powerpc/pseries: Restore default security feature flags on setup

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>