Fix detection of TDX confidential VM on Azure platform

The original CVM detection logic for TDX assumes that the guest can see
the standard TDX CPUID leaf. This was true in Azure when this code was
originally written, however, current Azure now blocks that leaf in the
paravisor. Instead it is required to use the same Azure specific CPUID
leaf that is used for SEV-SNP detection, which reports the VM isolation
type.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit 9d7be044cad1ae54e344daf8f2ec37da46faf0fd)

Related: RHEL-50651

src/basic/confidential-virt.c

@@ -77,7 +77,7 @@ static uint64_t msr(uint64_t index) {
         return ret;
 }
 
-static bool detect_hyperv_sev(void) {
+static bool detect_hyperv_cvm(uint32_t isoltype) {
         uint32_t eax, ebx, ecx, edx, feat;
         char sig[13] = {};
 
@@ -101,7 +101,7 @@ static bool detect_hyperv_sev(void) {
                 ebx = ecx = edx = 0;
                 cpuid(&eax, &ebx, &ecx, &edx);
 
-                if ((ebx & CPUID_HYPERV_ISOLATION_TYPE_MASK) == CPUID_HYPERV_ISOLATION_TYPE_SNP)
+                if ((ebx & CPUID_HYPERV_ISOLATION_TYPE_MASK) == isoltype)
                         return true;
         }
 
@@ -134,7 +134,7 @@ static ConfidentialVirtualization detect_sev(void) {
         if (!(eax & EAX_SEV)) {
                 log_debug("No sev in CPUID, trying hyperv CPUID");
 
-                if (detect_hyperv_sev())
+                if (detect_hyperv_cvm(CPUID_HYPERV_ISOLATION_TYPE_SNP))
                         return CONFIDENTIAL_VIRTUALIZATION_SEV_SNP;
 
                 log_debug("No hyperv CPUID");
@@ -172,6 +172,11 @@ static ConfidentialVirtualization detect_tdx(void) {
         if (memcmp(sig, CPUID_SIG_INTEL_TDX, sizeof(sig)) == 0)
                 return CONFIDENTIAL_VIRTUALIZATION_TDX;
 
+        log_debug("No tdx in CPUID, trying hyperv CPUID");
+
+        if (detect_hyperv_cvm(CPUID_HYPERV_ISOLATION_TYPE_TDX))
+                return CONFIDENTIAL_VIRTUALIZATION_TDX;
+
         return CONFIDENTIAL_VIRTUALIZATION_NONE;
 }
 

src/boot/efi/vmm.c

@@ -353,7 +353,7 @@ static uint64_t msr(uint32_t index) {
         return val;
 }
 
-static bool detect_hyperv_sev(void) {
+static bool detect_hyperv_cvm(uint32_t isoltype) {
         uint32_t eax, ebx, ecx, edx, feat;
         char sig[13] = {};
 
@@ -370,7 +370,7 @@ static bool detect_hyperv_sev(void) {
         if (ebx & CPUID_HYPERV_ISOLATION && !(ebx & CPUID_HYPERV_CPU_MANAGEMENT)) {
                 __cpuid(CPUID_HYPERV_ISOLATION_CONFIG, eax, ebx, ecx, edx);
 
-                if ((ebx & CPUID_HYPERV_ISOLATION_TYPE_MASK) == CPUID_HYPERV_ISOLATION_TYPE_SNP)
+                if ((ebx & CPUID_HYPERV_ISOLATION_TYPE_MASK) == isoltype)
                         return true;
         }
 
@@ -395,7 +395,7 @@ static bool detect_sev(void) {
          * specific CPUID checks.
          */
         if (!(eax & EAX_SEV))
-                return detect_hyperv_sev();
+                return detect_hyperv_cvm(CPUID_HYPERV_ISOLATION_TYPE_SNP);
 
         msrval = msr(MSR_AMD64_SEV);
 
@@ -419,6 +419,9 @@ static bool detect_tdx(void) {
         if (memcmp(sig, CPUID_SIG_INTEL_TDX, sizeof(sig)) == 0)
                 return true;
 
+        if (detect_hyperv_cvm(CPUID_HYPERV_ISOLATION_TYPE_TDX))
+                return true;
+
         return false;
 }
 #endif /* ! __i386__ && ! __x86_64__ */

src/fundamental/confidential-virt-fundamental.h

@@ -65,6 +65,7 @@
 
 #define CPUID_HYPERV_ISOLATION_TYPE_MASK UINT32_C(0xf)
 #define CPUID_HYPERV_ISOLATION_TYPE_SNP 2
+#define CPUID_HYPERV_ISOLATION_TYPE_TDX 3
 
 #define EAX_SEV     (UINT32_C(1) << 1)
 #define MSR_SEV     (UINT64_C(1) << 0)