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From: Florian Weimer <fw@deneb.enyo.de>
To: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Chris Friesen <chris.friesen@genband.com>,
        Greg KH <gregkh@linuxfoundation.org>,
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Subject: Re: [GIT PULL] Load keys from signed PE binaries
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Date: Thu, 28 Feb 2013 21:23:45 +0100
In-Reply-To: <20130228195321.GA8769@srcf.ucam.org> (Matthew Garrett's message
	of "Thu, 28 Feb 2013 19:53:21 +0000")
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* Matthew Garrett:

> On Thu, Feb 28, 2013 at 08:41:13PM +0100, Florian Weimer wrote:
>> * Matthew Garrett:
>> 
>> >> Would it be possible to have a signed bootloader that allows booting
>> >> Win8 from within the secure environment, or it could exit the secure
>> >> environment and run unsigned grub?
>> >
>> > What would stop the unsigned grub from installing a firmware hook that 
>> > lies about whether or not Secure Boot is enabled, and then booting 
>> > Windows?
>> 
>> Windows would not have access to the product key because it is stored
>> in a variable without EFI_VARIABLE_RUNTIME_ACCESS, so WGA and other
>> checks will fail, and the user will notice.
>
> grub's running before ExitBootServices(), because otherwise it has no 
> way to actually read anything off disk. Or draw to the screen.

Sorry, if Linux can read from the disk after ExitBootServices(), so
can a boot loader.  Actually, we could boot Linux directly, with an
initrd which contains a boot selector, and use kexec if the chosen
kernel doesn't match the initial one.