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    SubjectRe: [PATCH 00/12] Introduce support for Dell SMBIOS over WMI
    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@gmail.com

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