linux-kernel - Re: [PATCH V2 1/3] efi: Support for MOK variable config table

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Date:   Thu, 1 Oct 2020 22:57:07 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Lenny Szubowicz <lszubowi@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        linux-security-module@...r.kernel.org, andy.shevchenko@...il.com,
        James Morris <jmorris@...ei.org>, serge@...lyn.com,
        Kees Cook <keescook@...omium.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Borislav Petkov <bp@...en8.de>,
        Peter Jones <pjones@...hat.com>,
        David Howells <dhowells@...hat.com>, prarit@...hat.com
Subject: Re: [PATCH V2 1/3] efi: Support for MOK variable config table

On Thu, 1 Oct 2020 at 19:44, Nathan Chancellor <natechancellor@...il.com> wrote:
>
> On Fri, Sep 04, 2020 at 09:31:05PM -0400, Lenny Szubowicz wrote:
> > Because of system-specific EFI firmware limitations, EFI volatile
> > variables may not be capable of holding the required contents of
> > the Machine Owner Key (MOK) certificate store when the certificate
> > list grows above some size. Therefore, an EFI boot loader may pass
> > the MOK certs via a EFI configuration table created specifically for
> > this purpose to avoid this firmware limitation.
> >
> > An EFI configuration table is a much more primitive mechanism
> > compared to EFI variables and is well suited for one-way passage
> > of static information from a pre-OS environment to the kernel.
> >
> > This patch adds initial kernel support to recognize, parse,
> > and validate the EFI MOK configuration table, where named
> > entries contain the same data that would otherwise be provided
> > in similarly named EFI variables.
> >
> > Additionally, this patch creates a sysfs binary file for each
> > EFI MOK configuration table entry found. These files are read-only
> > to root and are provided for use by user space utilities such as
> > mokutil.
> >
> > A subsequent patch will load MOK certs into the trusted platform
> > key ring using this infrastructure.
> >
> > Signed-off-by: Lenny Szubowicz <lszubowi@...hat.com>
>
> I have not seen this reported yet but this breaks arm allyesconfig and
> allmodconfig when CPU_LITTLE_ENDIAN is force selected (because CONFIG_EFI
> will actually be enabled):
>
> $ cat le.config
> CONFIG_CPU_BIG_ENDIAN=n
>
> $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- KCONFIG_ALLCONFIG=le.config allyesconfig drivers/firmware/efi/mokvar-table.o
> drivers/firmware/efi/mokvar-table.c: In function 'efi_mokvar_table_init':
> drivers/firmware/efi/mokvar-table.c:139:5: error: implicit declaration of function 'early_memunmap' [-Werror=implicit-function-declaration]
>   139 |     early_memunmap(va, map_size);
>       |     ^~~~~~~~~~~~~~
> drivers/firmware/efi/mokvar-table.c:148:9: error: implicit declaration of function 'early_memremap' [-Werror=implicit-function-declaration]
>   148 |    va = early_memremap(efi.mokvar_table, map_size);
>       |         ^~~~~~~~~~~~~~
> drivers/firmware/efi/mokvar-table.c:148:7: warning: assignment to 'void *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
>   148 |    va = early_memremap(efi.mokvar_table, map_size);
>       |       ^
> cc1: some warnings being treated as errors
> make[4]: *** [scripts/Makefile.build:283: drivers/firmware/efi/mokvar-table.o] Error 1
>
> Cheers,
> Nathan

Hi Nathan,

Does adding

#include <asm/early_ioremap.h>

to drivers/firmware/efi/mokvar-table.c fix the issue?