linux-kernel - Re: [PATCH v10 1/9] powerpc: detect the secure boot mode of the system

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Message-Id: <09a57ae4-c7b1-aaf4-0f89-a0d7ed16f6cf@linux.ibm.com>
Date:   Mon, 4 Nov 2019 23:14:25 -0600
From:   Eric Richter <erichte@...ux.ibm.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>, linuxppc-dev@...abs.org,
        linux-efi@...r.kernel.org, linux-integrity@...r.kernel.org
Cc:     Nayna Jain <nayna@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jeremy Kerr <jk@...abs.org>,
        "Oliver O'Halloran" <oohall@...il.com>
Subject: Re: [PATCH v10 1/9] powerpc: detect the secure boot mode of the
 system

On 10/30/19 10:31 PM, Mimi Zohar wrote:
> From: Nayna Jain <nayna@...ux.ibm.com>
> 
> This patch defines a function to detect the secure boot state of a
> PowerNV system.
> 
> The PPC_SECURE_BOOT config represents the base enablement of secure boot
> for powerpc.
> 
> Signed-off-by: Nayna Jain <nayna@...ux.ibm.com>
> ---
>  arch/powerpc/Kconfig                   | 10 ++++++++++
>  arch/powerpc/include/asm/secure_boot.h | 23 +++++++++++++++++++++++
>  arch/powerpc/kernel/Makefile           |  2 ++
>  arch/powerpc/kernel/secure_boot.c      | 32 ++++++++++++++++++++++++++++++++
>  4 files changed, 67 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..56ea0019b616 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 need to define security
> +	  policies to extend secure boot to the OS. This config allows a user
> +	  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..07d0fe0ca81f
> --- /dev/null
> +++ b/arch/powerpc/include/asm/secure_boot.h
> @@ -0,0 +1,23 @@
> +/* 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_ppc_secureboot_enabled(void);
> +
> +#else
> +
> +static inline bool is_ppc_secureboot_enabled(void)
> +{
> +	return false;
> +}
> +
> +#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..63dc82c50862
> --- /dev/null
> +++ b/arch/powerpc/kernel/secure_boot.c
> @@ -0,0 +1,32 @@
> +// 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>
> +
> +bool is_ppc_secureboot_enabled(void)
> +{
> +	struct device_node *node;
> +	bool enabled = false;
> +
> +	node = of_find_compatible_node(NULL, NULL, "ibm,secvar-v1");

Per skiboot changes, should instead look for "ibm,secureboot".

Updated set can be found here:
https://patchwork.ozlabs.org/project/skiboot/list/?series=140626

> +	if (!of_device_is_available(node)) {
> +		pr_err("Cannot find secure variable node in device tree; failing to secure state\n");

The default value for "enabled" is false, so it's actually failing insecure. Although, the print is
probably unnecessary.

> +		goto out;
> +	}
> +
> +	/*
> +	 * secureboot is enabled if os-secure-enforcing property exists,
> +	 * else disabled.
> +	 */
> +	enabled = of_property_read_bool(node, "os-secure-enforcing");

Property has been renamed to "os-secureboot-enforcing".

> +> +out:
> +	of_node_put(node);
> +
> +	pr_info("Secure boot mode %s\n", enabled ? "enabled" : "disabled");
> +	return enabled;
> +}
>