linux-kernel - [PATCH v1] x86/power/64: Restore processor state before using per-cpu variables

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Date:	Thu, 11 Aug 2016 14:49:29 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	keescook@...omium.org, kernel-hardening@...ts.openwall.com,
	jikos@...nel.org, bpetkov@...e.de, yinghai@...nel.org,
	Thomas Garnier <thgarnie@...gle.com>
Subject: [PATCH v1] x86/power/64: Restore processor state before using per-cpu variables

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

Tracing functions use per-cpu variables (gs based) 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.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
Based on next-20160808

Thanks to Rafael, Jiri & Borislav in tracking down this bug.
---
 kernel/power/hibernate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index a881c6a..33c79b6 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -300,12 +300,12 @@ static int create_image(int platform_mode)
 	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;
 
-- 
2.8.0.rc3.226.g39d4020