From: David Woodhouse <dwmw@xxxxxxxxxxxx>
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@xxxxxxx>
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
arch/x86/kvm/xen.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index dc2f304f2e69..f3098c0e386a 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -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];
--
2.35.3
