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KVM: x86/xen: Only do in-kernel acceleration of hypercalls for guest CPL0

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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>
This commit is contained in:
David Woodhouse 2022-11-12 13:52:25 +00:00 committed by Paolo Bonzini
parent 4ea9439fd5
commit c2b8cdfaf3
1 changed files with 11 additions and 1 deletions
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12
arch/x86/kvm/xen.c
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@ -1227,6 +1227,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
bool longmode;
u64 input, params[6], r = -ENOSYS;
bool handled = false;
u8 cpl;
input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX);
@ -1254,9 +1255,17 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
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) {
@ -1291,10 +1300,11 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
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];