linux-kernel - Re: [PATCH v4 15/17] module: Introduce hash-based integrity checking

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Message-ID: <20260113145635.YfSTBhVs@linutronix.de>
Date: Tue, 13 Jan 2026 15:56:35 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Nathan Chancellor <nathan@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Daniel Gomez <da.gomez@...sung.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Jonathan Corbet <corbet@....net>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Naveen N Rao <naveen@...nel.org>, Mimi Zohar <zohar@...ux.ibm.com>,
	Roberto Sassu <roberto.sassu@...wei.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
	Eric Snowberg <eric.snowberg@...cle.com>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Daniel Gomez <da.gomez@...nel.org>,
	Aaron Tomlin <atomlin@...mlin.com>,
	"Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
	Nicolas Schier <nsc@...nel.org>,
	Nicolas Bouchinet <nicolas.bouchinet@....cyber.gouv.fr>,
	Xiu Jianfeng <xiujianfeng@...wei.com>,
	Fabian Grünbichler <f.gruenbichler@...xmox.com>,
	Arnout Engelen <arnout@...t.net>,
	Mattia Rizzolo <mattia@...reri.org>, kpcyrd <kpcyrd@...hlinux.org>,
	Christian Heusel <christian@...sel.eu>,
	Câju Mihai-Drosi <mcaju95@...il.com>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-modules@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-doc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-integrity@...r.kernel.org
Subject: Re: [PATCH v4 15/17] module: Introduce hash-based integrity checking

On 2026-01-13 13:28:59 [+0100], Thomas Weißschuh wrote:
> --- /dev/null
> +++ b/scripts/modules-merkle-tree.c
> @@ -0,0 +1,467 @@
…
> +static void build_proof(struct mtree *mt, unsigned int n, int fd)
> +{
> +	unsigned char cur[EVP_MAX_MD_SIZE];
> +	unsigned char tmp[EVP_MAX_MD_SIZE];

This and a few other instances below could be optimized to avoid
hashing. I probably forgot to let you know.
-> https://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/mtree-hashed-mods.git/commit/?id=10b565c123c731da37befe862de13678b7c54877

> +	struct file_entry *fe, *fe_sib;
> +
> +	fe = &fh_list[n];
> +
> +	if ((n & 1) == 0) {
> +		/* No pair, hash with itself */
> +		if (n + 1 == num_files)
> +			fe_sib = fe;
> +		else
> +			fe_sib = &fh_list[n + 1];
> +	} else {
> +		fe_sib = &fh_list[n - 1];
> +	}
> +	/* First comes the node position into the file */
> +	write_be_int(fd, n);
> +
> +	if ((n & 1) == 0)
> +		hash_entry(fe->hash, fe_sib->hash, cur);
> +	else
> +		hash_entry(fe_sib->hash, fe->hash, cur);
> +
> +	/* Next is the sibling hash, followed by hashes in the tree */
> +	write_hash(fd, fe_sib->hash);
> +
> +	for (unsigned int i = 0; i < mt->levels - 1; i++) {
> +		n >>= 1;
> +		if ((n & 1) == 0) {
> +			void *h;
> +
> +			/* No pair, hash with itself */
> +			if (n + 1 == mt->entries[i])
> +				h = cur;
> +			else
> +				h = mt->l[i][n + 1].hash;
> +
> +			hash_entry(cur, h, tmp);
> +			write_hash(fd, h);
> +		} else {
> +			hash_entry(mt->l[i][n - 1].hash, cur, tmp);
> +			write_hash(fd, mt->l[i][n - 1].hash);
> +		}
> +		memcpy(cur, tmp, hash_size);
> +	}
> +
> +	 /* After all that, the end hash should match the root hash */
> +	if (memcmp(cur, mt->l[mt->levels - 1][0].hash, hash_size))
> +		errx(1, "hash mismatch");
> +}

Sebastian