On Thu, Aug 13, 2020 at 11:40 PM Daniel Gutson <[email protected]> wrote: > > On Thu, Aug 13, 2020 at 12:41 PM Arnd Bergmann <[email protected]> wrote: > > > > On Tue, Aug 4, 2020 at 11:26 PM Daniel Gutson <[email protected]> wrote: > > > On Tue, Aug 4, 2020 at 5:46 PM Arnd Bergmann <[email protected]> wrote: > > > > > But wait, Mika, the author of the file, asked earlier not to remove > > > > > the module parameter of intel-spi, and just remove the unconditional > > > > > attempt to turn the chip writable in intle-spi-pci. > > > > > > > > Yes, and I think that is fine (aside from the inconsistency with bay > > > > trail > > > > that you have not commented on), > > > > > > There are two inconsistencies before any of my patches: > > > 1) in intel-spi.c: uses the module parameter only for bay trail. > > > 2) intel-spi.c uses a module parameter whereas intel-spi-pci doesn't > > > > Neither of these matches what I see in the source code. Please > > check again. > > > > Once more: intel-spi.c has a module parameter that controls writing > > to the device regardless of the back-end (platform or pci), purely > > in software. > > If I understand you correctly, this is not what I see: > If the deviceID is listed in intel-spi-pci.c > (https://elixir.bootlin.com/linux/latest/source/drivers/mtd/spi-nor/controllers/intel-spi-pci.c#L66) > then intel_spi_pci_probe will be called, where it unconditionally will > try to make the chip writable > https://elixir.bootlin.com/linux/latest/source/drivers/mtd/spi-nor/controllers/intel-spi-pci.c#L44 > These devices correspond to the BXT and CNL devices (lines 19 and 23 resp.). > > Lines later (53), it will call intel-spi.c 's intel_spi_probe > function, which ends up calling intel_spi_init, > which checks for the type > (https://elixir.bootlin.com/linux/latest/source/drivers/mtd/spi-nor/controllers/intel-spi.c#L313) > It is in this switch where the module parameter is checked, but only > in the BYT case; however, > flow coming from intel-spi-pci is BXT and CNL as mentioned before, > landing in their case labels (lines 343 and 351 respectively) > where the module parameter is not checked. > > Therefore, for BXT and CNL probed in intel-spi-pci, the chip is turned > writable and later the module parameter is not honored.
The module parameter is definitely honored on all hardware, but the driver only cares about the functionality it provides through the mtd interface: https://elixir.bootlin.com/linux/latest/source/drivers/mtd/spi-nor/controllers/intel-spi.c#L941 If you care about other (malicious) code writing to the driver, please explain what the specific attack scenario is that you are worried about, and why you think this is not sufficient. What code would be able to write to the device if not the device driver itself? Arnd
