linux-kernel - [RFC] KVM: SVM: ignore type when setting segment registers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1496064244-14785-1-git-send-email-gi-oh.kim@profitbricks.com>
Date:   Mon, 29 May 2017 15:24:04 +0200
From:   Gioh Kim <gi-oh.kim@...fitbricks.com>
To:     andre.przywara@....com, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Gioh Kim <gi-oh.kim@...fitbricks.com>
Subject: [RFC] KVM: SVM: ignore type when setting segment registers

Current code sets unusable as 1 if present is 1 and type is 0.
In Long mode, type value in segment descriptor is ignored.
So I think type should be ignored when setting the segment registers,
if type means the descriptor type in the segment descriptor.

Is the type field of struct kvm_segment the descriptor type?
If so, why type is checked when setting segment registers?

If the type field is not the descriptor type,
is it ok to set unusable when present is 1?

I'm copying a code as following to show what code I'm asking.

----------------------------- 8< ---------------------------------
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5f48f62..0133f6f 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1803,7 +1803,7 @@ static void svm_get_segment(struct kvm_vcpu *vcpu,
 	 * AMD's VMCB does not have an explicit unusable field, so emulate it
 	 * for cross vendor migration purposes by "not present"
 	 */
-	var->unusable = !var->present || (var->type == 0);
+	var->unusable = !var->present;

 	switch (seg) {
 	case VCPU_SREG_TR:
-- 
2.5.0