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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Fri, 16 Feb 2018 11:18:12 +0000
Message-ID: <CAKv+Gu_SD6yWJMGbTwGUWXtrgZKPkpANNaGe1PUruTG9j0yhcg@mail.gmail.com>
Subject: Re: [PATCH 0/2] efivars: reading variables can generate SMIs
To:     Borislav Petkov <bp@alien8.de>
Cc:     Joe Konno <joe.konno@linux.intel.com>,
        Matthew Garrett <mjg59@google.com>,
        Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@kernel.org>, linux-efi@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jeremy Kerr <jk@ozlabs.org>, Andi Kleen <ak@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Benjamin Drung <benjamin.drung@profitbricks.com>,
        Peter Jones <pjones@redhat.com>
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On 16 February 2018 at 11:08, Borislav Petkov <bp@alien8.de> wrote:
> On Fri, Feb 16, 2018 at 10:58:47AM +0000, Ard Biesheuvel wrote:
>> By your own reasoning above, that's a no-no as well.
>
> I'm sure we can come up with some emulation - the same way we did the
> BIOS emulation.
>
>> But thanks for your input. Anyone else got something constructive to contribute?
>
> The not-breaking userspace is constructive contribution. The last
> paragraph is my usual rant.
>

Fair enough. And I am not disagreeing with you either.

So question to Joe: is it well defined which variables may exhibit
this behavior? Given that UEFI variables are GUID scoped, would
whitelisting certain GUIDs (the ones userland currently relies on to
be readable my non-privileged users) and making everything else
user-only solve this problem as well?