linux-kernel - Re: RFC: WMI Enhancements

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Date:   Thu, 13 Apr 2017 10:44:26 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Mario.Limonciello@...l.com
Cc:     Darren Hart <dvhart@...radead.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Michał Kępień <kernel@...pniu.pl>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>,
        Pali Rohár <pali.rohar@...il.com>,
        Corentin Chary <corentin.chary@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: RFC: WMI Enhancements

On Thu, Apr 13, 2017 at 10:39 AM,  <Mario.Limonciello@...l.com> wrote:
>> -----Original Message-----
>> From: Darren Hart [mailto:dvhart@...radead.org]
>> Sent: Thursday, April 13, 2017 12:06 PM
>> To: Limonciello, Mario <Mario_Limonciello@...l.com>
>> Cc: luto@...nel.org; kernel@...pniu.pl; rjw@...ysocki.net;
>> len.brown@...el.com; pali.rohar@...il.com; corentin.chary@...il.com;
>> andriy.shevchenko@...ux.intel.com; linux-kernel@...r.kernel.org; platform-
>> driver-x86@...r.kernel.org; linux-pm@...r.kernel.org
>> Subject: Re: RFC: WMI Enhancements
>>

> Well the "most" interesting to me is the SMBIOS calling interface on the
> regular Dell GUID (WMBA IIRC).  That's what is used to manipulate keyboard
> LED timeouts in dell-laptop (although through direct SMI today).
>
> It's also what is used for other SMBIOS calls like changing random BIOS settings
> that shouldn't be generically exposed in sysfs but should be controlled by
> manageability tools.
>
> Example: turning on/off legacy option ROM or changing legacy boot order.
>

IIUC we basically can't expose the SMI--based interface to this entry
point to userspace because of its use of physical addressing.  It is
reasonably safe to expose the WMI version?  (IOW should be expect that
it doesn't enable kernel-mode or SMM code execution?)

TBH, I've occasionally considered writing a driver to expose SMM code
execution on systems with a known reliable exploit :)