From: David Woodhouse dwmw@amazon.co.uk
commit c2b8cdfaf3a6721afe0c8c060a631b1c67a7f1ee upstream.
There are almost no hypercalls which are valid from CPL > 0, and definitely none which are handled by the kernel.
Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests") Reported-by: Michal Luczaj mhal@rbox.co Signed-off-by: David Woodhouse dwmw@amazon.co.uk Reviewed-by: Sean Christopherson seanjc@google.com Cc: stable@kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/xen.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1216,6 +1216,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *v bool longmode; u64 input, params[6], r = -ENOSYS; bool handled = false; + u8 cpl;
input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX);
@@ -1243,9 +1244,17 @@ int kvm_xen_hypercall(struct kvm_vcpu *v params[5] = (u64)kvm_r9_read(vcpu); } #endif + cpl = static_call(kvm_x86_get_cpl)(vcpu); trace_kvm_xen_hypercall(input, params[0], params[1], params[2], params[3], params[4], params[5]);
+ /* + * Only allow hypercall acceleration for CPL0. The rare hypercalls that + * are permitted in guest userspace can be handled by the VMM. + */ + if (unlikely(cpl > 0)) + goto handle_in_userspace; + switch (input) { case __HYPERVISOR_xen_version: if (params[0] == XENVER_version && vcpu->kvm->arch.xen.xen_version) { @@ -1280,10 +1289,11 @@ int kvm_xen_hypercall(struct kvm_vcpu *v if (handled) return kvm_xen_hypercall_set_result(vcpu, r);
+handle_in_userspace: vcpu->run->exit_reason = KVM_EXIT_XEN; vcpu->run->xen.type = KVM_EXIT_XEN_HCALL; vcpu->run->xen.u.hcall.longmode = longmode; - vcpu->run->xen.u.hcall.cpl = static_call(kvm_x86_get_cpl)(vcpu); + vcpu->run->xen.u.hcall.cpl = cpl; vcpu->run->xen.u.hcall.input = input; vcpu->run->xen.u.hcall.params[0] = params[0]; vcpu->run->xen.u.hcall.params[1] = params[1];