Re: [PATCH] Lock down drivers that can have io ports, io mem, irqs and dma changed
From: Dominik Brodowski
Date: Tue Nov 22 2016 - 01:24:43 EST
On Mon, Nov 21, 2016 at 11:10:52PM +0000, David Howells wrote:
> One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> wrote:
> > You need to filter or lock down kernel module options because a lot of
> > modules let you set the I/O port or similar (eg mmio) which means you can
> > hack the entire machine with say the 8250 driver just by using it with an
> > mmio of the right location to patch the secure state to zero just by
> > getting the ability to write to the modules conf file.
> Is the attached patch the right sort of idea? [Note that I haven't actually
> compiled most of these drivers to check my changes yet.]
> commit 8613a9655dad98c3358d82a9c4310cebdcb852ae
> Author: David Howells <dhowells@xxxxxxxxxx>
> Date: Mon Nov 21 22:43:27 2016 +0000
> Lock down drivers that can have io ports, io mem, irqs and dma changed
> Lock down drivers that can have io ports, io mem, irqs and dma channels
> changed so that they can't be used to cause hardware to access the kernel
> (1) module_isa_driver() gets an extra parameter that, if true, will cause
> the module load to be rejected if the kernel is locked down.
> (2) module_driver() calls module_lockdown_check() to ask if the module
> load should be rejected if the kernel is locked down. This is a macro
> that should be #undef'd and then redefined right before
> module_driver() is called.
> (3) module_pci_driver() is a wrapper around module_driver(), so the same
> macro is used as in (2).
> (4) A number of drivers use parport 'ports' - so I haven't touched those.
You might also need to disable CIS overrides and CIS firmware loading for PCMCIA
drivers, I presume. That needs two changes:
- Abort in drivers/pcmcia/ds.c::pcmcia_load_firmware() or disable
the CONFIG_PCMCIA_LOAD_CIS config option permanently.
- Abort in drivers/pcmcia/cistpl.c::pccard_store_cis() or remove
write access to the "cis" file in