linux-kernel - Re: [PATCH 02/16] efi: Get the secure boot status

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Date:   Mon, 21 Nov 2016 16:17:58 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     David Howells <dhowells@...hat.com>, Linn Crosetto <linn@....com>,
        keyrings@...r.kernel.org,
        Matthew Garrett <matthew.garrett@...ula.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/16] efi: Get the secure boot status

On Mon, Nov 21, 2016 at 01:14:52PM +0000, Ard Biesheuvel wrote:
> On 21 November 2016 at 12:41, David Howells <dhowells@...hat.com> wrote:
> > Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> >> > Looking in efi_get_secureboot(), is there a reason:
> >> >
> >> >         efi_guid_t var_guid = EFI_GLOBAL_VARIABLE_GUID;
> >> >
> >> > isn't static const?
> >>
> >> Not a good one, no. It used to be static const, but for some reason,
> >> commit 30d7bf034c03 ("efi/arm64: Check SetupMode when determining
> >> Secure Boot status") removed the static and the const (and I reviewed
> >> it and did not complain AFAIR)
> >> I'll gladly take a patch that reinstates that, though.
> >
> > Also, is there a reason that:
> >
> > typedef efi_status_t efi_get_variable_t (efi_char16_t *name, efi_guid_t *vendor, u32 *attr,
> >                                          unsigned long *data_size, void *data);
> >
> > Doesn't have const name and vendor?
> 
> Yes, but not a good one either.
> 
> Sadly, the prototypes in the UEFI spec completely ignore constness,
> and these definitions are intended to be identical to the ones in the
> spec. This also means, for instance, that most UEFI firmwares stores
> these kinds of GUIDs in read-write memory, which is a potential
> goldmine for hackers, given how GUIDs are UEFI's duct tape, i.e.,
> keeping the world together.

But the spec declares these two parameters as "IN", so it would seem
legal to declare them const, no?

Incidentally I've already prepared commits a couple of days ago to
change the GUID declarations to const everywhere and also change the
get_variable prototype, I was planning to submit them for 4.11... :-)

Thanks,

Lukas