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[F/I,OEM-5.14,SRU] KVM: nVMX: Set LDTR to its architecturally defined value on nested VM-Exit

Message ID 20220406043621.20212-2-po-hsu.lin@canonical.com
State New
Headers show
Series [Bionic,SRU,1/1] KVM: nVMX: Set LDTR to its architecturally defined value on nested VM-Exit | expand

Commit Message

Po-Hsu Lin April 6, 2022, 4:36 a.m. UTC 
From: Sean Christopherson <seanjc@google.com>

BugLink: https://bugs.launchpad.net/bugs/1956315

Set L1's LDTR on VM-Exit per the Intel SDM:

  The host-state area does not contain a selector field for LDTR. LDTR is
  established as follows on all VM exits: the selector is cleared to
  0000H, the segment is marked unusable and is otherwise undefined
  (although the base address is always canonical).

This is likely a benign bug since the LDTR is unusable, as it means the
L1 VMM is conditioned to reload its LDTR in order to function properly on
bare metal.

Fixes: 4704d0befb07 ("KVM: nVMX: Exiting from L2 to L1")
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit afc8de0118be84f4058b9977d481aeb3e0758dbb)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
---
 arch/x86/kvm/vmx/nested.c | 4 ++++
 1 file changed, 4 insertions(+)
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Patch

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 3041015..857e275 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3926,6 +3926,10 @@  static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 	};
 	vmx_set_segment(vcpu, &seg, VCPU_SREG_TR);
 
+	memset(&seg, 0, sizeof(seg));
+	seg.unusable = 1;
+	vmx_set_segment(vcpu, &seg, VCPU_SREG_LDTR);
+
 	kvm_set_dr(vcpu, 7, 0x400);
 	vmcs_write64(GUEST_IA32_DEBUGCTL, 0);