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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Vitaly Kuznetsov <vkuznets@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH 4.14 202/284] KVM: x86: Forbid VMM to set SYNIC/STIMER MSRs when SynIC wasnt activated
Date:   Mon, 18 Apr 2022 14:13:03 +0200
Message-Id: <20220418121217.469428260@linuxfoundation.org>
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From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit b1e34d325397a33d97d845e312d7cf2a8b646b44 upstream.

Setting non-zero values to SYNIC/STIMER MSRs activates certain features,
this should not happen when KVM_CAP_HYPERV_SYNIC{,2} was not activated.

Note, it would've been better to forbid writing anything to SYNIC/STIMER
MSRs, including zeroes, however, at least QEMU tries clearing
HV_X64_MSR_STIMER0_CONFIG without SynIC. HV_X64_MSR_EOM MSR is somewhat
'special' as writing zero there triggers an action, this also should not
happen when SynIC wasn't activated.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220325132140.25650-4-vkuznets@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kvm/hyperv.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -260,6 +260,9 @@ static int synic_set_msr(struct kvm_vcpu
 	case HV_X64_MSR_EOM: {
 		int i;
 
+		if (!synic->active)
+			break;
+
 		for (i = 0; i < ARRAY_SIZE(synic->sint); i++)
 			kvm_hv_notify_acked_sint(vcpu, i);
 		break;
@@ -520,6 +523,12 @@ static int stimer_start(struct kvm_vcpu_
 static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config,
 			     bool host)
 {
+	struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer);
+	struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
+
+	if (!synic->active && (!host || config))
+		return 1;
+
 	trace_kvm_hv_stimer_set_config(stimer_to_vcpu(stimer)->vcpu_id,
 				       stimer->index, config, host);
 
@@ -534,6 +543,12 @@ static int stimer_set_config(struct kvm_
 static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count,
 			    bool host)
 {
+	struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer);
+	struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
+
+	if (!synic->active && (!host || count))
+		return 1;
+
 	trace_kvm_hv_stimer_set_count(stimer_to_vcpu(stimer)->vcpu_id,
 				      stimer->index, count, host);