[Xen-devel] [PATCH] x86/vm_event: correctly gather gs_shadow value

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

Currently the gs_shadow value is only cached when the vCPU is being scheduled
out by Xen. Reporting this (usually) stale value through vm_event is incorrect,
since it doesn't represent the actual state of the vCPU at the time the event
was recorded. This prevents vm_event subscribers from correctly finding kernel
structures in the guest when it is trapped while in ring3.

Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/vm_event.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index 51c3493b1d..4464940da7 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -239,7 +239,7 @@ void vm_event_fill_regs(vm_event_request_t *req)
     vm_event_pack_segment_register(x86_seg_ds, &req->data.regs.x86);
     vm_event_pack_segment_register(x86_seg_es, &req->data.regs.x86);
 
-    req->data.regs.x86.shadow_gs = ctxt.shadow_gs;
+    req->data.regs.x86.shadow_gs = rdgsshadow();
     req->data.regs.x86.dr6 = ctxt.dr6;
 #endif
 }
-- 
2.20.1


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