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 <[e-mail]>
Signed-off-by: Souradeep <[e-mail]>
Signed-off-by: Srish Srinivasan <[e-mail]>
Tested-by: R Nageswara Sastry <[e-mail]>
Reviewed-by: Mimi Zohar <[e-mail]>
Reviewed-by: Stefan Berger <[e-mail]>
Reviewed-by: Nayna Jain <[e-mail]>
Reviewed-by: Andrew Donnellan <[e-mail]>
Signed-off-by: Madhavan Srinivasan <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

Documentation/ABI/testing/sysfs-secvar

···
 		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 <[e-mail]>

arch/powerpc/platforms/pseries/plpks-secvar.c

···
 		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",
···
 	return 0;
 }
 
-
-static const struct secvar_operations plpks_secvar_ops = {
+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,
+	.var_names = plpks_var_names_static,
+};
+
+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_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);