crypto/cipher: Add setaad/gettag for AEAD modes

AEAD modes such as GCM authenticate optional associated data (AAD) and
produce an authentication tag, which the block-cipher encrypt/decrypt
interface cannot express. Add qcrypto_cipher_setaad() and
qcrypto_cipher_gettag() plus the matching backend driver hooks. The
generic front-end reports an error when the selected mode's driver does
not implement them, so calling them on a non-AEAD mode fails cleanly.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Kane Chen <kane_chen@aspeedtech.com>
Link: https://lore.kernel.org/qemu-devel/20260811060115.1849266-9-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

crypto/cipher.c

@@ -205,6 +205,37 @@ int qcrypto_cipher_setiv(QCryptoCipher *cipher,
 }
 
 
+int qcrypto_cipher_setaad(QCryptoCipher *cipher,
+                          const uint8_t *aad, size_t len,
+                          Error **errp)
+{
+    const QCryptoCipherDriver *drv = cipher->driver;
+
+    if (!drv->cipher_setaad) {
+        error_setg(errp, "The cipher mode does not support associated data");
+        return -1;
+    }
+
+    return drv->cipher_setaad(cipher, aad, len, errp);
+}
+
+
+int qcrypto_cipher_gettag(QCryptoCipher *cipher,
+                          uint8_t *tag, size_t len,
+                          Error **errp)
+{
+    const QCryptoCipherDriver *drv = cipher->driver;
+
+    if (!drv->cipher_gettag) {
+        error_setg(errp,
+                   "The cipher mode does not produce an authentication tag");
+        return -1;
+    }
+
+    return drv->cipher_gettag(cipher, tag, len, errp);
+}
+
+
 void qcrypto_cipher_free(QCryptoCipher *cipher)
 {
     if (cipher) {

crypto/cipherpriv.h

@@ -34,6 +34,14 @@ struct QCryptoCipherDriver {
                         const uint8_t *iv, size_t niv,
                         Error **errp);
 
+    int (*cipher_setaad)(QCryptoCipher *cipher,
+                         const uint8_t *aad, size_t len,
+                         Error **errp);
+
+    int (*cipher_gettag)(QCryptoCipher *cipher,
+                         uint8_t *tag, size_t len,
+                         Error **errp);
+
     void (*cipher_free)(QCryptoCipher *cipher);
 };
 

include/crypto/cipher.h

@@ -235,4 +235,40 @@ int qcrypto_cipher_setiv(QCryptoCipher *cipher,
                          const uint8_t *iv, size_t niv,
                          Error **errp);
 
+/**
+ * qcrypto_cipher_setaad:
+ * @cipher: the cipher object
+ * @aad: the associated data to authenticate
+ * @len: the length of @aad
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * For AEAD modes such as GCM, feed the associated data (AAD) that is
+ * authenticated but not encrypted. It must be called after
+ * qcrypto_cipher_setiv() and before the first encrypt/decrypt call. It is
+ * an error to call this on a mode that is not an AEAD mode.
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int qcrypto_cipher_setaad(QCryptoCipher *cipher,
+                          const uint8_t *aad, size_t len,
+                          Error **errp);
+
+/**
+ * qcrypto_cipher_gettag:
+ * @cipher: the cipher object
+ * @tag: buffer to receive the authentication tag
+ * @len: the length of @tag
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * For AEAD modes such as GCM, read back the authentication tag computed
+ * over the associated data and the message. It must be called after the
+ * encrypt/decrypt operation. It is an error to call this on a mode that is
+ * not an AEAD mode.
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int qcrypto_cipher_gettag(QCryptoCipher *cipher,
+                          uint8_t *tag, size_t len,
+                          Error **errp);
+
 #endif /* QCRYPTO_CIPHER_H */