linux-kernel - Re: [PATCH v2 2/3] powerpc/secvar: Expose secvars relevant to the key management mode

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Message-ID: <aDATahmPIsOmiFAK@kitsune.suse.cz>
Date: Fri, 23 May 2025 08:19:22 +0200
From: Michal Suchánek <msuchanek@...e.de>
To: Srish Srinivasan <ssrish@...ux.ibm.com>
Cc: linux-integrity@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
	christophe.leroy@...roup.eu, naveen@...nel.org, ajd@...ux.ibm.com,
	zohar@...ux.ibm.com, nayna@...ux.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] powerpc/secvar: Expose secvars relevant to the
 key management mode

Hello,

On Wed, May 21, 2025 at 04:27:58PM +0530, Srish Srinivasan wrote:
> The PLPKS enabled PowerVM LPAR sysfs exposes all of the secure boot
> secvars irrespective of the key management mode.
> 
> The PowerVM LPAR supports static and dynamic key management for secure
> boot. The key management option can be updated in the management
> console. Only in the dynamic key mode can the user modify the secure
> boot secvars db, dbx, grubdb, grubdbx, and sbat, which are exposed via
> the sysfs interface. But the sysfs interface exposes these secvars even
> in the static key mode. This could lead to errors when reading them or
> writing to them in the static key mode.

would it cause an error when reading these variables or only when
writing them?

Thanks

Michal


> 
> Expose only PK, trustedcadb, and moduledb in the static key mode to
> enable loading of signed third-party kernel modules.
> 
> Co-developed-by: Souradeep <soura@...p.linux.ibm.com>
> Signed-off-by: Souradeep <soura@...p.linux.ibm.com>
> Signed-off-by: Srish Srinivasan <ssrish@...ux.ibm.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
> Reviewed-by: Nayna Jain <nayna@...ux.ibm.com>
> Reviewed-by: Andrew Donnellan <ajd@...ux.ibm.com>
> ---
>  Documentation/ABI/testing/sysfs-secvar        |  6 ++++
>  arch/powerpc/platforms/pseries/plpks-secvar.c | 28 ++++++++++++++++---
>  2 files changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-secvar b/Documentation/ABI/testing/sysfs-secvar
> index 45281888e520..948df3446a03 100644
> --- a/Documentation/ABI/testing/sysfs-secvar
> +++ b/Documentation/ABI/testing/sysfs-secvar
> @@ -37,6 +37,12 @@ Description:	Each secure variable is represented as a directory named as
>  		representation. The data and size can be determined by reading
>  		their respective attribute files.
>  
> +		Only secvars relevant to the key management mode are exposed.
> +		Only in the dynamic key mode can the user modify the secure boot
> +		secvars db, dbx, grubdb, grubdbx, and sbat. PK, trustedcadb and
> +		moduledb are the secvars common to both static and dynamic key
> +		management modes.
> +
>  What:		/sys/firmware/secvar/vars/<variable_name>/size
>  Date:		August 2019
>  Contact:	Nayna Jain <nayna@...ux.ibm.com>
> diff --git a/arch/powerpc/platforms/pseries/plpks-secvar.c b/arch/powerpc/platforms/pseries/plpks-secvar.c
> index 767e5e8c6990..f9e9cc40c9d0 100644
> --- a/arch/powerpc/platforms/pseries/plpks-secvar.c
> +++ b/arch/powerpc/platforms/pseries/plpks-secvar.c
> @@ -59,7 +59,14 @@ static u32 get_policy(const char *name)
>  		return PLPKS_SIGNEDUPDATE;
>  }
>  
> -static const char * const plpks_var_names[] = {
> +static const char * const plpks_var_names_static[] = {
> +	"PK",
> +	"moduledb",
> +	"trustedcadb",
> +	NULL,
> +};
> +
> +static const char * const plpks_var_names_dynamic[] = {
>  	"PK",
>  	"KEK",
>  	"db",
> @@ -213,21 +220,34 @@ static int plpks_max_size(u64 *max_size)
>  	return 0;
>  }
>  
> +static const struct secvar_operations plpks_secvar_ops_static = {
> +	.get = plpks_get_variable,
> +	.set = plpks_set_variable,
> +	.format = plpks_secvar_format,
> +	.max_size = plpks_max_size,
> +	.config_attrs = config_attrs,
> +	.var_names = plpks_var_names_static,
> +};
>  
> -static const struct secvar_operations plpks_secvar_ops = {
> +static const struct secvar_operations plpks_secvar_ops_dynamic = {
>  	.get = plpks_get_variable,
>  	.set = plpks_set_variable,
>  	.format = plpks_secvar_format,
>  	.max_size = plpks_max_size,
>  	.config_attrs = config_attrs,
> -	.var_names = plpks_var_names,
> +	.var_names = plpks_var_names_dynamic,
>  };
>  
>  static int plpks_secvar_init(void)
>  {
> +	u8 mode;
> +
>  	if (!plpks_is_available())
>  		return -ENODEV;
>  
> -	return set_secvar_ops(&plpks_secvar_ops);
> +	mode = plpks_get_sb_keymgmt_mode();
> +	if (mode)
> +		return set_secvar_ops(&plpks_secvar_ops_dynamic);
> +	return set_secvar_ops(&plpks_secvar_ops_static);
>  }
>  machine_device_initcall(pseries, plpks_secvar_init);
> -- 
> 2.47.1
> 
>