crypto: query gcrypt for cipher availability

Just because a cipher is defined in the gcrypt header file, does not
imply that it can be used. Distros can filter the list of ciphers when
building gcrypt. For example, RHEL-9 disables the SM4 cipher. It is
also possible that running in FIPS mode might dynamically change what
ciphers are available at runtime.

qcrypto_cipher_supports must therefore query gcrypt directly to check
for cipher availability.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto/cipher-gcrypt.c.inc

@@ -93,6 +93,11 @@ bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg,
         return false;
     }
 
+    if (gcry_cipher_algo_info(qcrypto_cipher_alg_to_gcry_alg(alg),
+                              GCRYCTL_TEST_ALGO, NULL, NULL) != 0) {
+        return false;
+    }
+
     switch (mode) {
     case QCRYPTO_CIPHER_MODE_ECB:
     case QCRYPTO_CIPHER_MODE_CBC: