linux-kernel - [PATCH 29 of 36] Use __KERNEL_DS as SS when returning to a kernel thread (VERIFY)

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Date:	Wed, 25 Jun 2008 00:19:25 -0400
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	xen-devel <xen-devel@...ts.xensource.com>,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>, x86@...nel.org
Subject: [PATCH 29 of 36] Use __KERNEL_DS as SS when returning to a kernel
	thread (VERIFY)

    This is needed when the kernel is running on RING3, such as under Xen.
    x86_64 has a weird feature that makes it #GP on iret when SS is a null
    descriptor.

    This need to be tested on bare metal to make sure it doesn't cause any
    problems. AMD specs say SS is always ignored (except on iret?).

Signed-off-by: Eduardo Habkost <ehabkost@...hat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/kernel/entry_64.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -212,7 +212,7 @@
 	.macro FAKE_STACK_FRAME child_rip
 	/* push in order ss, rsp, eflags, cs, rip */
 	xorl %eax, %eax
-	pushq %rax /* ss */
+	pushq $__KERNEL_DS /* ss */
 	CFI_ADJUST_CFA_OFFSET	8
 	/*CFI_REL_OFFSET	ss,0*/
 	pushq %rax /* rsp */


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