On Thursday 21 September 2017 08:57:05 Mario Limonciello wrote: > The existing way that the dell-smbios helper module and associated > other drivers (dell-laptop, dell-wmi) communicate with the platform > really isn't secure. It requires creating a buffer in physical > DMA32 memory space and passing that to the platform via SMM. > > Since the platform got a physical memory pointer, you've just got > to trust that the platform has only modified (and accessed) memory > within that buffer. And what is the problem? The whole memory management is done by kernel itself, so you already need to trust it. > Dell Platform designers recognize this security risk and offer a > safer way to communicate with the platform over ACPI. This is > in turn exposed via a WMI interface to the OS. Hm... I cannot understand how some proprietary ACPI bytecode interpreted by kernel can be safer as kernel code itself. Can you describe more details about this security risk? > When communicating over WMI-ACPI the communication doesn't occur > with physical memory pointers. When the ASL is invoked, the fixed > length ACPI buffer is copied to a small operating region. The ASL > will invoke the SMI, and SMM will only have access to this operating > region. When the ASL returns the buffer is copied back for the OS > to process. If problem is in current kernel implementation, then it can be fixed. I'm not against using new WMI communication, but I cannot understand how kernel code itself is less safer as some other code which is interpreted by kernel. It does not make sense for me. > This method of communication should also deprecate the usage of the > dcdbas kernel module and software dependent upon it's interface. > Instead offer a syfs interface for communicating with this ASL > method to allow userspace to use instead. > > To faciliate that needs for userspace and kernel space this patch > series introduces a generic way for WMI drivers to be able to > create character devices through the WMI bus when desired. > Requiring WMI drivers to explictly ask for this functionality will > act as an effective vendor whitelist. -- Pali Rohár pali.rohar@xxxxxxxxx
