KVM: x86: Reject fixeds-size Hyper-V hypercalls with non-zero "var_cnt"
Reject Hyper-V hypercalls if the guest specifies a non-zero variable size
header (var_cnt in KVM) for a hypercall that has a fixed header size.
Per the TLFS:
It is illegal to specify a non-zero variable header size for a
hypercall that is not explicitly documented as accepting variable sized
input headers. In such a case the hypercall will result in a return
code of HV_STATUS_INVALID_HYPERCALL_INPUT.
Note, at least some of the various DEBUG commands likely aren't allowed
to use variable size headers, but the TLFS documentation doesn't clearly
state what is/isn't allowed. Omit them for now to avoid unnecessary
breakage.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <
20211207220926.718794-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>