From 82a9ae278ce6e76838066ab85bf0ace1d9e858bf Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Fri, 30 Sep 2016 16:45:46 +0200 Subject: [PATCH] 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 Reviewed-by: Andrew Cooper --- 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 250d3e0025..b8b6b70a06 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 ) -- 2.39.5