[pve-devel] [PATCH qemu-server v2 2/3] Add check for TDX support

[Anton Iacobaeus]

From: Philipp Giersfeld <philipp.giersfeld at canarybit.eu>

Check whether TDX is enabled on this machine. Instead of using CPUID
like AMD SEV, Intel TDX enablement can be verified by reading an MSR
(https://cc-enabling.trustedservices.intel.com/intel-tdx-enabling-guide/05/host_os_setup/).

Signed-off-by: Philipp Giersfeld <philipp.giersfeld at canarybit.eu>
Signed-off-by: Anton Iacobaeus <anton.iacobaeus at canarybit.eu>
---
 .../query-machine-capabilities.c              | 97 ++++++++++++++++---
 src/usr/modules-load.conf                     |  1 +
 2 files changed, 85 insertions(+), 13 deletions(-)

diff --git a/src/query-machine-capabilities/query-machine-capabilities.c b/src/query-machine-capabilities/query-machine-capabilities.c
index 0c522afc..5bc39450 100644
--- a/src/query-machine-capabilities/query-machine-capabilities.c
+++ b/src/query-machine-capabilities/query-machine-capabilities.c
@@ -4,6 +4,8 @@
 #include <sys/stat.h>
 #include <errno.h>
 #include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
 
 #define eprintf(...) fprintf(stderr, __VA_ARGS__)
 
@@ -18,17 +20,56 @@ typedef struct {
 
     uint8_t cbitpos;
     uint8_t reduced_phys_bits;
-} cpu_caps_t;
+} cpu_caps_amd_sev_t;
 
-void query_cpu_capabilities(cpu_caps_t *res) {
+typedef struct {
+    bool tdx_support;
+} cpu_caps_intel_tdx_t;
+
+int read_msr(uint32_t msr_index, unsigned int *value) {
+    int64_t data;
+    char* msr_file_name = "/dev/cpu/0/msr";
+    int fd;
+
+    fd = open(msr_file_name, O_RDONLY);
+    if (fd < 0) {
+        if (errno == ENXIO) {
+            eprintf("rdmsr: No CPU 0\n");
+            return -1;
+        } else if (errno == EIO) {
+            eprintf("rdmsr: CPU doesn't support MSRs\n");
+            return -1;
+        } else {
+            perror("rdmsr: failed to open MSR");
+            return -1;
+        }
+    }
+
+    if (pread(fd, &data, sizeof data, msr_index) != sizeof data) {
+        if (errno == EIO) {
+            eprintf("rdmsr: CPU cannot read MSR 0x%08x\n", msr_index);
+            return -1;
+        } else {
+            perror("rdmsr: pread");
+            return -1;
+        }
+    }
+
+    *value = data;
+
+    close(fd);
+    return 0;
+}
+
+void query_cpu_capabilities_sev(cpu_caps_amd_sev_t *res) {
     uint32_t eax, ebx, ecx, edx;
 
     // query Encrypted Memory Capabilities, see:
     // https://en.wikipedia.org/wiki/CPUID#EAX=8000001Fh:_Encrypted_Memory_Capabilities
     uint32_t query_function = 0x8000001F;
     asm volatile("cpuid"
-         : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx)
-         : "0"(query_function)
+        : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx)
+        : "0"(query_function)
     );
 
     res->sev_support = (eax & (1<<1)) != 0;
@@ -39,6 +80,18 @@ void query_cpu_capabilities(cpu_caps_t *res) {
     res->reduced_phys_bits = (ebx >> 6) & 0x3f;
 }
 
+int query_cpu_capabilities_tdx(cpu_caps_intel_tdx_t *res) {
+    unsigned int value;
+
+    if (read_msr(0x1401, &value) == 0) {
+        res->tdx_support = (value & (1<<11));
+    } else {
+        eprintf("Error reading MSR, Intel TDX support undetermined\n");
+        return -1;
+    }
+    return 0;
+}
+
 int prepare_output_directory() {
     // Check that the directory exists and create it if it does not.
     struct stat statbuf;
@@ -65,8 +118,8 @@ int main() {
         return 1;
     }
 
-    cpu_caps_t caps;
-    query_cpu_capabilities(&caps);
+    cpu_caps_amd_sev_t caps_sev;
+    query_cpu_capabilities_sev(&caps_sev);
 
     FILE *file = fopen(OUTPUT_PATH, "w");
     if (file == NULL) {
@@ -82,18 +135,36 @@ int main() {
         " \"sev-support\": %s,"
         " \"sev-support-es\": %s,"
         " \"sev-support-snp\": %s"
-        " }"
-        " }\n",
-        caps.cbitpos,
-        caps.reduced_phys_bits,
-        caps.sev_support ? "true" : "false",
-        caps.sev_es_support ? "true" : "false",
-        caps.sev_snp_support ? "true" : "false"
+        " }",
+        caps_sev.cbitpos,
+        caps_sev.reduced_phys_bits,
+        caps_sev.sev_support ? "true" : "false",
+        caps_sev.sev_es_support ? "true" : "false",
+        caps_sev.sev_snp_support ? "true" : "false"
     );
     if (ret < 0) {
         eprintf("Error writing to file '" OUTPUT_PATH "': %s\n", strerror(errno));
     }
 
+    cpu_caps_intel_tdx_t caps_tdx;
+    if (query_cpu_capabilities_tdx(&caps_tdx) == 0) {
+        ret = fprintf(file,
+            ","
+            " \"intel-tdx\": {"
+            " \"tdx-support\": %s"
+            " }",
+            caps_tdx.tdx_support ? "true" : "false"
+        );
+        if (ret < 0) {
+            eprintf("Error writing to file '" OUTPUT_PATH "': %s\n", strerror(errno));
+        }
+    }
+
+    ret = fprintf(file, " }\n");
+    if (ret < 0) {
+        eprintf("Error writing to file '" OUTPUT_PATH "': %s\n", strerror(errno));
+    }
+
     ret = fclose(file);
     if (ret != 0) {
         eprintf("Error closing file '" OUTPUT_PATH "': %s\n", strerror(errno));
diff --git a/src/usr/modules-load.conf b/src/usr/modules-load.conf
index aee7d42a..f45d256b 100644
--- a/src/usr/modules-load.conf
+++ b/src/usr/modules-load.conf
@@ -1 +1,2 @@
 vhost_net
+msr
-- 
2.43.0