linux-kernel - Re: [PATCH] modules: add modalias file to sysfs for modules.

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Date:   Tue, 15 Nov 2022 09:35:12 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Allen Webb <allenwebb@...gle.com>
Cc:     Lucas De Marchi <lucas.demarchi@...el.com>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] modules: add modalias file to sysfs for modules.

On Tue, Nov 15, 2022 at 10:05:35AM -0600, Allen Webb wrote:
> On Mon, Nov 14, 2022 at 11:22 AM Lucas De Marchi
> <lucas.demarchi@...el.com> wrote:
> >
> > On Mon, Nov 14, 2022 at 10:42:50AM -0600, Allen Webb wrote:
> > >On Fri, Nov 11, 2022 at 12:29 PM Luis Chamberlain <mcgrof@...nel.org> wrote:
> > >>
> > >> On Fri, Nov 11, 2022 at 09:28:52AM -0600, Allen Webb wrote:
> > >> > USB devices support the authorized attribute which can be used by
> > >> > user-space to implement trust-based systems for enabling USB devices. It
> > >> > would be helpful when building these systems to be able to know in
> > >> > advance which kernel drivers (or modules) are reachable from a
> > >> > particular USB device.
> > >> >
> > >> > This information is readily available for external modules in
> > >> > modules.alias. However, builtin kernel modules are not covered. This
> > >> > patch adds a sys-fs attribute to both builtin and loaded modules
> > >> > exposing the matching rules in the modalias format for integration
> > >> > with tools like USBGuard.
> > >> >
> > >> > Signed-off-by: Allen Webb <allenwebb@...gle.com>
> > >>
> > >> Thanks for the patch Allen!
> > >>
> > >> I'd rather have something generic though, and it would seem kmod [0] already
> > >> does this, have you seen the kmod support for builtin.alias.bin
> > >>
> > >> Can't that be used?
> > >
> > >Probably, but I don't see the builtin.alias.bin in my build. Is it experimental?
> >
> > no. That is generated by depmod since v27 using modules.builtin.modinfo
> > generated by the kernel build system. Highly recommend v30 though
> > as there were fixes in v28 and v29 and some changes to speed up its
> > generation/use in v30:  See entries mentioning
> > builtin.alias and bultin.modinfo in
> > https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/tree/NEWS
> >
> > libkmod/modprobe/modinfo also have the corresponding changes to lookup that
> > index when resolving aliases.
> 
> I see the file but it is largely missing the aliases I am interested
> in, so it looks like I might need to modify my patch that creates
> buildin.alias to add the missing alias defines in the header along
> with the other module metadata for builtin modules. Does this sound
> right to you?

Can you clarify what is missing and why? And an RFC is welcomed if it
helps demonstrates what you mean.

  Luis