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>
(cherry picked from commit 6232774f1599028a15418179d17f7df47ede770a)

CVE-2018-3639 (powerpc)

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index e6d707df7ecf35ab99d0250bf0e1518b713405e9..beb1f6fab44ea7b4806a600875f47b99fe6daa72 100644 (file)
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -458,6 +458,10 @@ 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);
 
@@ -497,6 +501,13 @@ static 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);