powerpc/configs/skiroot: Enable security features

This turns on HARDENED_USERCOPY with HARDENED_USERCOPY_PAGESPAN, and
FORTIFY_SOURCE.

It also enables SECURITY_LOCKDOWN_LSM with _EARLY and
LOCK_DOWN_KERNEL_FORCE_INTEGRITY options enabled. This still allows
xmon to be used in read-only mode.

MODULE_SIG is selected by lockdown, so it is still enabled.

Because we're setting LOCK_DOWN_KERNELFORCE_INTEGRITY=y we also need
to enable KEXEC_FILE=y so that kexec continues to work.

Signed-off-by: Joel Stanley <joel@jms.id.au>
[mpe: Switch to lockdown integrity mode per oohal, enable KEXEC_FILE
      as reported by jms]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200121043000.16212-7-mpe@ellerman.id.au

arch/powerpc/configs/skiroot_defconfig

@@ -36,6 +36,7 @@ CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
 CONFIG_CPU_IDLE=y
 CONFIG_HZ_100=y
 CONFIG_KEXEC=y
+CONFIG_KEXEC_FILE=y
 CONFIG_PRESERVE_FA_DUMP=y
 CONFIG_IRQ_ALL_CPUS=y
 CONFIG_NUMA=y
@@ -49,7 +50,6 @@ CONFIG_JUMP_LABEL=y
 CONFIG_STRICT_KERNEL_RWX=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
-CONFIG_MODULE_SIG=y
 CONFIG_MODULE_SIG_FORCE=y
 CONFIG_MODULE_SIG_SHA512=y
 CONFIG_PARTITION_ADVANCED=y
@@ -272,6 +272,16 @@ CONFIG_NLS_ASCII=y
 CONFIG_NLS_ISO8859_1=y
 CONFIG_NLS_UTF8=y
 CONFIG_ENCRYPTED_KEYS=y
+CONFIG_SECURITY=y
+CONFIG_HARDENED_USERCOPY=y
+# CONFIG_HARDENED_USERCOPY_FALLBACK is not set
+CONFIG_HARDENED_USERCOPY_PAGESPAN=y
+CONFIG_FORTIFY_SOURCE=y
+CONFIG_SECURITY_LOCKDOWN_LSM=y
+CONFIG_SECURITY_LOCKDOWN_LSM_EARLY=y
+CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY=y
+# CONFIG_INTEGRITY is not set
+CONFIG_LSM="yama,loadpin,safesetid,integrity"
 # CONFIG_CRYPTO_HW is not set
 CONFIG_CRC16=y
 CONFIG_CRC_ITU_T=y