[Xen-changelog] [xen master] x86/32on64: don't modify guest descriptors without need

[patchbot@xxxxxxx]

commit 82a9ae278ce6e76838066ab85bf0ace1d9e858bf
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Sep 30 16:45:46 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Sep 30 16:45:46 2016 +0200

    x86/32on64: don't modify guest descriptors without need
    
    System gates with type 0 shouldn't have what might be their DPL altered
    - such descriptors can't be used anyway without incurring a #GP, and
    hence adjusting its DPL is only risking to confuse the guest.
    
    Also bail right away for non-present descriptors - no need to write
    back anything in that case.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/x86_64/mm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
index 250d3e0..b8b6b70 100644
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -1088,7 +1088,7 @@ int check_descriptor(const struct domain *dom, struct 
desc_struct *d)
 
     /* A not-present descriptor will always fault, so is safe. */
     if ( !(b & _SEGMENT_P) ) 
-        goto good;
+        return 1;
 
     /* Check and fix up the DPL. */
     dpl = (b >> 13) & 3;
@@ -1130,7 +1130,7 @@ int check_descriptor(const struct domain *dom, struct 
desc_struct *d)
 
     /* Invalid type 0 is harmless. It is used for 2nd half of a call gate. */
     if ( (b & _SEGMENT_TYPE) == 0x000 )
-        goto good;
+        return 1;
 
     /* Everything but a call gate is discarded here. */
     if ( (b & _SEGMENT_TYPE) != 0xc00 )
--
generated by git-patchbot for /home/xen/git/xen.git#master

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