_params { u64 tree_size; /* Merkle tree size in bytes */ unsigned long tree_pages; /* Merkle tree size in pages */ + /* the hash of a merkle block-sized buffer of zeroes */ + u8 zero_digest[FS_VERITY_MAX_DIGEST_SIZE]; + /* * Starting block index for each tree level, ordered from leaf level (0) * to root level ('num_levels - 1') diff --git a/fs/verity/open.c b/fs/verity/open.c index 0483db672526..94407a37aa08 100644 --- a/fs/verity/open.c +++ b/fs/verity/open.c @@ -153,6 +153,9 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, goto out_err; } + fsverity_hash_block(params, page_address(ZERO_PAGE(0)), + params->zero_digest); + params->tree_size = offset << log_blocksize; params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT; return 0; diff --git a/fs/verity/pagecache.c b/fs/verity/pagecache.c index 1819314ecaa3..c338dfa3eb18 100644 --- a/fs/verity/pagecache.c +++ b/fs/verity/pagecache.c @@ -2,6 +2,7 @@ /* * Copyright 2019 Google LLC */ +#include "fsverity_private.h" #include #include @@ -56,3 +57,24 @@ void generic_readahead_merkle_tree(struct inode *inode, pgoff_t index, folio_put(folio); } EXPORT_SYMBOL_GPL(generic_readahead_merkle_tree); + +/** + * fsverity_fill_zerohash() - fill folio with hashes of zero data block + * @folio: folio to fill + * @poff: offset in the folio to start + * @plen: length of the range to fill with hashes + * @vi: fsverity info + */ +void fsverity_fill_zerohash(struct folio *folio, size_t poff, size_t plen, + struct fsverity_info *vi) +{ + size_t offset = poff; + + WARN_ON_ONCE(!IS_ALIGNED(poff, vi->tree_params.digest_size)); + WARN_ON_ONCE(!IS_ALIGNED(plen, vi->tree_params.digest_size)); + + for (; offset < (poff + plen); offset += vi->tree_params.digest_size) + memcpy_to_folio(folio, offset, vi->tree_params.zero_digest, + vi->tree_params.digest_size); +} +EXPORT_SYMBOL_GPL(fsverity_fill_zerohash); diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h index 2e3a90aff11e..03f703e5bb40 100644 --- a/include/linux/fsverity.h +++ b/include/linux/fsverity.h @@ -201,6 +201,8 @@ bool fsverity_verify_blocks(struct fsverity_info *vi, struct folio *folio, size_t len, size_t offset); void fsverity_verify_bio(struct fsverity_info *vi, struct bio *bio); void fsverity_enqueue_verify_work(struct work_struct *work); +void fsverity_fill_zerohash(struct folio *folio, size_t poff, size_t plen, + struct fsverity_info *vi); #else /* !CONFIG_FS_VERITY */ @@ -281,6 +283,12 @@ static inline void fsverity_enqueue_verify_work(struct work_struct *work) WARN_ON_ONCE(1); } +static inline void fsverity_fill_zerohash(struct folio *folio, size_t poff, + size_t plen, struct fsverity_info *vi) +{ + WARN_ON_ONCE(1); +} + #endif /* !CONFIG_FS_VERITY */ static inline bool fsverity_verify_folio(struct fsverity_info *vi, -- 2.51.2