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

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Date:   Thu, 1 Oct 2020 10:44:36 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Lenny Szubowicz <lszubowi@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-security-module@...r.kernel.org, andy.shevchenko@...il.com,
        ardb@...nel.org, jmorris@...ei.org, serge@...lyn.com,
        keescook@...omium.org, zohar@...ux.ibm.com, bp@...en8.de,
        pjones@...hat.com, dhowells@...hat.com, prarit@...hat.com
Subject: Re: [PATCH V2 1/3] efi: Support for MOK variable config table

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