[PATCH 3.16 180/346] PM / hibernate: Restore processor state before using per-CPU variables

[Ben Hutchings]

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Garnier <thgarnie@xxxxxxxxxx>

commit 62822e2ec4ad091ba31f823f577ef80db52e3c2c upstream.

Restore the processor state before calling any other functions to
ensure per-CPU variables can be used with KASLR memory randomization.

Tracing functions use per-CPU variables (GS based on x86) and one was
called just before restoring the processor state fully. It resulted
in a double fault when both the tracing & the exception handler
functions tried to use a per-CPU variable.

Fixes: bb3632c6101b (PM / sleep: trace events for suspend/resume)
Reported-and-tested-by: Borislav Petkov <bp@xxxxxxx>
Reported-by: Jiri Kosina <jikos@xxxxxxxxxx>
Tested-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
Tested-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
Acked-by: Pavel Machek <pavel@xxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/power/hibernate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -301,12 +301,12 @@ static int create_image(int platform_mod
 	save_processor_state();
 	trace_suspend_resume(TPS("machine_suspend"), PM_EVENT_HIBERNATE, true);
 	error = swsusp_arch_suspend();
+	/* Restore control flow magically appears here */
+	restore_processor_state();
 	trace_suspend_resume(TPS("machine_suspend"), PM_EVENT_HIBERNATE, false);
 	if (error)
 		printk(KERN_ERR "PM: Error %d creating hibernation image\n",
 			error);
-	/* Restore control flow magically appears here */
-	restore_processor_state();
 	if (!in_suspend)
 		events_check_enabled = false;