Re: [PATCH 1/5] efi: Move the x86 secure boot switch to generic code

Ard Biesheuvel
2017-05-19T14:00:32Z

First of all, apologies for taking so long to respond.

On 6 April 2017 at 13:49, David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> Move the switch-statement in x86's setup_arch() that inteprets the
> secure_boot boot parameter to generic code.
>
> Suggested-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> Signed-off-by: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>
> arch/x86/kernel/setup.c | 14 +-------------
> drivers/firmware/efi/Kconfig | 23 +++++++++++++++++++++++
> drivers/firmware/efi/Makefile | 3 ++-
> drivers/firmware/efi/secure_boot.c | 34 ++++++++++++++++++++++++++++++++++
> include/linux/efi.h | 6 ++++++
> 5 files changed, 66 insertions(+), 14 deletions(-)
> create mode 100644 drivers/firmware/efi/secure_boot.c
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 4bf0c8926a1c..b89979ffa6e5 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1178,19 +1178,7 @@ void __init setup_arch(char **cmdline_p)
> /* Allocate bigger log buffer */
> setup_log_buf(1);
>
> - if (efi_enabled(EFI_BOOT)) {
> - switch (boot_params.secure_boot) {
> - case efi_secureboot_mode_disabled:
> - pr_info("Secure boot disabled\n");
> - break;
> - case efi_secureboot_mode_enabled:
> - pr_info("Secure boot enabled\n");
> - break;
> - default:
> - pr_info("Secure boot could not be determined\n");
> - break;
> - }
> - }
> + efi_set_secure_boot(boot_params.secure_boot);
>
> reserve_initrd();
>
> diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
> index 2e78b0b96d74..4b902ffbfcf4 100644
> --- a/drivers/firmware/efi/Kconfig
> +++ b/drivers/firmware/efi/Kconfig
> @@ -84,6 +84,29 @@ config EFI_PARAMS_FROM_FDT
> config EFI_RUNTIME_WRAPPERS
> bool
>
> +config EFI_SECURE_BOOT
> + bool "Support UEFI Secure Boot and lock down the kernel in secure boot mode"
> + default n
> + help
> + UEFI Secure Boot provides a mechanism for ensuring that the firmware
> + will only load signed bootloaders and kernels. Secure boot mode may
> + be determined from EFI variables provided by the BIOS if not

Please replace 'the BIOS' with something more generic.

> + indicated by the boot parameters.
> +
> + Enabling this option turns on support for UEFI secure boot in the
> + kernel. This will result in various kernel facilities being locked
> + away from userspace if the kernel detects that it has been booted in
> + secure boot mode. If it hasn't been booted in secure boot mode, or
> + this cannot be determined, the lock down doesn't occur.
> +
> + The kernel facilities that get locked down include:
> + - Viewing or changing the kernel's memory
> + - Directly accessing ioports
> + - Directly specifying ioports and other hardware parameters to drivers
> + - Storing the kernel image unencrypted for hibernation
> + - Loading unsigned modules
> + - Kexec'ing unsigned images
> +
> config EFI_ARMSTUB
> bool
>
> diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> index ad67342313ed..65969f840685 100644
> --- a/drivers/firmware/efi/Makefile
> +++ b/drivers/firmware/efi/Makefile
> @@ -22,7 +22,8 @@ obj-$(CONFIG_EFI_FAKE_MEMMAP) += fake_mem.o
> obj-$(CONFIG_EFI_BOOTLOADER_CONTROL) += efibc.o
> obj-$(CONFIG_EFI_TEST) += test/
> obj-$(CONFIG_EFI_DEV_PATH_PARSER) += dev-path-parser.o
> -obj-$(CONFIG_APPLE_PROPERTIES) += apple-properties.o
> +obj-$(CONFIG_EFI_SECURE_BOOT) += secure_boot.o
> +obj-$(CONFIG_APPLE_PROPERTIES) += apple-properties.oo

Spurious change here

>
> arm-obj-$(CONFIG_EFI) := arm-init.o arm-runtime.o
> obj-$(CONFIG_ARM) += $(arm-obj-y)
> diff --git a/drivers/firmware/efi/secure_boot.c b/drivers/firmware/efi/secure_boot.c
> new file mode 100644
> index 000000000000..cf5bccae15e8
> --- /dev/null
> +++ b/drivers/firmware/efi/secure_boot.c

We have a file called secureboot.c in libstub/, so for consistency,
could you please drop the underscore?

> @@ -0,0 +1,34 @@
> +/* Core kernel secure boot support.
> + *
> + * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
> +
> +#include <linux/efi.h>
> +#include <linux/kernel.h>
> +#include <linux/printk.h>
> +
> +/*
> + * Decide what to do when UEFI secure boot mode is enabled.
> + */
> +void __init efi_set_secure_boot(enum efi_secureboot_mode mode)
> +{
> + if (efi_enabled(EFI_BOOT)) {
> + switch (mode) {
> + case efi_secureboot_mode_disabled:
> + pr_info("Secure boot disabled\n");
> + break;
> + case efi_secureboot_mode_enabled:
> + pr_info("Secure boot enabled\n");
> + break;
> + default:
> + pr_info("Secure boot could not be determined\n");
> + break;
> + }
> + }
> +}
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 94d34e0be24f..d8938a780290 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1488,6 +1488,12 @@ enum efi_secureboot_mode {
> };
> enum efi_secureboot_mode efi_get_secureboot(efi_system_table_t *sys_table);
>
> +#ifdef CONFIG_EFI_SECURE_BOOT
> +void __init efi_set_secure_boot(enum efi_secureboot_mode mode);
> +#else
> +static inline void efi_set_secure_boot(enum efi_secureboot_mode mode) {}
> +#endif
> +
> /*
> * Arch code can implement the following three template macros, avoiding
> * reptition for the void/non-void return cases of {__,}efi_call_virt():
>