AES_GMAC_TAG_BITS
gcm_ctx->gcm_tag_len = CRYPTO_BITS2BYTES(AES_GMAC_TAG_BITS);
CTASSERT(sizeof (buf) >= CRYPTO_BITS2BYTES(AES_GMAC_TAG_BITS));
mac_len = CRYPTO_BITS2BYTES(AES_GMAC_TAG_BITS);