linux-kernel - Re: [PATCH v10 00/15] Introduce support for Dell SMBIOS over WMI

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Date:   Thu, 9 Nov 2017 10:52:08 +0100
From:   Pavel Machek <pavel@....cz>
To:     Mario Limonciello <mario.limonciello@...l.com>
Cc:     dvhart@...radead.org, Andy Shevchenko <andy.shevchenko@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>, quasisec@...gle.com,
        pali.rohar@...il.com, rjw@...ysocki.net, mjg59@...gle.com,
        hch@....de, Greg KH <greg@...ah.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>
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.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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