i386/sev: Add support for SNP CPUID validation

SEV-SNP firmware allows a special guest page to be populated with a
table of guest CPUID values so that they can be validated through
firmware before being loaded into encrypted guest memory where they can
be used in place of hypervisor-provided values[1].

As part of SEV-SNP guest initialization, use this interface to validate
the CPUID entries reported by KVM_GET_CPUID2 prior to initial guest
start and populate the CPUID page reserved by OVMF with the resulting
encrypted data.

[1] SEV SNP Firmware ABI Specification, Rev. 0.8, 8.13.2.6

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
Message-ID: <20240530111643.1091816-21-pankaj.gupta@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/sev.c

@@ -200,6 +200,36 @@ static const char *const sev_fw_errlist[] = {
 
 #define SEV_FW_MAX_ERROR      ARRAY_SIZE(sev_fw_errlist)
 
+/* <linux/kvm.h> doesn't expose this, so re-use the max from kvm.c */
+#define KVM_MAX_CPUID_ENTRIES 100
+
+typedef struct KvmCpuidInfo {
+    struct kvm_cpuid2 cpuid;
+    struct kvm_cpuid_entry2 entries[KVM_MAX_CPUID_ENTRIES];
+} KvmCpuidInfo;
+
+#define SNP_CPUID_FUNCTION_MAXCOUNT 64
+#define SNP_CPUID_FUNCTION_UNKNOWN 0xFFFFFFFF
+
+typedef struct {
+    uint32_t eax_in;
+    uint32_t ecx_in;
+    uint64_t xcr0_in;
+    uint64_t xss_in;
+    uint32_t eax;
+    uint32_t ebx;
+    uint32_t ecx;
+    uint32_t edx;
+    uint64_t reserved;
+} __attribute__((packed)) SnpCpuidFunc;
+
+typedef struct {
+    uint32_t count;
+    uint32_t reserved1;
+    uint64_t reserved2;
+    SnpCpuidFunc entries[SNP_CPUID_FUNCTION_MAXCOUNT];
+} __attribute__((packed)) SnpCpuidInfo;
+
 static int
 sev_ioctl(int fd, int cmd, void *data, int *error)
 {
@@ -788,6 +818,35 @@ out:
     return ret;
 }
 
+static void
+sev_snp_cpuid_report_mismatches(SnpCpuidInfo *old,
+                                SnpCpuidInfo *new)
+{
+    size_t i;
+
+    if (old->count != new->count) {
+        error_report("SEV-SNP: CPUID validation failed due to count mismatch,"
+                     "provided: %d, expected: %d", old->count, new->count);
+        return;
+    }
+
+    for (i = 0; i < old->count; i++) {
+        SnpCpuidFunc *old_func, *new_func;
+
+        old_func = &old->entries[i];
+        new_func = &new->entries[i];
+
+        if (memcmp(old_func, new_func, sizeof(SnpCpuidFunc))) {
+            error_report("SEV-SNP: CPUID validation failed for function 0x%x, index: 0x%x"
+                         "provided: eax:0x%08x, ebx: 0x%08x, ecx: 0x%08x, edx: 0x%08x"
+                         "expected: eax:0x%08x, ebx: 0x%08x, ecx: 0x%08x, edx: 0x%08x",
+                         old_func->eax_in, old_func->ecx_in,
+                         old_func->eax, old_func->ebx, old_func->ecx, old_func->edx,
+                         new_func->eax, new_func->ebx, new_func->ecx, new_func->edx);
+        }
+    }
+}
+
 static const char *
 snp_page_type_to_str(int type)
 {
@@ -806,6 +865,7 @@ sev_snp_launch_update(SevSnpGuestState *sev_snp_guest,
                       SevLaunchUpdateData *data)
 {
     int ret, fw_error;
+    SnpCpuidInfo snp_cpuid_info;
     struct kvm_sev_snp_launch_update update = {0};
 
     if (!data->hva || !data->len) {
@@ -815,6 +875,11 @@ sev_snp_launch_update(SevSnpGuestState *sev_snp_guest,
         return 1;
     }
 
+    if (data->type == KVM_SEV_SNP_PAGE_TYPE_CPUID) {
+        /* Save a copy for comparison in case the LAUNCH_UPDATE fails */
+        memcpy(&snp_cpuid_info, data->hva, sizeof(snp_cpuid_info));
+    }
+
     update.uaddr = (__u64)(unsigned long)data->hva;
     update.gfn_start = data->gpa >> TARGET_PAGE_BITS;
     update.len = data->len;
@@ -842,6 +907,11 @@ sev_snp_launch_update(SevSnpGuestState *sev_snp_guest,
         if (ret && ret != -EAGAIN) {
             error_report("SNP_LAUNCH_UPDATE ret=%d fw_error=%d '%s'",
                          ret, fw_error, fw_error_to_str(fw_error));
+
+            if (data->type == KVM_SEV_SNP_PAGE_TYPE_CPUID) {
+                sev_snp_cpuid_report_mismatches(&snp_cpuid_info, data->hva);
+                error_report("SEV-SNP: failed update CPUID page");
+            }
             break;
         }
     }
@@ -1004,7 +1074,8 @@ sev_launch_finish(SevCommonState *sev_common)
 }
 
 static int
-snp_launch_update_data(uint64_t gpa, void *hva, uint32_t len, int type)
+snp_launch_update_data(uint64_t gpa, void *hva,
+                       uint32_t len, int type)
 {
     SevLaunchUpdateData *data;
 
@@ -1019,6 +1090,90 @@ snp_launch_update_data(uint64_t gpa, void *hva, uint32_t len, int type)
     return 0;
 }
 
+static int
+sev_snp_cpuid_info_fill(SnpCpuidInfo *snp_cpuid_info,
+                        const KvmCpuidInfo *kvm_cpuid_info)
+{
+    size_t i;
+
+    if (kvm_cpuid_info->cpuid.nent > SNP_CPUID_FUNCTION_MAXCOUNT) {
+        error_report("SEV-SNP: CPUID entry count (%d) exceeds max (%d)",
+                     kvm_cpuid_info->cpuid.nent, SNP_CPUID_FUNCTION_MAXCOUNT);
+        return -1;
+    }
+
+    memset(snp_cpuid_info, 0, sizeof(*snp_cpuid_info));
+
+    for (i = 0; i < kvm_cpuid_info->cpuid.nent; i++) {
+        const struct kvm_cpuid_entry2 *kvm_cpuid_entry;
+        SnpCpuidFunc *snp_cpuid_entry;
+
+        kvm_cpuid_entry = &kvm_cpuid_info->entries[i];
+        snp_cpuid_entry = &snp_cpuid_info->entries[i];
+
+        snp_cpuid_entry->eax_in = kvm_cpuid_entry->function;
+        if (kvm_cpuid_entry->flags == KVM_CPUID_FLAG_SIGNIFCANT_INDEX) {
+            snp_cpuid_entry->ecx_in = kvm_cpuid_entry->index;
+        }
+        snp_cpuid_entry->eax = kvm_cpuid_entry->eax;
+        snp_cpuid_entry->ebx = kvm_cpuid_entry->ebx;
+        snp_cpuid_entry->ecx = kvm_cpuid_entry->ecx;
+        snp_cpuid_entry->edx = kvm_cpuid_entry->edx;
+
+        /*
+         * Guest kernels will calculate EBX themselves using the 0xD
+         * subfunctions corresponding to the individual XSAVE areas, so only
+         * encode the base XSAVE size in the initial leaves, corresponding
+         * to the initial XCR0=1 state.
+         */
+        if (snp_cpuid_entry->eax_in == 0xD &&
+            (snp_cpuid_entry->ecx_in == 0x0 || snp_cpuid_entry->ecx_in == 0x1)) {
+            snp_cpuid_entry->ebx = 0x240;
+            snp_cpuid_entry->xcr0_in = 1;
+            snp_cpuid_entry->xss_in = 0;
+        }
+    }
+
+    snp_cpuid_info->count = i;
+
+    return 0;
+}
+
+static int
+snp_launch_update_cpuid(uint32_t cpuid_addr, void *hva, uint32_t cpuid_len)
+{
+    KvmCpuidInfo kvm_cpuid_info = {0};
+    SnpCpuidInfo snp_cpuid_info;
+    CPUState *cs = first_cpu;
+    int ret;
+    uint32_t i = 0;
+
+    assert(sizeof(snp_cpuid_info) <= cpuid_len);
+
+    /* get the cpuid list from KVM */
+    do {
+        kvm_cpuid_info.cpuid.nent = ++i;
+        ret = kvm_vcpu_ioctl(cs, KVM_GET_CPUID2, &kvm_cpuid_info);
+    } while (ret == -E2BIG);
+
+    if (ret) {
+        error_report("SEV-SNP: unable to query CPUID values for CPU: '%s'",
+                     strerror(-ret));
+        return 1;
+    }
+
+    ret = sev_snp_cpuid_info_fill(&snp_cpuid_info, &kvm_cpuid_info);
+    if (ret) {
+        error_report("SEV-SNP: failed to generate CPUID table information");
+        return 1;
+    }
+
+    memcpy(hva, &snp_cpuid_info, sizeof(snp_cpuid_info));
+
+    return snp_launch_update_data(cpuid_addr, hva, cpuid_len,
+                                  KVM_SEV_SNP_PAGE_TYPE_CPUID);
+}
+
 static int
 snp_metadata_desc_to_page_type(int desc_type)
 {
@@ -1053,7 +1208,12 @@ snp_populate_metadata_pages(SevSnpGuestState *sev_snp,
             exit(1);
         }
 
-        ret = snp_launch_update_data(desc->base, hva, desc->len, type);
+        if (type == KVM_SEV_SNP_PAGE_TYPE_CPUID) {
+            ret = snp_launch_update_cpuid(desc->base, hva, desc->len);
+        } else {
+            ret = snp_launch_update_data(desc->base, hva, desc->len, type);
+        }
+
         if (ret) {
             error_report("%s: Failed to add metadata page gpa 0x%x+%x type %d",
                          __func__, desc->base, desc->len, desc->type);