[PATCH 24/30] KVM: x86: hyper-v: Honor HV_DEBUGGING privilege bit

[Vitaly Kuznetsov]

Hyper-V partition must possess 'HV_DEBUGGING' privilege to issue
HVCALL_POST_DEBUG_DATA/HVCALL_RETRIEVE_DEBUG_DATA/
HVCALL_RESET_DEBUG_SESSION hypercalls.

Note, when SynDBG is disabled hv_check_hypercall_access() returns
'true' (like for any other unknown hypercall) so the result will
be HV_STATUS_INVALID_HYPERCALL_CODE and not HV_STATUS_ACCESS_DENIED.

Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
 arch/x86/kvm/hyperv.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 523f63287636..36ec688cda4e 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2035,6 +2035,15 @@ static bool hv_check_hypercall_access(struct kvm_vcpu_hv 
*hv_vcpu, u16 code)
                return hv_vcpu->cpuid_cache.features_ebx & HV_POST_MESSAGES;
        case HVCALL_SIGNAL_EVENT:
                return hv_vcpu->cpuid_cache.features_ebx & HV_SIGNAL_EVENTS;
+       case HVCALL_POST_DEBUG_DATA:
+       case HVCALL_RETRIEVE_DEBUG_DATA:
+       case HVCALL_RESET_DEBUG_SESSION:
+               /*
+                * Return 'true' when SynDBG is disabled so the resulting code
+                * will be HV_STATUS_INVALID_HYPERCALL_CODE.
+                */
+               return !kvm_hv_is_syndbg_enabled(hv_vcpu->vcpu) ||
+                       hv_vcpu->cpuid_cache.features_ebx & HV_DEBUGGING;
        default:
                break;
        }
-- 
2.30.2