From ffa64eff956a25548cad0391dbc14c672827be7b Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@kernel.org>
Date: Mon, 22 Jun 2015 14:40:03 +0200
Subject: [PATCH] x86: Load __USER_DS into DS/ES after resume

Srinivas Pandruvada reported a problem with system resume from
suspend-to-RAM on 32-bit x86 systems where the DS register of
the CPU is set to __KERNEL_DS instead of __USER_DS on return
to user space which cases a General Protection Fault to occur.

The issue is that DS is set to __KERNEL_DS by the ACPI resume code
path while the SYSEXIT path never reloads DS/ES.  It assumes they
are still __USER_DS set at the SYSENTER time (Brian Gerst), so if
the return to user space happens to be through SYSEXIT, it will lead
to the reported GPF.

Fix the problem by setting the DS and ES registers to __USER_DS
as expected by the SYSEXIT path.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=61781
Link: http://marc.info/?l=linux-pm&m=143406648920385&w=2
Acked-by: Pavel Machek <pavel@ucw.cz>
Tested-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Ingo Molnar <mingo@kernel.org>

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 arch/x86/kernel/acpi/wakeup_32.S | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/acpi/wakeup_32.S b/arch/x86/kernel/acpi/wakeup_32.S
index 665c6b7d2ea93..0c26b1b44e51a 100644
--- a/arch/x86/kernel/acpi/wakeup_32.S
+++ b/arch/x86/kernel/acpi/wakeup_32.S
@@ -12,11 +12,13 @@ ENTRY(wakeup_pmode_return)
 wakeup_pmode_return:
 	movw	$__KERNEL_DS, %ax
 	movw	%ax, %ss
-	movw	%ax, %ds
-	movw	%ax, %es
 	movw	%ax, %fs
 	movw	%ax, %gs
 
+	movw	$__USER_DS, %ax
+	movw	%ax, %ds
+	movw	%ax, %es
+
 	# reload the gdt, as we need the full 32 bit address
 	lidt	saved_idt
 	lldt	saved_ldt
-- 
2.39.5