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-rw-r--r--src/tpm.c391
1 files changed, 391 insertions, 0 deletions
diff --git a/src/tpm.c b/src/tpm.c
new file mode 100644
index 0000000..3e09bca
--- /dev/null
+++ b/src/tpm.c
@@ -0,0 +1,391 @@
+/*
+ * Copyright (c) 2021 Yubico AB. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+/*
+ * Trusted Platform Module (TPM) 2.0 attestation support. Documentation
+ * references are relative to revision 01.38 of the TPM 2.0 specification.
+ */
+
+#include <openssl/sha.h>
+
+#include "packed.h"
+#include "fido.h"
+
+/* Part 1, 4.89: TPM_GENERATED_VALUE */
+#define TPM_MAGIC 0xff544347
+
+/* Part 2, 6.3: TPM_ALG_ID */
+#define TPM_ALG_RSA 0x0001
+#define TPM_ALG_SHA256 0x000b
+#define TPM_ALG_NULL 0x0010
+#define TPM_ALG_ECC 0x0023
+
+/* Part 2, 6.4: TPM_ECC_CURVE */
+#define TPM_ECC_P256 0x0003
+
+/* Part 2, 6.9: TPM_ST_ATTEST_CERTIFY */
+#define TPM_ST_CERTIFY 0x8017
+
+/* Part 2, 8.3: TPMA_OBJECT */
+#define TPMA_RESERVED 0xfff8f309 /* reserved bits; must be zero */
+#define TPMA_FIXED 0x00000002 /* object has fixed hierarchy */
+#define TPMA_CLEAR 0x00000004 /* object persists */
+#define TPMA_FIXED_P 0x00000010 /* object has fixed parent */
+#define TPMA_SENSITIVE 0x00000020 /* data originates within tpm */
+#define TPMA_SIGN 0x00040000 /* object may sign */
+
+/* Part 2, 10.4.2: TPM2B_DIGEST */
+PACKED_TYPE(tpm_sha256_digest_t,
+struct tpm_sha256_digest {
+ uint16_t size; /* sizeof(body) */
+ uint8_t body[32];
+})
+
+/* Part 2, 10.4.3: TPM2B_DATA */
+PACKED_TYPE(tpm_sha1_data_t,
+struct tpm_sha1_data {
+ uint16_t size; /* sizeof(body) */
+ uint8_t body[20];
+})
+
+/* Part 2, 10.5.3: TPM2B_NAME */
+PACKED_TYPE(tpm_sha256_name_t,
+struct tpm_sha256_name {
+ uint16_t size; /* sizeof(alg) + sizeof(body) */
+ uint16_t alg; /* TPM_ALG_SHA256 */
+ uint8_t body[32];
+})
+
+/* Part 2, 10.11.1: TPMS_CLOCK_INFO */
+PACKED_TYPE(tpm_clock_info_t,
+struct tpm_clock_info {
+ uint64_t timestamp_ms;
+ uint32_t reset_count; /* obfuscated by tpm */
+ uint32_t restart_count; /* obfuscated by tpm */
+ uint8_t safe; /* 1 if timestamp_ms is current */
+})
+
+/* Part 2, 10.12.8 TPMS_ATTEST */
+PACKED_TYPE(tpm_sha1_attest_t,
+struct tpm_sha1_attest {
+ uint32_t magic; /* TPM_MAGIC */
+ uint16_t type; /* TPM_ST_ATTEST_CERTIFY */
+ tpm_sha256_name_t signer; /* full tpm path of signing key */
+ tpm_sha1_data_t data; /* signed sha1 */
+ tpm_clock_info_t clock;
+ uint64_t fwversion; /* obfuscated by tpm */
+ tpm_sha256_name_t name; /* sha256 of tpm_rs256_pubarea_t */
+ tpm_sha256_name_t qual_name; /* full tpm path of attested key */
+})
+
+/* Part 2, 11.2.4.5: TPM2B_PUBLIC_KEY_RSA */
+PACKED_TYPE(tpm_rs256_key_t,
+struct tpm_rs256_key {
+ uint16_t size; /* sizeof(body) */
+ uint8_t body[256];
+})
+
+/* Part 2, 11.2.5.1: TPM2B_ECC_PARAMETER */
+PACKED_TYPE(tpm_es256_coord_t,
+struct tpm_es256_coord {
+ uint16_t size; /* sizeof(body) */
+ uint8_t body[32];
+})
+
+/* Part 2, 11.2.5.2: TPMS_ECC_POINT */
+PACKED_TYPE(tpm_es256_point_t,
+struct tpm_es256_point {
+ tpm_es256_coord_t x;
+ tpm_es256_coord_t y;
+})
+
+/* Part 2, 12.2.3.5: TPMS_RSA_PARMS */
+PACKED_TYPE(tpm_rs256_param_t,
+struct tpm_rs256_param {
+ uint16_t symmetric; /* TPM_ALG_NULL */
+ uint16_t scheme; /* TPM_ALG_NULL */
+ uint16_t keybits; /* 2048 */
+ uint32_t exponent; /* zero (meaning 2^16 + 1) */
+})
+
+/* Part 2, 12.2.3.6: TPMS_ECC_PARMS */
+PACKED_TYPE(tpm_es256_param_t,
+struct tpm_es256_param {
+ uint16_t symmetric; /* TPM_ALG_NULL */
+ uint16_t scheme; /* TPM_ALG_NULL */
+ uint16_t curve_id; /* TPM_ECC_P256 */
+ uint16_t kdf; /* TPM_ALG_NULL */
+})
+
+/* Part 2, 12.2.4: TPMT_PUBLIC */
+PACKED_TYPE(tpm_rs256_pubarea_t,
+struct tpm_rs256_pubarea {
+ uint16_t alg; /* TPM_ALG_RSA */
+ uint16_t hash; /* TPM_ALG_SHA256 */
+ uint32_t attr;
+ tpm_sha256_digest_t policy; /* must be present? */
+ tpm_rs256_param_t param;
+ tpm_rs256_key_t key;
+})
+
+/* Part 2, 12.2.4: TPMT_PUBLIC */
+PACKED_TYPE(tpm_es256_pubarea_t,
+struct tpm_es256_pubarea {
+ uint16_t alg; /* TPM_ALG_ECC */
+ uint16_t hash; /* TPM_ALG_SHA256 */
+ uint32_t attr;
+ tpm_sha256_digest_t policy; /* must be present? */
+ tpm_es256_param_t param;
+ tpm_es256_point_t point;
+})
+
+static int
+get_signed_sha1(tpm_sha1_data_t *dgst, const fido_blob_t *authdata,
+ const fido_blob_t *clientdata)
+{
+ const EVP_MD *md = NULL;
+ EVP_MD_CTX *ctx = NULL;
+ int ok = -1;
+
+ if ((dgst->size = sizeof(dgst->body)) != SHA_DIGEST_LENGTH ||
+ (md = EVP_sha1()) == NULL ||
+ (ctx = EVP_MD_CTX_new()) == NULL ||
+ EVP_DigestInit_ex(ctx, md, NULL) != 1 ||
+ EVP_DigestUpdate(ctx, authdata->ptr, authdata->len) != 1 ||
+ EVP_DigestUpdate(ctx, clientdata->ptr, clientdata->len) != 1 ||
+ EVP_DigestFinal_ex(ctx, dgst->body, NULL) != 1) {
+ fido_log_debug("%s: sha1", __func__);
+ goto fail;
+ }
+
+ ok = 0;
+fail:
+ EVP_MD_CTX_free(ctx);
+
+ return (ok);
+}
+
+static int
+get_signed_name(tpm_sha256_name_t *name, const fido_blob_t *pubarea)
+{
+ name->alg = TPM_ALG_SHA256;
+ name->size = sizeof(name->alg) + sizeof(name->body);
+ if (sizeof(name->body) != SHA256_DIGEST_LENGTH ||
+ SHA256(pubarea->ptr, pubarea->len, name->body) != name->body) {
+ fido_log_debug("%s: sha256", __func__);
+ return -1;
+ }
+
+ return 0;
+}
+
+static void
+bswap_rs256_pubarea(tpm_rs256_pubarea_t *x)
+{
+ x->alg = htobe16(x->alg);
+ x->hash = htobe16(x->hash);
+ x->attr = htobe32(x->attr);
+ x->policy.size = htobe16(x->policy.size);
+ x->param.symmetric = htobe16(x->param.symmetric);
+ x->param.scheme = htobe16(x->param.scheme);
+ x->param.keybits = htobe16(x->param.keybits);
+ x->key.size = htobe16(x->key.size);
+}
+
+static void
+bswap_es256_pubarea(tpm_es256_pubarea_t *x)
+{
+ x->alg = htobe16(x->alg);
+ x->hash = htobe16(x->hash);
+ x->attr = htobe32(x->attr);
+ x->policy.size = htobe16(x->policy.size);
+ x->param.symmetric = htobe16(x->param.symmetric);
+ x->param.scheme = htobe16(x->param.scheme);
+ x->param.curve_id = htobe16(x->param.curve_id);
+ x->param.kdf = htobe16(x->param.kdf);
+ x->point.x.size = htobe16(x->point.x.size);
+ x->point.y.size = htobe16(x->point.y.size);
+}
+
+static void
+bswap_sha1_certinfo(tpm_sha1_attest_t *x)
+{
+ x->magic = htobe32(x->magic);
+ x->type = htobe16(x->type);
+ x->signer.size = htobe16(x->signer.size);
+ x->data.size = htobe16(x->data.size);
+ x->name.alg = htobe16(x->name.alg);
+ x->name.size = htobe16(x->name.size);
+}
+
+static int
+check_rs256_pubarea(const fido_blob_t *buf, const rs256_pk_t *pk)
+{
+ const tpm_rs256_pubarea_t *actual;
+ tpm_rs256_pubarea_t expected;
+ int ok;
+
+ if (buf->len != sizeof(*actual)) {
+ fido_log_debug("%s: buf->len=%zu", __func__, buf->len);
+ return -1;
+ }
+ actual = (const void *)buf->ptr;
+
+ memset(&expected, 0, sizeof(expected));
+ expected.alg = TPM_ALG_RSA;
+ expected.hash = TPM_ALG_SHA256;
+ expected.attr = be32toh(actual->attr);
+ expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR);
+ expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN);
+ expected.policy = actual->policy;
+ expected.policy.size = sizeof(expected.policy.body);
+ expected.param.symmetric = TPM_ALG_NULL;
+ expected.param.scheme = TPM_ALG_NULL;
+ expected.param.keybits = 2048;
+ expected.param.exponent = 0; /* meaning 2^16+1 */
+ expected.key.size = sizeof(expected.key.body);
+ memcpy(&expected.key.body, &pk->n, sizeof(expected.key.body));
+ bswap_rs256_pubarea(&expected);
+
+ ok = timingsafe_bcmp(&expected, actual, sizeof(expected));
+ explicit_bzero(&expected, sizeof(expected));
+
+ return ok != 0 ? -1 : 0;
+}
+
+static int
+check_es256_pubarea(const fido_blob_t *buf, const es256_pk_t *pk)
+{
+ const tpm_es256_pubarea_t *actual;
+ tpm_es256_pubarea_t expected;
+ int ok;
+
+ if (buf->len != sizeof(*actual)) {
+ fido_log_debug("%s: buf->len=%zu", __func__, buf->len);
+ return -1;
+ }
+ actual = (const void *)buf->ptr;
+
+ memset(&expected, 0, sizeof(expected));
+ expected.alg = TPM_ALG_ECC;
+ expected.hash = TPM_ALG_SHA256;
+ expected.attr = be32toh(actual->attr);
+ expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR);
+ expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN);
+ expected.policy = actual->policy;
+ expected.policy.size = sizeof(expected.policy.body);
+ expected.param.symmetric = TPM_ALG_NULL;
+ expected.param.scheme = TPM_ALG_NULL; /* TCG Alg. Registry, 5.2.4 */
+ expected.param.curve_id = TPM_ECC_P256;
+ expected.param.kdf = TPM_ALG_NULL;
+ expected.point.x.size = sizeof(expected.point.x.body);
+ expected.point.y.size = sizeof(expected.point.y.body);
+ memcpy(&expected.point.x.body, &pk->x, sizeof(expected.point.x.body));
+ memcpy(&expected.point.y.body, &pk->y, sizeof(expected.point.y.body));
+ bswap_es256_pubarea(&expected);
+
+ ok = timingsafe_bcmp(&expected, actual, sizeof(expected));
+ explicit_bzero(&expected, sizeof(expected));
+
+ return ok != 0 ? -1 : 0;
+}
+
+static int
+check_sha1_certinfo(const fido_blob_t *buf, const fido_blob_t *clientdata_hash,
+ const fido_blob_t *authdata_raw, const fido_blob_t *pubarea)
+{
+ const tpm_sha1_attest_t *actual;
+ tpm_sha1_attest_t expected;
+ tpm_sha1_data_t signed_data;
+ tpm_sha256_name_t signed_name;
+ int ok = -1;
+
+ memset(&signed_data, 0, sizeof(signed_data));
+ memset(&signed_name, 0, sizeof(signed_name));
+
+ if (get_signed_sha1(&signed_data, authdata_raw, clientdata_hash) < 0 ||
+ get_signed_name(&signed_name, pubarea) < 0) {
+ fido_log_debug("%s: get_signed_sha1/name", __func__);
+ goto fail;
+ }
+ if (buf->len != sizeof(*actual)) {
+ fido_log_debug("%s: buf->len=%zu", __func__, buf->len);
+ goto fail;
+ }
+ actual = (const void *)buf->ptr;
+
+ memset(&expected, 0, sizeof(expected));
+ expected.magic = TPM_MAGIC;
+ expected.type = TPM_ST_CERTIFY;
+ expected.signer = actual->signer;
+ expected.signer.size = sizeof(expected.signer.alg) +
+ sizeof(expected.signer.body);
+ expected.data = signed_data;
+ expected.clock = actual->clock;
+ expected.clock.safe = 1;
+ expected.fwversion = actual->fwversion;
+ expected.name = signed_name;
+ expected.qual_name = actual->qual_name;
+ bswap_sha1_certinfo(&expected);
+
+ ok = timingsafe_bcmp(&expected, actual, sizeof(expected));
+fail:
+ explicit_bzero(&expected, sizeof(expected));
+ explicit_bzero(&signed_data, sizeof(signed_data));
+ explicit_bzero(&signed_name, sizeof(signed_name));
+
+ return ok != 0 ? -1 : 0;
+}
+
+int
+fido_get_signed_hash_tpm(fido_blob_t *dgst, const fido_blob_t *clientdata_hash,
+ const fido_blob_t *authdata_raw, const fido_attstmt_t *attstmt,
+ const fido_attcred_t *attcred)
+{
+ const fido_blob_t *pubarea = &attstmt->pubarea;
+ const fido_blob_t *certinfo = &attstmt->certinfo;
+
+ if (attstmt->alg != COSE_RS1) {
+ fido_log_debug("%s: unsupported alg %d", __func__,
+ attstmt->alg);
+ return -1;
+ }
+
+ switch (attcred->type) {
+ case COSE_ES256:
+ if (check_es256_pubarea(pubarea, &attcred->pubkey.es256) < 0) {
+ fido_log_debug("%s: check_es256_pubarea", __func__);
+ return -1;
+ }
+ break;
+ case COSE_RS256:
+ if (check_rs256_pubarea(pubarea, &attcred->pubkey.rs256) < 0) {
+ fido_log_debug("%s: check_rs256_pubarea", __func__);
+ return -1;
+ }
+ break;
+ default:
+ fido_log_debug("%s: unsupported type %d", __func__,
+ attcred->type);
+ return -1;
+ }
+
+ if (check_sha1_certinfo(certinfo, clientdata_hash, authdata_raw,
+ pubarea) < 0) {
+ fido_log_debug("%s: check_sha1_certinfo", __func__);
+ return -1;
+ }
+
+ if (dgst->len < SHA_DIGEST_LENGTH ||
+ SHA1(certinfo->ptr, certinfo->len, dgst->ptr) != dgst->ptr) {
+ fido_log_debug("%s: sha1", __func__);
+ return -1;
+ }
+ dgst->len = SHA_DIGEST_LENGTH;
+
+ return 0;
+}
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