On Thu, Sep 30, 2021 at 10:43:05AM -0400, Alan Stern 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@xxxxxxxxx> > > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> > > > > > > > > > > > > So what e.g. the PCI patch > > > https://lore.kernel.org/all/CACK8Z6E8pjVeC934oFgr=VB3pULx_GyT2NkzAogdRQJ9TKSX9A@xxxxxxxxxxxxxx/ > > > 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. > > I don't see any point in talking about "untrusted drivers". If a > driver isn't trusted then it doesn't belong in your kernel. Period. > When you load a driver into your kernel, you are implicitly trusting > it (aside from limitations imposed by security modules). The code > it contains, the module_init code in particular, runs with full > superuser permissions. > > What use is there in loading a driver but telling the kernel "I don't > trust this driver, so don't allow it to probe any devices"? Why not > just blacklist it so that it never gets modprobed in the first place? > > Alan Stern When the driver is built-in, it seems useful to be able to block it without rebuilding the kernel. This is just flipping it around and using an allow-list for cases where you want to severly limit the available functionality. -- MST
