linux-kernel - [PATCH v2 2/2] x86/entry/32: Fix FS and GS restore in opportunistic SYSEXIT

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Date:	Fri, 16 Oct 2015 15:42:55 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 2/2] 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.

Fixes: 5f310f739b4c x86/entry/32: ("Re-implement SYSENTER using the new C path")
Signed-off-by: Andy Lutomirski <luto@...nel.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 ba0dad937be9..e3ede42d30e2 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -315,6 +315,8 @@ 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 */
 	popl	%eax			/* skip pt_regs->cx */
 	popl	%eax			/* skip pt_regs->dx */
@@ -322,8 +324,6 @@ sysenter_past_esp:
 	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.
-- 
2.4.3

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