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

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

    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@xxxxxxxxxx>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 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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