linux-kernel - [PATCH 37/47] KVM: When switching to a vm8086 task, load segments as 16-bit

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

Message-Id: <1251282609-12835-38-git-send-email-avi@redhat.com>
Date:	Wed, 26 Aug 2009 13:29:59 +0300
From:	Avi Kivity <avi@...hat.com>
To:	kvm@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 37/47] KVM: When switching to a vm8086 task, load segments as 16-bit

From: Anthony Liguori <aliguori@...ibm.com>

According to 16.2.5 in the SDM, eflags.vm in the tss is consulted before loading
and new segments.  If eflags.vm == 1, then the segments are treated as 16-bit
segments.  The LDTR and TR are not normally available in vm86 mode so if they
happen to somehow get loaded, they need to be treated as 32-bit segments.

This fixes an invalid vmentry failure in a custom OS that was happening after
a task switch into vm8086 mode.  Since the segments were being mistakenly
treated as 32-bit, we loaded garbage state.

Signed-off-by: Anthony Liguori <aliguori@...ibm.com>
Signed-off-by: Avi Kivity <avi@...hat.com>
---
 arch/x86/kvm/x86.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 31bf984..1aa7e6d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4101,12 +4101,19 @@ static int kvm_load_realmode_segment(struct kvm_vcpu *vcpu, u16 selector, int se
 	return 0;
 }
 
+static int is_vm86_segment(struct kvm_vcpu *vcpu, int seg)
+{
+	return (seg != VCPU_SREG_LDTR) &&
+		(seg != VCPU_SREG_TR) &&
+		(kvm_x86_ops->get_rflags(vcpu) & X86_EFLAGS_VM);
+}
+
 int kvm_load_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
 				int type_bits, int seg)
 {
 	struct kvm_segment kvm_seg;
 
-	if (!(vcpu->arch.cr0 & X86_CR0_PE))
+	if (is_vm86_segment(vcpu, seg) || !(vcpu->arch.cr0 & X86_CR0_PE))
 		return kvm_load_realmode_segment(vcpu, selector, seg);
 	if (load_segment_descriptor_to_kvm_desct(vcpu, selector, &kvm_seg))
 		return 1;
-- 
1.6.4.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/