x86/reboot: Secure Launch SEXIT support on reboot paths

If the MLE kernel is being powered off, rebooted or halted,
then SEXIT must be called. Note that the GETSEC[SEXIT] leaf
can only be called after a machine_shutdown() has been done on
these paths. The machine_shutdown() is not called on a few paths
like when poweroff action does not have a poweroff callback (into
ACPI code) or when an emergency reset is done. In these cases,
just the TXT registers are finalized but SEXIT is skipped.

Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>

Author: rossphilipson

arch/x86/kernel/reboot.c

@@ -13,6 +13,7 @@
 #include <linux/objtool.h>
 #include <linux/pgtable.h>
 #include <linux/kexec.h>
+#include <linux/slaunch.h>
 #include <acpi/reboot.h>
 #include <asm/io.h>
 #include <asm/apic.h>
@@ -778,6 +779,12 @@ static void native_machine_restart(char *__unused)
 
 	if (!reboot_force)
 		machine_shutdown();
+	/*
+	 * The comments for slaunch_finalize() provides the explanation for the
+	 * conditions required to do the SEXIT op reflected in the conditional
+	 * parameter do_sexit.
+	 */
+	slaunch_finalize(!reboot_force);
 	__machine_emergency_restart(0);
 }
 
@@ -788,6 +795,8 @@ static void native_machine_halt(void)
 
 	tboot_shutdown(TB_SHUTDOWN_HALT);
 
+	slaunch_finalize(1);
+
 	stop_this_cpu(NULL);
 }
 
@@ -796,8 +805,12 @@ static void native_machine_power_off(void)
 	if (kernel_can_power_off()) {
 		if (!reboot_force)
 			machine_shutdown();
+		slaunch_finalize(!reboot_force);
 		do_kernel_power_off();
+	} else {
+		slaunch_finalize(0);
 	}
+
 	/* A fallback in case there is no PM info available */
 	tboot_shutdown(TB_SHUTDOWN_HALT);
 }
@@ -825,6 +838,7 @@ void machine_shutdown(void)
 
 void machine_emergency_restart(void)
 {
+	slaunch_finalize(0);
 	__machine_emergency_restart(1);
 }