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    Subject[PATCH 5.10 529/545] KVM: x86: Check lapic_in_kernel() before attempting to set a SynIC irq
    Date
    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: Stefan Ghinea <stefan.ghinea@windriver.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
    @@ -428,6 +428,9 @@ 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;


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