The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7ec37d1cbe17d8189d9562178d8b29167fe1c31a Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov vkuznets@redhat.com Date: Fri, 25 Mar 2022 14:21:38 +0100 Subject: [PATCH] KVM: x86: Check lapic_in_kernel() before attempting to set a SynIC irq

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

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index a32f54ab84a2..f715b5a2b0e4 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -449,6 +449,9 @@ static int synic_set_irq(struct kvm_vcpu_hv_synic *synic, u32 sint) 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;