[PULL 14/37] crypto/x509-utils: Add helper functions for DIAG 508 subcode 1

[Eric Farman <farman@linux.ibm.com>]

From: Zhuoying Cai <zycai@linux.ibm.com>

Introduce helper functions to support signature verification required by
DIAG 508 subcode 1:

qcrypto_pkcs7_convert_sig_pem() – converts a signature from DER to PEM format
qcrypto_x509_verify_sig() – verifies the provided data against the given signature

These functions enable basic signature verification support.

Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260730214624.2328883-13-zycai@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 crypto/x509-utils.c         | 108 ++++++++++++++++++++++++++++++++++++
 include/crypto/x509-utils.h |  41 ++++++++++++++
 2 files changed, 149 insertions(+)

diff --git a/crypto/x509-utils.c b/crypto/x509-utils.c
index 543fc3007d..e4767f9838 100644
--- a/crypto/x509-utils.c
+++ b/crypto/x509-utils.c
@@ -16,6 +16,7 @@
 #include <gnutls/gnutls.h>
 #include <gnutls/crypto.h>
 #include <gnutls/x509.h>
+#include <gnutls/pkcs7.h>
 
 static const int qcrypto_to_gnutls_hash_alg_map[QCRYPTO_HASH_ALGO__MAX] = {
     [QCRYPTO_HASH_ALGO_MD5] = GNUTLS_DIG_MD5,
@@ -336,6 +337,96 @@ int qcrypto_x509_check_ecc_curve_p521(uint8_t *cert, size_t size, Error **errp)
     return curve_id == GNUTLS_ECC_CURVE_SECP521R1;
 }
 
+int qcrypto_pkcs7_convert_sig_pem(uint8_t *sig, size_t sig_size,
+                                  uint8_t **result, size_t *resultlen,
+                                  Error **errp)
+{
+    int ret = -1;
+    int rc;
+    gnutls_pkcs7_t signature;
+    gnutls_datum_t sig_datum_der = {.data = sig, .size = sig_size};
+    gnutls_datum_t sig_datum_pem = {.data = NULL, .size = 0};
+
+    rc = gnutls_pkcs7_init(&signature);
+    if (rc < 0) {
+        error_setg(errp, "Failed to initialize pkcs7 data: %s", gnutls_strerror(rc));
+        return ret;
+    }
+
+    rc = gnutls_pkcs7_import(signature, &sig_datum_der, GNUTLS_X509_FMT_DER);
+    if (rc != 0) {
+        error_setg(errp, "Failed to import signature: %s", gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    rc = gnutls_pkcs7_export2(signature, GNUTLS_X509_FMT_PEM, &sig_datum_pem);
+    if (rc != 0) {
+        error_setg(errp, "Failed to convert signature to PEM format: %s",
+                   gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    *resultlen = sig_datum_pem.size;
+    *result = g_memdup2(sig_datum_pem.data, sig_datum_pem.size);
+
+    ret = 0;
+
+cleanup:
+    gnutls_pkcs7_deinit(signature);
+    g_free(sig_datum_pem.data);
+    return ret;
+}
+
+int qcrypto_x509_verify_sig(uint8_t *cert, size_t cert_size,
+                            uint8_t *comp, size_t comp_size,
+                            uint8_t *sig, size_t sig_size, Error **errp)
+{
+    int rc;
+    int ret = -1;
+    gnutls_x509_crt_t crt = NULL;
+    gnutls_pkcs7_t signature = NULL;
+    gnutls_datum_t cert_datum = {.data = cert, .size = cert_size};
+    gnutls_datum_t data_datum = {.data = comp, .size = comp_size};
+    gnutls_datum_t sig_datum = {.data = sig, .size = sig_size};
+
+    rc = gnutls_x509_crt_init(&crt);
+    if (rc < 0) {
+        error_setg(errp, "Failed to initialize certificate: %s", gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    rc = gnutls_x509_crt_import(crt, &cert_datum, GNUTLS_X509_FMT_PEM);
+    if (rc != 0) {
+        error_setg(errp, "Failed to import certificate: %s", gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    rc = gnutls_pkcs7_init(&signature);
+    if (rc < 0) {
+        error_setg(errp, "Failed to initialize pkcs7 data: %s", gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    rc = gnutls_pkcs7_import(signature, &sig_datum, GNUTLS_X509_FMT_PEM);
+    if (rc != 0) {
+        error_setg(errp, "Failed to import signature: %s", gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    rc = gnutls_pkcs7_verify_direct(signature, crt, 0, &data_datum, 0);
+    if (rc != 0) {
+        error_setg(errp, "Failed to verify signature: %s", gnutls_strerror(rc));
+        goto cleanup;
+    }
+
+    ret = 0;
+
+cleanup:
+    gnutls_x509_crt_deinit(crt);
+    gnutls_pkcs7_deinit(signature);
+    return ret;
+}
+
 #else /* ! CONFIG_GNUTLS */
 
 int qcrypto_get_x509_cert_fingerprint(uint8_t *cert, size_t size,
@@ -379,4 +470,21 @@ int qcrypto_x509_check_ecc_curve_p521(uint8_t *cert, size_t size, Error **errp)
     return -1;
 }
 
+int qcrypto_pkcs7_convert_sig_pem(uint8_t *sig, size_t sig_size,
+                                  uint8_t **result,
+                                  size_t *resultlen,
+                                  Error **errp)
+{
+    error_setg(errp, "GNUTLS is required to export pkcs7 signature");
+    return -1;
+}
+
+int qcrypto_x509_verify_sig(uint8_t *cert, size_t cert_size,
+                            uint8_t *comp, size_t comp_size,
+                            uint8_t *sig, size_t sig_size, Error **errp)
+{
+    error_setg(errp, "GNUTLS is required for signature-verification support");
+    return -1;
+}
+
 #endif /* ! CONFIG_GNUTLS */
diff --git a/include/crypto/x509-utils.h b/include/crypto/x509-utils.h
index fcace73c49..c256d7bfad 100644
--- a/include/crypto/x509-utils.h
+++ b/include/crypto/x509-utils.h
@@ -91,4 +91,45 @@ int qcrypto_x509_get_cert_key_id(uint8_t *cert, size_t size,
  */
 int qcrypto_x509_check_ecc_curve_p521(uint8_t *cert, size_t size, Error **errp);
 
+/**
+ * qcrypto_pkcs7_convert_sig_pem
+ * @sig: pointer to the PKCS#7 signature in DER format
+ * @sig_size: size of the signature
+ * @result: output location for the allocated buffer for the signature in
+ *          PEM format
+ *          (the function allocates memory which must be freed by the caller)
+ * @resultlen: pointer to the size of the buffer
+ *              (will be updated with the actual size of the PEM-encoded
+ *               signature)
+ * @errp: error pointer
+ *
+ * Convert given PKCS#7 @sig from DER to PEM format.
+ *
+ * Returns: 0 if PEM-encoded signature was successfully stored in @result,
+ *         -1 on error.
+ */
+int qcrypto_pkcs7_convert_sig_pem(uint8_t *sig, size_t sig_size,
+                                  uint8_t **result,
+                                  size_t *resultlen,
+                                  Error **errp);
+
+/**
+ * qcrypto_x509_verify_sig
+ * @cert: pointer to the raw certificate data
+ * @cert_size: size of the certificate
+ * @comp: pointer to the component to be verified
+ * @comp_size: size of the component
+ * @sig: pointer to the signature
+ * @sig_size: size of the signature
+ * @errp: error pointer
+ *
+ * Verify the provided @comp against the @sig and @cert.
+ *
+ * Returns: 0 on success,
+ *         -1 on error.
+ */
+int qcrypto_x509_verify_sig(uint8_t *cert, size_t cert_size,
+                            uint8_t *comp, size_t comp_size,
+                            uint8_t *sig, size_t sig_size, Error **errp);
+
 #endif
-- 
2.55.0