add APIs for detecting confidential virtualization

This code uses various CPUID checks to be able to identify

 * AMD SEV
 * AMD SEV-ES
 * AMD SEV-SNP
 * Intel TDX

On HyperV/Azure, it has special checks for detecting SEV-SNP
since the normal CPUID is blocked.

Related: https://github.com/systemd/systemd/issues/27604
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/basic/confidential-virt.c

@@ -0,0 +1,293 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#if defined(__i386__) || defined(__x86_64__)
+#include <cpuid.h>
+#endif
+#include <errno.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "confidential-virt.h"
+#include "fd-util.h"
+#include "missing_threads.h"
+#include "string-table.h"
+#include "utf8.h"
+
+#define CPUID_PROCESSOR_INFO_AND_FEATURE_BITS UINT32_C(0x1)
+
+/*
+ * AMD64 Architecture Programmer’s Manual Volume 3:
+ * General-Purpose and System Instructions.
+ * Chapter: E4.1 - Maximum Extended Function Number and Vendor String
+ *  https://www.amd.com/system/files/TechDocs/24594.pdf
+ */
+#define CPUID_GET_HIGHEST_FUNCTION UINT32_C(0x80000000)
+
+/*
+ * AMD64 Architecture Programmer’s Manual Volume 3:
+ * General-Purpose and System Instructions.
+ * Chapter: E4.17 - Encrypted Memory Capabilities
+ *  https://www.amd.com/system/files/TechDocs/24594.pdf
+ */
+#define CPUID_AMD_GET_ENCRYPTED_MEMORY_CAPABILITIES UINT32_C(0x8000001f)
+
+/*
+ * AMD64 Architecture Programmer’s Manual Volume 3:
+ * General-Purpose and System Instructions.
+ * Chapter: 15.34.10 - SEV_STATUS MSR
+ * https://www.amd.com/system/files/TechDocs/24593.pdf
+ */
+#define MSR_AMD64_SEV UINT32_C(0xc0010131)
+
+/*
+ * Intel® TDX Module v1.5 Base Architecture Specification
+ * Chapter: 11.2
+ * https://www.intel.com/content/www/us/en/content-details/733575/intel-tdx-module-v1-5-base-architecture-specification.html
+ */
+
+#define CPUID_INTEL_TDX_ENUMERATION UINT32_C(0x21)
+
+/* Requirements for Implementing the Microsoft Hypervisor Interface
+ * https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/tlfs
+ */
+#define CPUID_HYPERV_VENDOR_AND_MAX_FUNCTIONS UINT32_C(0x40000000)
+
+#define CPUID_HYPERV_FEATURES UINT32_C(0x40000003)
+
+#define CPUID_HYPERV_ISOLATION_CONFIG UINT32_C(0x4000000C)
+
+#define CPUID_HYPERV_MIN UINT32_C(0x40000005)
+#define CPUID_HYPERV_MAX UINT32_C(0x4000ffff)
+
+#define CPUID_SIG_AMD       "AuthenticAMD"
+#define CPUID_SIG_INTEL     "GenuineIntel"
+#define CPUID_SIG_INTEL_TDX "IntelTDX    "
+#define CPUID_SIG_HYPERV    "Microsoft Hv"
+
+/* ecx bit 31: set => hyperpvisor, unset => bare metal */
+#define CPUID_FEATURE_HYPERVISOR (UINT32_C(1) << 31)
+
+/* Linux include/asm-generic/hyperv-tlfs.h */
+#define CPUID_HYPERV_CPU_MANAGEMENT (UINT32_C(1) << 12) /* root partition */
+#define CPUID_HYPERV_ISOLATION      (UINT32_C(1) << 22) /* confidential VM partition */
+
+#define CPUID_HYPERV_ISOLATION_TYPE_MASK UINT32_C(0xf)
+#define CPUID_HYPERV_ISOLATION_TYPE_SNP 2
+
+#define EAX_SEV     (UINT32_C(1) << 1)
+#define MSR_SEV     (UINT64_C(1) << 0)
+#define MSR_SEV_ES  (UINT64_C(1) << 1)
+#define MSR_SEV_SNP (UINT64_C(1) << 2)
+
+#if defined(__x86_64__)
+
+static void cpuid(uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx) {
+        log_debug("CPUID func %" PRIx32 " %" PRIx32, *eax, *ecx);
+        __cpuid_count(*eax, *ecx, *eax, *ebx, *ecx, *edx);
+        log_debug("CPUID result %" PRIx32 " %" PRIx32 " %" PRIx32 " %" PRIx32, *eax, *ebx, *ecx, *edx);
+}
+
+static uint32_t cpuid_leaf(uint32_t eax, char ret_sig[static 13], bool swapped) {
+        /* zero-init as some queries explicitly require subleaf == 0 */
+        uint32_t sig[3] = {};
+
+        if (swapped)
+                cpuid(&eax, &sig[0], &sig[2], &sig[1]);
+        else
+                cpuid(&eax, &sig[0], &sig[1], &sig[2]);
+        memcpy(ret_sig, sig, sizeof(sig));
+        ret_sig[12] = 0; /* \0-terminate the string to make string comparison possible */
+
+        /* In some CI tests ret_sig doesn't contain valid UTF8 and prints garbage to the console */
+        log_debug("CPUID sig '%s'", strna(utf8_is_valid(ret_sig)));
+
+        return eax;
+}
+
+#define MSR_DEVICE "/dev/cpu/0/msr"
+
+static uint64_t msr(uint64_t index) {
+        uint64_t ret;
+        ssize_t rv;
+        _cleanup_close_ int fd = -EBADF;
+
+        fd = open(MSR_DEVICE, O_RDONLY|O_CLOEXEC);
+        if (fd < 0) {
+                log_debug_errno(errno,
+                                "Cannot open MSR device %s (index %" PRIu64 "), ignoring: %m",
+                                MSR_DEVICE,
+                                index);
+                return 0;
+        }
+
+        rv = pread(fd, &ret, sizeof(ret), index);
+        if (rv < 0) {
+                log_debug_errno(errno,
+                                "Cannot read MSR device %s (index %" PRIu64 "), ignoring: %m",
+                                MSR_DEVICE,
+                                index);
+                return 0;
+        } else if (rv != sizeof(ret)) {
+                log_debug("Short read %ld bytes from MSR device %s (index %" PRIu64 "), ignoring",
+                          rv,
+                          MSR_DEVICE,
+                          index);
+                return 0;
+        }
+
+        log_debug("MSR %" PRIu64 " result %" PRIu64 "", index, ret);
+        return ret;
+}
+
+static bool detect_hyperv_sev(void) {
+        uint32_t eax, ebx, ecx, edx, feat;
+        char sig[13] = {};
+
+        feat = cpuid_leaf(CPUID_HYPERV_VENDOR_AND_MAX_FUNCTIONS, sig, false);
+
+        if (feat < CPUID_HYPERV_MIN || feat > CPUID_HYPERV_MAX)
+                return false;
+
+        if (memcmp(sig, CPUID_SIG_HYPERV, sizeof(sig)) != 0)
+                return false;
+
+        log_debug("CPUID is on hyperv");
+        eax = CPUID_HYPERV_FEATURES;
+        ebx = ecx = edx = 0;
+
+        cpuid(&eax, &ebx, &ecx, &edx);
+
+        if (ebx & CPUID_HYPERV_ISOLATION && !(ebx & CPUID_HYPERV_CPU_MANAGEMENT)) {
+
+                eax = CPUID_HYPERV_ISOLATION_CONFIG;
+                ebx = ecx = edx = 0;
+                cpuid(&eax, &ebx, &ecx, &edx);
+
+                if ((ebx & CPUID_HYPERV_ISOLATION_TYPE_MASK) == CPUID_HYPERV_ISOLATION_TYPE_SNP)
+                        return true;
+        }
+
+        return false;
+}
+
+static ConfidentialVirtualization detect_sev(void) {
+        uint32_t eax, ebx, ecx, edx;
+        uint64_t msrval;
+
+        eax = CPUID_GET_HIGHEST_FUNCTION;
+        ebx = ecx = edx = 0;
+
+        cpuid(&eax, &ebx, &ecx, &edx);
+
+        if (eax < CPUID_AMD_GET_ENCRYPTED_MEMORY_CAPABILITIES)
+                return CONFIDENTIAL_VIRTUALIZATION_NONE;
+
+        eax = CPUID_AMD_GET_ENCRYPTED_MEMORY_CAPABILITIES;
+        ebx = ecx = edx = 0;
+
+        cpuid(&eax, &ebx, &ecx, &edx);
+
+        /* bit 1 == CPU supports SEV feature
+         *
+         * Note, Azure blocks this CPUID leaf from its SEV-SNP
+         * guests, so we must fallback to trying some HyperV
+         * specific CPUID checks.
+         */
+        if (!(eax & EAX_SEV)) {
+                log_debug("No sev in CPUID, trying hyperv CPUID");
+
+                if (detect_hyperv_sev())
+                        return CONFIDENTIAL_VIRTUALIZATION_SEV_SNP;
+
+                log_debug("No hyperv CPUID");
+                return CONFIDENTIAL_VIRTUALIZATION_NONE;
+        }
+
+        msrval = msr(MSR_AMD64_SEV);
+
+        /* Test reverse order, since the SEV-SNP bit implies
+         * the SEV-ES bit, which implies the SEV bit */
+        if (msrval & MSR_SEV_SNP)
+                return CONFIDENTIAL_VIRTUALIZATION_SEV_SNP;
+        if (msrval & MSR_SEV_ES)
+                return CONFIDENTIAL_VIRTUALIZATION_SEV_ES;
+        if (msrval & MSR_SEV)
+                return CONFIDENTIAL_VIRTUALIZATION_SEV;
+
+        return CONFIDENTIAL_VIRTUALIZATION_NONE;
+}
+
+static ConfidentialVirtualization detect_tdx(void) {
+        uint32_t eax, ebx, ecx, edx;
+        char sig[13] = {};
+
+        eax = CPUID_GET_HIGHEST_FUNCTION;
+        ebx = ecx = edx = 0;
+
+        cpuid(&eax, &ebx, &ecx, &edx);
+
+        if (eax < CPUID_INTEL_TDX_ENUMERATION)
+                return CONFIDENTIAL_VIRTUALIZATION_NONE;
+
+        cpuid_leaf(CPUID_INTEL_TDX_ENUMERATION, sig, true);
+
+        if (memcmp(sig, CPUID_SIG_INTEL_TDX, sizeof(sig)) == 0)
+                return CONFIDENTIAL_VIRTUALIZATION_TDX;
+
+        return CONFIDENTIAL_VIRTUALIZATION_NONE;
+}
+
+static bool detect_hypervisor(void) {
+        uint32_t eax, ebx, ecx, edx;
+        bool is_hv;
+
+        eax = CPUID_PROCESSOR_INFO_AND_FEATURE_BITS;
+        ebx = ecx = edx = 0;
+
+        cpuid(&eax, &ebx, &ecx, &edx);
+
+        is_hv = ecx & CPUID_FEATURE_HYPERVISOR;
+
+        log_debug("CPUID is hypervisor: %s", yes_no(is_hv));
+        return is_hv;
+}
+
+ConfidentialVirtualization detect_confidential_virtualization(void) {
+        static thread_local ConfidentialVirtualization cached_found = _CONFIDENTIAL_VIRTUALIZATION_INVALID;
+        char sig[13] = {};
+        ConfidentialVirtualization cv = CONFIDENTIAL_VIRTUALIZATION_NONE;
+
+        if (cached_found >= 0)
+                return cached_found;
+
+        /* Skip everything on bare metal */
+        if (detect_hypervisor()) {
+                cpuid_leaf(0, sig, true);
+
+                if (memcmp(sig, CPUID_SIG_AMD, sizeof(sig)) == 0)
+                        cv = detect_sev();
+                else if (memcmp(sig, CPUID_SIG_INTEL, sizeof(sig)) == 0)
+                        cv = detect_tdx();
+        }
+
+        cached_found = cv;
+        return cv;
+}
+#else /* ! x86_64 */
+ConfidentialVirtualization detect_confidential_virtualization(void) {
+        log_debug("No confidential virtualization detection on this architecture");
+        return CONFIDENTIAL_VIRTUALIZATION_NONE;
+}
+#endif /* ! x86_64 */
+
+static const char *const confidential_virtualization_table[_CONFIDENTIAL_VIRTUALIZATION_MAX] = {
+        [CONFIDENTIAL_VIRTUALIZATION_NONE]    = "none",
+        [CONFIDENTIAL_VIRTUALIZATION_SEV]     = "sev",
+        [CONFIDENTIAL_VIRTUALIZATION_SEV_ES]  = "sev-es",
+        [CONFIDENTIAL_VIRTUALIZATION_SEV_SNP] = "sev-snp",
+        [CONFIDENTIAL_VIRTUALIZATION_TDX]     = "tdx",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(confidential_virtualization, ConfidentialVirtualization);

src/basic/confidential-virt.h

@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <stdbool.h>
+
+#include "errno-list.h"
+#include "macro.h"
+
+typedef enum ConfidentialVirtualization {
+        CONFIDENTIAL_VIRTUALIZATION_NONE = 0,
+
+        CONFIDENTIAL_VIRTUALIZATION_SEV,
+        CONFIDENTIAL_VIRTUALIZATION_SEV_ES,
+        CONFIDENTIAL_VIRTUALIZATION_SEV_SNP,
+        CONFIDENTIAL_VIRTUALIZATION_TDX,
+
+        _CONFIDENTIAL_VIRTUALIZATION_MAX,
+        _CONFIDENTIAL_VIRTUALIZATION_INVALID = -EINVAL,
+        _CONFIDENTIAL_VIRTUALIZATION_ERRNO_MAX = -ERRNO_MAX, /* ensure full range of errno fits into this enum */
+} ConfidentialVirtualization;
+
+ConfidentialVirtualization detect_confidential_virtualization(void);
+
+const char *confidential_virtualization_to_string(ConfidentialVirtualization v) _const_;
+ConfidentialVirtualization confidential_virtualization_from_string(const char *s) _pure_;

src/basic/meson.build

@@ -16,6 +16,7 @@ basic_sources = files(
         'chase.c',
         'chattr-util.c',
         'conf-files.c',
+        'confidential-virt.c',
         'devnum-util.c',
         'dirent-util.c',
         'efivars.c',

src/test/test-tables.c

@@ -6,6 +6,7 @@
 #include "cgroup-util.h"
 #include "compress.h"
 #include "condition.h"
+#include "confidential-virt.h"
 #include "device-private.h"
 #include "device.h"
 #include "discover-image.h"
@@ -49,6 +50,7 @@ int main(int argc, char **argv) {
         test_table(collect_mode, COLLECT_MODE);
         test_table(condition_result, CONDITION_RESULT);
         test_table(condition_type, CONDITION_TYPE);
+        test_table(confidential_virtualization, CONFIDENTIAL_VIRTUALIZATION);
         test_table(device_action, SD_DEVICE_ACTION);
         test_table(device_state, DEVICE_STATE);
         test_table(dns_over_tls_mode, DNS_OVER_TLS_MODE);