From 03617c188f41eeeb4223c919ee7e66e5a114f2c6 Mon Sep 17 00:00:00 2001 From: Gleb Natapov Date: Fri, 28 Jun 2013 13:17:18 +0300 Subject: [PATCH] KVM: VMX: mark unusable segment as nonpresent Some userspaces do not preserve unusable property. Since usable segment has to be present according to VMX spec we can use present property to amend userspace bug by making unusable segment always nonpresent. vmx_segment_access_rights() already marks nonpresent segment as unusable. Cc: stable@vger.kernel.org # 3.9+ Reported-by: Stefan Pietsch Tested-by: Stefan Pietsch Signed-off-by: Gleb Natapov Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index a7e1855..064d0be 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3404,15 +3404,22 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu, var->limit = vmx_read_guest_seg_limit(vmx, seg); var->selector = vmx_read_guest_seg_selector(vmx, seg); ar = vmx_read_guest_seg_ar(vmx, seg); + var->unusable = (ar >> 16) & 1; var->type = ar & 15; var->s = (ar >> 4) & 1; var->dpl = (ar >> 5) & 3; - var->present = (ar >> 7) & 1; + /* + * Some userspaces do not preserve unusable property. Since usable + * segment has to be present according to VMX spec we can use present + * property to amend userspace bug by making unusable segment always + * nonpresent. vmx_segment_access_rights() already marks nonpresent + * segment as unusable. + */ + var->present = !var->unusable; var->avl = (ar >> 12) & 1; var->l = (ar >> 13) & 1; var->db = (ar >> 14) & 1; var->g = (ar >> 15) & 1; - var->unusable = (ar >> 16) & 1; } static u64 vmx_get_segment_base(struct kvm_vcpu *vcpu, int seg) -- 2.7.4