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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 5.15 810/913] KVM: x86: Check lapic_in_kernel() before attempting to set a SynIC irq
Date:   Tue,  5 Apr 2022 09:31:12 +0200
Message-Id: <20220405070404.112004907@linuxfoundation.org>
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From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit 7ec37d1cbe17d8189d9562178d8b29167fe1c31a upstream.

When KVM_CAP_HYPERV_SYNIC{,2} is activated, KVM already checks for
irqchip_in_kernel() so normally SynIC irqs should never be set. It is,
however,  possible for a misbehaving VMM to write to SYNIC/STIMER MSRs
causing erroneous behavior.

The immediate issue being fixed is that kvm_irq_delivery_to_apic()
(kvm_irq_delivery_to_apic_fast()) crashes when called with
'irq.shorthand = APIC_DEST_SELF' and 'src == NULL'.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220325132140.25650-2-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 |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -446,6 +446,9 @@ static int synic_set_irq(struct kvm_vcpu
 	struct kvm_lapic_irq irq;
 	int ret, vector;
 
+	if (KVM_BUG_ON(!lapic_in_kernel(vcpu), vcpu->kvm))
+		return -EINVAL;
+
 	if (sint >= ARRAY_SIZE(synic->sint))
 		return -EINVAL;