Subject: Re: [PATCH v7 1/8] powerpc: detect the secure boot mode of the system

From: Michael Ellerman <[email-masked]>
Date: Tue, 15 Oct 2019 22:30:21 +1100

Hi Nayna,

Just a few comments.

Nayna Jain <[email-masked]> writes:
> Secure boot on PowerNV defines different IMA policies based on the secure
> boot state of the system.

This description has got out of sync with what the patch does I think.
There's no IMA in here. I think you can just drop that sentence.

> This patch defines a function to detect the secure boot state of the
> system.

That's what the patch really does ^ - just make it clear that it's only
on powernv.

>
> The PPC_SECURE_BOOT config represents the base enablement of secureboot
> on POWER.

s/POWER/powerpc/.

>
> Signed-off-by: Nayna Jain <[email-masked]>
> ---
>  arch/powerpc/Kconfig                   | 10 ++++++
>  arch/powerpc/include/asm/secure_boot.h | 29 ++++++++++++++++++
>  arch/powerpc/kernel/Makefile           |  2 ++
>  arch/powerpc/kernel/secure_boot.c      | 42 ++++++++++++++++++++++++++
>  4 files changed, 83 insertions(+)
>  create mode 100644 arch/powerpc/include/asm/secure_boot.h
>  create mode 100644 arch/powerpc/kernel/secure_boot.c
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 3e56c9c2f16e..b4a221886fcf 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -934,6 +934,16 @@ config PPC_MEM_KEYS
>  
>  	  If unsure, say y.
>  
> +config PPC_SECURE_BOOT
> +	prompt "Enable secure boot support"
> +	bool
> +	depends on PPC_POWERNV
> +	help
> +	  Systems with firmware secure boot enabled needs to define security
                                                        ^
                                                     need
> +	  policies to extend secure boot to the OS. This config allows user
                                                                      ^
                                                                      a
> +	  to enable OS secure boot on systems that have firmware support for
> +	  it. If in doubt say N.
> +
>  endmenu
>  
>  config ISA_DMA_API
> diff --git a/arch/powerpc/include/asm/secure_boot.h b/arch/powerpc/include/asm/secure_boot.h
> new file mode 100644
> index 000000000000..23d2ef2f1f7b
> --- /dev/null
> +++ b/arch/powerpc/include/asm/secure_boot.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Secure boot definitions
> + *
> + * Copyright (C) 2019 IBM Corporation
> + * Author: Nayna Jain
> + */
> +#ifndef _ASM_POWER_SECURE_BOOT_H
> +#define _ASM_POWER_SECURE_BOOT_H
> +
> +#ifdef CONFIG_PPC_SECURE_BOOT
> +
> +bool is_powerpc_os_secureboot_enabled(void);
> +struct device_node *get_powerpc_os_sb_node(void);

This function is never used outside arch/powerpc/kernel/secure_boot.c
and so doesn't need to be public.

> +#else
> +
> +static inline bool is_powerpc_os_secureboot_enabled(void)
> +{

I know there's a distinction between firmware secureboot and OS
secureboot, but I don't think we need that baked into the name. So just
is_ppc_secureboot_enabled() would be fine.

> +	return false;
> +}
> +
> +static inline struct device_node *get_powerpc_os_sb_node(void)
> +{
> +	return NULL;
> +}
> +
> +#endif
> +#endif
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index a7ca8fe62368..e2a54fa240ac 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -161,6 +161,8 @@ ifneq ($(CONFIG_PPC_POWERNV)$(CONFIG_PPC_SVM),)
>  obj-y				+= ucall.o
>  endif
>  
> +obj-$(CONFIG_PPC_SECURE_BOOT)	+= secure_boot.o
> +
>  # Disable GCOV, KCOV & sanitizers in odd or sensitive code
>  GCOV_PROFILE_prom_init.o := n
>  KCOV_INSTRUMENT_prom_init.o := n
> diff --git a/arch/powerpc/kernel/secure_boot.c b/arch/powerpc/kernel/secure_boot.c
> new file mode 100644
> index 000000000000..0488dbcab6b9
> --- /dev/null
> +++ b/arch/powerpc/kernel/secure_boot.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 IBM Corporation
> + * Author: Nayna Jain
> + */
> +#include <linux/types.h>
> +#include <linux/of.h>
> +#include <asm/secure_boot.h>
> +
> +struct device_node *get_powerpc_os_sb_node(void)
> +{
> +	return of_find_compatible_node(NULL, NULL, "ibm,secvar-v1");
> +}

Given that's only used in this file, once, it should just be inlined
into its caller.

> +
> +bool is_powerpc_os_secureboot_enabled(void)
> +{
> +	struct device_node *node;
> +
> +	node = get_powerpc_os_sb_node();
> +	if (!node)
> +		goto disabled;
> +
> +	if (!of_device_is_available(node)) {
> +		pr_err("Secure variables support is in error state, fail secure\n");
> +		goto enabled;
> +	}
> +
> +	/*
> +	 * secureboot is enabled if os-secure-enforcing property exists,
> +	 * else disabled.
> +	 */
> +	if (!of_find_property(node, "os-secure-enforcing", NULL))

Using of_property_read_bool() is preferable.

> +		goto disabled;
> +
> +enabled:
> +	pr_info("secureboot mode enabled\n");
> +	return true;
> +
> +disabled:
> +	pr_info("secureboot mode disabled\n");
> +	return false;
> +}

You could make that tail a bit more concise by doing something like
below, but up to you:

	bool enabled = false;
        ...

	enabled = of_property_read_bool(node, "os-secure-enforcing");
out:
	pr_info("secureboot mode %s\n", enabled ? "enabled" : "disabled");
	return enabled;
}

cheers