linux-kernel - Re: [PATCH v3 2/2] arm64/efi: check SetupMode when determining Secure Boot status

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Date:	Fri, 4 Mar 2016 09:01:14 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Linn Crosetto <linn@....com>
Cc:	Matt Fleming <matt@...eblueprint.co.uk>,
	Roy Franz <roy.franz@...aro.org>,
	Ingo Molnar <mingo@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] arm64/efi: check SetupMode when determining Secure
 Boot status

On 3 March 2016 at 22:45, Linn Crosetto <linn@....com> wrote:
> According to the UEFI specification (version 2.5 Errata A, page 87):
>
>     The platform firmware is operating in secure boot mode if the value of
>     the SetupMode variable is 0 and the SecureBoot variable is set to 1. A
>     platform cannot operate in secure boot mode if the SetupMode variable
>     is set to 1.
>
> Check the value of the SetupMode variable when determining the state of
> Secure Boot. Minor cleanup, change sizeof to match kernel style guidelines.
>
> Signed-off-by: Linn Crosetto <linn@....com>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

> ---
> v2:
>  - Reformat quote from UEFI specification and note cleanup (Mark Rutland)
>  - Restructure code on top of changes in patch 1/2
>
>  drivers/firmware/efi/libstub/arm-stub.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
> index 1e98fb7..c049d41 100644
> --- a/drivers/firmware/efi/libstub/arm-stub.c
> +++ b/drivers/firmware/efi/libstub/arm-stub.c
> @@ -20,21 +20,39 @@
>
>  static int efi_get_secureboot(efi_system_table_t *sys_table_arg)
>  {
> -       static efi_guid_t const var_guid = EFI_GLOBAL_VARIABLE_GUID;
> -       static efi_char16_t const var_name[] = {
> +       static efi_char16_t const sb_var_name[] = {
>                 'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0 };
> +       static efi_char16_t const sm_var_name[] = {
> +               'S', 'e', 't', 'u', 'p', 'M', 'o', 'd', 'e', 0 };
>
> +       efi_guid_t var_guid = EFI_GLOBAL_VARIABLE_GUID;
>         efi_get_variable_t *f_getvar = sys_table_arg->runtime->get_variable;
> -       unsigned long size = sizeof(u8);
> -       efi_status_t status;
>         u8 val;
> +       unsigned long size = sizeof(val);
> +       efi_status_t status;
>
> -       status = f_getvar((efi_char16_t *)var_name, (efi_guid_t *)&var_guid,
> +       status = f_getvar((efi_char16_t *)sb_var_name, (efi_guid_t *)&var_guid,
>                           NULL, &size, &val);
>
> +       if (status != EFI_SUCCESS)
> +               goto out_efi_err;
> +
> +       if (val == 0)
> +               return 0;
> +
> +       status = f_getvar((efi_char16_t *)sm_var_name, (efi_guid_t *)&var_guid,
> +                         NULL, &size, &val);
> +
> +       if (status != EFI_SUCCESS)
> +               goto out_efi_err;
> +
> +       if (val == 1)
> +               return 0;
> +
> +       return 1;
> +
> +out_efi_err:
>         switch (status) {
> -       case EFI_SUCCESS:
> -               return val;
>         case EFI_NOT_FOUND:
>                 return 0;
>         case EFI_DEVICE_ERROR:
> --
> 2.1.4
>