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 AA7F0221FCF; Tue, 17 Feb 2026 23:20:42 +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=1771370442; cv=none; b=PSThI8JzMWwL+MTlVq34uNW6kul58kSQtAkNIw0rKxHOEFsjiuMcPL3fCIg+YpHntGf+KcW/PvUy39+E6j/Y+CmLBpsNQGH+Ko/NbhvSW7+RkEnzubPI+Q2y5x30pXt/vVtAHN27BL6oDDyLkg/okbuKxV9YXn3OaFmRibiQnfM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771370442; c=relaxed/simple; bh=DJSVKyGg+4R0k6WRAuNIeBNAD9pdSqrckhsLvnGW8L4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=c1cTPICWbPxOxo1sjWKthJees+z5cnd/UWvq5TQXs+4GADfq9FcVjbA17guQqCJ+OUFtUKInf3kC79vmSBJfFd14LjPzZmKCRTGSRNyXPtxe7d5XMnUi31Fr/TiwkOxwql7e+yhK5YnxRzgMGZIAXhNfeVtdoEGM0GgrVHqzrQI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YO8XdAbX; 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="YO8XdAbX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 965F6C4CEF7; Tue, 17 Feb 2026 23:20:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771370442; bh=DJSVKyGg+4R0k6WRAuNIeBNAD9pdSqrckhsLvnGW8L4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YO8XdAbXIQ/VvNBhRMjnOq1Dzi+SIVMY3LLNZ8cc8WQ0ax83BQ7RGgzn7M8J4lrko NfTqeESoo5xUxjwRIEXigPwfoOXMZQimUU75K5zXfi4yosWKdjfAQi/OaNmd2Tm2Qp cGLgGDcEgNuakG23vAk5P8IGvHYjdppD5sWGloXy4SAeer9R3uQJ+8rQ0oIwVJgNCd 20y8SLospQPb+dj2wGjtwqXGPJKtO17bLF1o3Qn6o6FkciVZ1I2RJNi3MLXAbTBSJM Tr2+YcWIsSXWEpazLWpCbzAszC+1id7e+VL3qrZx93Ev8WhY2HkCJYb24awEyRO2xY 3eOk17Hl0tmFQ== 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, djwong@kernel.org Subject: [PATCH v3 04/35] fsverity: generate and store zero-block hash Date: Wed, 18 Feb 2026 00:19:04 +0100 Message-ID: <20260217231937.1183679-5-aalbersh@kernel.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260217231937.1183679-1-aalbersh@kernel.org> References: <20260217231937.1183679-1-aalbersh@kernel.org> Precedence: bulk X-Mailing-List: linux-xfs@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. Signed-off-by: Darrick J. Wong Signed-off-by: Andrey Albershteyn --- fs/verity/fsverity_private.h | 3 +++ fs/verity/open.c | 3 +++ 2 files changed, 6 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; -- 2.51.2