[RFC PATCH v6 15/36] KVM: nVMX: WARN once and fail VM-Enter if eVMCS sees VMFUNC[63:32] != 0

Sean Christopherson
2022-08-24T03:04:12Z

WARN and reject nested VM-Enter if KVM is using eVMCS and manages to
allow a non-zero value in the upper 32 bits of VM-function controls. The
eVMCS code assumes all inputs are 32-bit values and subtly drops the
upper bits. WARN instead of adding proper "support", it's unlikely the
upper bits will be defined/used in the next decade.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/evmcs.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index ce358b13b75b..bd1dcc077c85 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -486,6 +486,14 @@ int nested_evmcs_check_controls(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
vmcs12->vm_entry_controls)))
return -EINVAL;

+ /*
+ * VM-Func controls are 64-bit, but KVM currently doesn't support any
+ * controls in bits 63:32, i.e. dropping those bits on the consistency
+ * check is intentional.
+ */
+ if (WARN_ON_ONCE(vmcs12->vm_function_control >> 32))
+ return -EINVAL;
+
if (CC(!nested_evmcs_is_valid_controls(vcpu, EVMCS_VMFUNC,
vmcs12->vm_function_control)))
return -EINVAL;
--
2.37.1.595.g718a3a8f04-goog