linux-kernel - Re: [PATCH 5/7] efi: Get the secure boot status [ver #3]

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Message-ID: <17565.1480077303@warthog.procyon.org.uk>
Date:   Fri, 25 Nov 2016 12:35:03 +0000
From:   David Howells <dhowells@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     dhowells@...hat.com,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>, keyrings@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 5/7] efi: Get the secure boot status [ver #3]

Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:

> Yes. In pre-2.6, DeployedMode is not a reserved name, and so it may be
> possible for someone to slip in a DeployedMode=0 on a secure boot
> enabled system to trick the kernel into thinking lockdown should be
> disabled.

How does one get the version number?  Unfortunately, searching the document
for 'version' doesn't help as every page has that in the footer:-/

> > +               if (val == 1)
> > +                       return 0;
> 
> I think the logic is the wrong way around here. Secure Boot is enabled
> if SecureBoot=1 and SetupMode=0, unless DeployedMode=0. So you should
> return 0 here if val == 0, but only when running on 2.6 or later.

Good point.

David