[tip:x86/asm] x86/entry/32: Fix FS and GS restore in opportunistic SYSEXIT

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  3bd29515d1cad26fa85a1a9b442de8816c1f5c54
Gitweb:     http://git.kernel.org/tip/3bd29515d1cad26fa85a1a9b442de8816c1f5c54
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Fri, 16 Oct 2015 15:42:55 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sun, 18 Oct 2015 12:11:16 +0200

x86/entry/32: Fix FS and GS restore in opportunistic SYSEXIT

We either need to restore them before popping and thus changing
ESP, or we need to adjust the offsets.  The former is simpler.

Reported-and-tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 5f310f739b4c x86/entry/32: ("Re-implement SYSENTER using the new C path")
Link: http://lkml.kernel.org/r/461e5c7d8fa3821529893a4893ac9c4bc37f9e17.1445035014.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/entry/entry_32.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 4f97f49..3eb572e 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -315,14 +315,14 @@ sysenter_past_esp:
 	TRACE_IRQS_ON			/* User mode traces as IRQs on. */
 	movl	PT_EIP(%esp), %edx	/* pt_regs->ip */
 	movl	PT_OLDESP(%esp), %ecx	/* pt_regs->sp */
+1:	mov	PT_FS(%esp), %fs
+	PTGS_TO_GS
 	popl	%ebx			/* pt_regs->bx */
 	addl	$2*4, %esp		/* skip pt_regs->cx and pt_regs->dx */
 	popl	%esi			/* pt_regs->si */
 	popl	%edi			/* pt_regs->di */
 	popl	%ebp			/* pt_regs->bp */
 	popl	%eax			/* pt_regs->ax */
-1:	mov	PT_FS(%esp), %fs
-	PTGS_TO_GS
 
 	/*
 	 * Return back to the vDSO, which will pop ecx and edx.