[Xen-changelog] [xen stable-4.9] x86: fix GS-base-dirty determination

[patchbot@xxxxxxx]

commit df07ad1315e4d91f758b1e1e9b3cbd393146956f
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Nov 16 11:41:44 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Nov 16 11:41:44 2017 +0100

    x86: fix GS-base-dirty determination
    
    load_segments() writes the two MSRs in their "canonical" positions
    (GS_BASE for the user base, SHADOW_GS_BASE for the kernel one) and uses
    SWAPGS to switch them around if the incoming vCPU is in kernel mode. In
    order to not leave a stale kernel address in GS_BASE when the incoming
    guest is in user mode, the check on the outgoing vCPU needs to be
    dependent upon the mode it is currently in, rather than blindly looking
    at the user base.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 91f85280b9b80852352fcad73d94ed29fafb88da
    master date: 2017-10-24 18:12:31 +0200
---
 xen/arch/x86/domain.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 5ebd447..765bc00 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1905,7 +1905,8 @@ static void save_segments(struct vcpu *v)
         if ( regs->gs & ~3 )
             v->arch.pv_vcpu.gs_base_user = 0;
     }
-    if ( v->arch.pv_vcpu.gs_base_user )
+    if ( v->arch.flags & TF_kernel_mode ? v->arch.pv_vcpu.gs_base_kernel
+                                        : v->arch.pv_vcpu.gs_base_user )
         dirty_segment_mask |= DIRTY_GS_BASE_USER;
 
     this_cpu(dirty_segment_mask) = dirty_segment_mask;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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