linux-kernel - Re: [PATCH v2 6/6] module: Introduce hash-based integrity checking

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Message-ID: <169f0e30-a8b2-494d-917e-eade8340cf67@t-8ch.de>
Date: Thu, 6 Mar 2025 09:10:34 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: kpcyrd <kpcyrd@...hlinux.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	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>, Fabian Grünbichler <f.gruenbichler@...xmox.com>, 
	Arnout Engelen <arnout@...t.net>, Mattia Rizzolo <mattia@...reri.org>, 
	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
Subject: Re: [PATCH v2 6/6] module: Introduce hash-based integrity checking

On 2025-01-23 00:28:40+0100, kpcyrd wrote:
> Thanks for reaching out, also your work on this is much appreciated and
> followed with great interest. <3
> 
> On 1/20/25 6:44 PM, Thomas Weißschuh wrote:
> > diff --git a/kernel/module/main.c b/kernel/module/main.c
> > index effe1db02973d4f60ff6cbc0d3b5241a3576fa3e..094ace81d795711b56d12a2abc75ea35449c8300 100644
> > --- a/kernel/module/main.c
> > +++ b/kernel/module/main.c
> > @@ -3218,6 +3218,12 @@ static int module_integrity_check(struct load_info *info, int flags)
> >   {
> >   	int err = 0;
> > +	if (IS_ENABLED(CONFIG_MODULE_HASHES)) {
> > +		err = module_hash_check(info, flags);
> > +		if (!err)
> > +			return 0;
> > +	}
> > +
> >   	if (IS_ENABLED(CONFIG_MODULE_SIG))
> >   		err = module_sig_check(info, flags);
> 
> From how I'm reading this (please let me know if I'm wrong):

<snip>

This is how it is intended, thanks for checking.

> This all seems reasonable to me, maybe the check for
> is_module_sig_enforced() could be moved from kernel/module/signing.c to
> kernel/module/main.c, otherwise `sig_enforce=1` would not have any effect
> for a `CONFIG_MODULE_HASHES && !CONFIG_MODULE_SIG` kernel.

Moving the check would complicate the logic and shouldn't make a
difference. In signing.c it ensures that a validation failure is
propagated. However that is the default behaviour in hashes.c.


Thomas