powerpc/pseries: Restore default security feature flags on setup

After migration the security feature flags might have changed (e.g.,
destination system with unpatched firmware), but some flags are not
set/clear again in init_cpu_char_feature_flags() because it assumes
the security flags to be the defaults.

Additionally, if the H_GET_CPU_CHARACTERISTICS hypercall fails then
init_cpu_char_feature_flags() does not run again, which potentially
might leave the system in an insecure or sub-optimal configuration.

So, just restore the security feature flags to the defaults assumed
by init_cpu_char_feature_flags() so it can set/clear them correctly,
and to ensure safe settings are in place in case the hypercall fail.

Fixes: f636c14790ea ("powerpc/pseries: Set or clear security feature flags")
Depends-on: 19887d6a28e2 ("powerpc: Move default security feature flags")
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/setup.c

@@ -462,6 +462,10 @@ static void __init find_and_init_phbs(void)
 
 static void init_cpu_char_feature_flags(struct h_cpu_char_result *result)
 {
+	/*
+	 * The features below are disabled by default, so we instead look to see
+	 * if firmware has *enabled* them, and set them if so.
+	 */
 	if (result->character & H_CPU_CHAR_SPEC_BAR_ORI31)
 		security_ftr_set(SEC_FTR_SPEC_BAR_ORI31);
 
@@ -501,6 +505,13 @@ void pseries_setup_rfi_flush(void)
 	bool enable;
 	long rc;
 
+	/*
+	 * Set features to the defaults assumed by init_cpu_char_feature_flags()
+	 * so it can set/clear again any features that might have changed after
+	 * migration, and in case the hypercall fails and it is not even called.
+	 */
+	powerpc_security_features = SEC_FTR_DEFAULT;
+
 	rc = plpar_get_cpu_characteristics(&result);
 	if (rc == H_SUCCESS)
 		init_cpu_char_feature_flags(&result);