Re: [PATCH v2 2/6] driver core: Add common support to skip probe for un-authorized devices

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kuppuswamy Sathyanarayanan 
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Andreas Noever <andreas.noever@gmail.com>,
	Michael Jamet <michael.jamet@intel.com>,
	Yehezkel Bernat <YehezkelShB@gmail.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Jason Wang <jasowang@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-usb@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v2 2/6] driver core: Add common support to skip probe for un-authorized devices
Date: Thu, 30 Sep 2021 11:00:07 -0400	[thread overview]
Message-ID: <20210930105852-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <YVXOc3IbcHsVXUxr@kroah.com>

On Thu, Sep 30, 2021 at 04:49:23PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Sep 30, 2021 at 10:38:42AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Sep 30, 2021 at 03:52:52PM +0200, Greg Kroah-Hartman wrote:
> > > On Thu, Sep 30, 2021 at 06:59:36AM -0400, Michael S. Tsirkin wrote:
> > > > On Wed, Sep 29, 2021 at 06:05:07PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > > > > While the common case for device-authorization is to skip probe of
> > > > > unauthorized devices, some buses may still want to emit a message on
> > > > > probe failure (Thunderbolt), or base probe failures on the
> > > > > authorization status of a related device like a parent (USB). So add
> > > > > an option (has_probe_authorization) in struct bus_type for the bus
> > > > > driver to own probe authorization policy.
> > > > > 
> > > > > Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> > > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > > > 
> > > > 
> > > > 
> > > > So what e.g. the PCI patch
> > > > https://lore.kernel.org/all/CACK8Z6E8pjVeC934oFgr=VB3pULx_GyT2NkzAogdRQJ9TKSX9A@mail.gmail.com/
> > > > actually proposes is a list of
> > > > allowed drivers, not devices. Doing it at the device level
> > > > has disadvantages, for example some devices might have a legacy
> > > > unsafe driver, or an out of tree driver. It also does not
> > > > address drivers that poke at hardware during init.
> > > 
> > > Doing it at a device level is the only sane way to do this.
> > > 
> > > A user needs to say "this device is allowed to be controlled by this
> > > driver".  This is the trust model that USB has had for over a decade and
> > > what thunderbolt also has.
> > > 
> > > > Accordingly, I think the right thing to do is to skip
> > > > driver init for disallowed drivers, not skip probe
> > > > for specific devices.
> > > 
> > > What do you mean by "driver init"?  module_init()?
> > > 
> > > No driver should be touching hardware in their module init call.  They
> > > should only be touching it in the probe callback as that is the only
> > > time they are ever allowed to talk to hardware.  Specifically the device
> > > that has been handed to them.
> > > 
> > > If there are in-kernel PCI drivers that do not do this, they need to be
> > > fixed today.
> > > 
> > > We don't care about out-of-tree drivers for obvious reasons that we have
> > > no control over them.
> > > 
> > > thanks,
> > > 
> > > greg k-h
> > 
> > Well talk to Andi about it pls :)
> > https://lore.kernel.org/r/ad1e41d1-3f4e-8982-16ea-18a3b2c04019%40linux.intel.com
> 
> As Alan said, the minute you allow any driver to get into your kernel,
> it can do anything it wants to.
> 
> So just don't allow drivers to be added to your kernel if you care about
> these things.  The system owner has that mechanism today.
> 
> thanks,
> 
> greg k-h

The "it" that I referred to is the claim that no driver should be
touching hardware in their module init call. Andi seems to think
such drivers are worth working around with a special remap API.

-- 
MST