powerpc/secvar: Expose secvars relevant to the key management mode

JIRA: https://issues.redhat.com/browse/RHEL-101962

commit c1d96cd
Author: Srish Srinivasan <ssrish@linux.ibm.com>
Date:   Wed Jun 11 02:49:06 2025 +0530

    powerpc/secvar: Expose secvars relevant to the key management mode

    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. The secvars PK, trustedcadb, and moduledb can be consumed both
    in the static and dynamic key management modes for the loading of signed
    third-party kernel modules. However, other secvars i.e. KEK, grubdb,
    grubdbx, sbat, db and dbx, which are used to verify the grub and kernel
    images, are consumed only in the dynamic key management mode.

    Expose only PK, trustedcadb, and moduledb in the static key management
    mode.

    Co-developed-by: Souradeep <soura@imap.linux.ibm.com>
    Signed-off-by: Souradeep <soura@imap.linux.ibm.com>
    Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
    Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>
    Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
    Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
    Reviewed-by: Nayna Jain <nayna@linux.ibm.com>
    Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
    Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
    Link: https://patch.msgid.link/20250610211907.101384-3-ssrish@linux.ibm.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

Documentation/ABI/testing/sysfs-secvar

@@ -34,6 +34,13 @@ 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 management mode should the user have
+		access (read and write) to the secure boot secvars db, dbx,
+		grubdb, grubdbx, and sbat. These secvars are not consumed in the
+		static key management mode. 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@linux.ibm.com>

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",
@@ -197,21 +204,34 @@ 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);