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Date:   Thu, 9 Nov 2017 10:52:08 +0100
From:   Pavel Machek <>
To:     Mario Limonciello <>
Cc:, Andy Shevchenko <>,
        LKML <>,,
        Andy Lutomirski <>,,,,,, Greg KH <>,
        Alan Cox <>
Subject: Re: [PATCH v10 00/15] Introduce support for Dell SMBIOS over WMI

On Thu 2017-10-19 12:50:03, 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.
> 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.
> 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.

SMM has access anywhere it wants. This may be good idea, but
definitely not for "security" reasons.
(cesky, pictures)

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