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    Subject[PATCH v6 14/33] KVM: nVMX: WARN once and fail VM-Enter if eVMCS sees VMFUNC[63:32] != 0
    Date
    From: Sean Christopherson <seanjc@google.com>

    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>
    Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.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 c3a5309f6e82..b64e29f1359f 100644
    --- a/arch/x86/kvm/vmx/evmcs.c
    +++ b/arch/x86/kvm/vmx/evmcs.c
    @@ -469,6 +469,14 @@ int nested_evmcs_check_controls(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(EVMCS_VMFUNC,
    vmcs12->vm_function_control)))
    return -EINVAL;
    --
    2.37.2
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