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

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Date:   Tue, 15 Nov 2022 12:40:57 -0600
From:   Allen Webb <allenwebb@...gle.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
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.

When i get the modinfo for usbhid, there are no aliases listed:
```
localhost ~ # modinfo usbhid
name:           usbhid
filename:       (builtin)
author:         Andreas Gal
author:         Vojtech Pavlik
author:         Jiri Kosina
description:    USB HID core driver
file:           drivers/hid/usbhid/usbhid
license:        GPL
parm:           quirks:Add/modify USB HID quirks by specifying
quirks=vendorID:productID:quirks where vendorID, productID, and quirks
are all in 0x-prefixed hex (array of charp)
parm:           ignoreled:Autosuspend with active leds (uint)
parm:           kbpoll:Polling interval of keyboards (uint)
parm:           jspoll:Polling interval of joysticks (uint)
parm:           mousepoll:Polling interval of mice (uint)
```

bluetooth however has an alias listed:
```
localhost ~ # modinfo bluetooth
filename:
/lib/modules/5.10.154-20424-gea7532c123d8/kernel/net/bluetooth/bluetooth.ko.gz
author:         Marcel Holtmann <marcel@...tmann.org>
description:    Bluetooth Core ver 2.22
version:        2.22
license:        GPL
alias:          net-pf-31
vermagic:       5.10.154-20424-gea7532c123d8 SMP preempt mod_unload
name:           bluetooth
intree:         Y
retpoline:      Y
depends:        ecdh_generic
srcversion:     F8E46CD048C50B0AA1CD471
parm:           disable_esco:Disable eSCO connection creation (bool)
parm:           enable_ecred:Enable enhanced credit flow control mode (bool)
parm:           disable_ertm:Disable enhanced retransmission mode (bool)
```

I believe the reason for this is many modules use `#define
MODULE_DEVICE_TABLE(type, name)` which is a noop for buildin modules.
I have a local patch that resolves that issue here:
See: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3840672/1/include/linux/module.h#b246

However, I probably ought to rework that patch to create the
MODULE_ALIAS defines instead of the buildin.alias file.

On Tue, Nov 15, 2022 at 11:35 AM Luis Chamberlain <mcgrof@...nel.org> wrote:
>
> 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