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limitations.md

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Limitations

  • When forking within an application it is not valid for a cryptographic operation to be started in the parent process, and completed in the child process.

  • Only one level of forking is permitted, if a child process forks again then the Intel® QAT OpenSSL* Engine will not be available in that forked process.

  • Event driven mode of polling operation is not supported in the FreeBSD Operating system or in the qatlib RPM.

  • qat_contig_mem memory driver is not supported when running under FreeBSD Operating system or in the qatlib RPM. The default is to use the USDM memory driver supplied as part of the Intel® QAT Driver.

  • SM2, SM3 & SM4 application testing is done using BabaSSL only since OpenSSL doesn't support SMx cipher suites.

  • QAT Engine doesn't support ENCRYPT_THEN_MAC(default) mode of operation meaning when Encrypt then MAC is negotiated for symmetric ciphers say AES-CBC, the requests will not get offloaded via QAT_HW, instead uses OpenSSL SW. Disable ENCRYPT_THEN_MAC with the flag SSL_OP_NO_ENCRYPT_THEN_MAC programmatically using SSL_CTX_set_options() to offload symmetric chained ciphers via QAT_HW. Please note disabling ENCRYPT_THEN_MAC has security implications.

  • Support for cipher AES-128-CBC-HMAC-SHA1 and its related ciphers was broken in release OpenSSL* 1.1.1d. This was later fixed in OpenSSL* 1.1.1e release.

  • OpenSSL 1.1.1n and OpenSSL3.0.2 introduced misleading error message(undefined symbol: EVP_PKEY_get_base_id) during engine load which can be ignored as it is not a real failure. This is later fixed in OpenSSL* 1.1.1o and OpenSSL* 3.0.3 release.

  • X25519/X448 support is available only from version 4.9 of the Intel® QAT driver for Linux. Use --disable-qat_hw_ecx in the Intel® QAT OpenSSL* Engine configure when building against earlier versions of the Linux driver.

  • Support for qaeMemFreeNonZeroNUMA() USDM API is available only from version 4.10 of the Intel® QAT driver for Linux. Use --with-cc-opt="-DQAT_HW_DISABLE_NONZERO_MEMFREE" in the Intel® QAT OpenSSL* Engine configuration when building against earlier versions of the Linux driver.

  • From version 4.19 and later of Intel® QAT driver for Linux, legacy or insecure algorithms such as DH, DSA, SHA1, RSA keysizes < 2048, EC curves < 256 bits are disabled by default hence there will be algo unsupported failures in the relevant ciphers. Driver needs to be built with flag "--enable-legacy-algorithms" to enable those algorithm support.

  • QAT Engine built for OpenSSL3.0 is only compatible with dependent libraries also linked with OpenSSL3.0 libraries due to OpenSSL#17112. Same applies for OpenSSL 1.1.1.

  • SM4-GCM and SM4-CCM are only supported with BabaSSL versions based on OpenSSL 1.1.1. They are not supported with OpenSSL 1.1.1, OpenSSL 3.0 and BabaSSL versions based on OpenSSL 3.0.

  • HKDF based on SM3 is not supported in QAT_HW, The request will fallback to OpenSSL software if fallback been enabled otherwise failures are observed.

  • There is a limitation with thread specific USDM: memory allocated in one thread should be freed only by the thread which allocates it. When the QAT driver is configured with --enable-icp-thread-specific-usdm, and when QAT_engine is used as the default OpenSSL engine, it is required that OPENSSL_init_ssl() be called from the same thread that calls OPENSSL_cleanup(). Incorrect cleanup can lead to a segmentation fault (segfault). Also, memory allocated in a thread is freed automatically when the thread exits/terminates, even if the user does not explicitly free the memory.

  • SVM is not supported with BoringSSL library and KPT.

  • AES-CCM ciphers are not enabled in OpenSSL by default. Need to enable it manually using the openssl.cnf file.

    Example:

  openssl_conf = cipher_conf

  [cipher_conf]
  ssl_conf = cipher_sect

  [cipher_sect]
  system_default = system_cipher_sect

  [system_cipher_sect]
  Cipherstring = ALL
  Ciphersuites = TLS_AES_128_CCM_8_SHA256:TLS_AES_128_CCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256

Known Issues

Functional

  • AES-CBC-HMAC-SHA chained ciphers does not support pipeline feature when built with OpenSSL 3.0 as the corresponding support is not available in OpenSSL 3.0 - OpenSSL#18298
  • There is an issue in sshd daemon application when using the QAT for default openssl. sshd looks to be closing the file descriptors associated with QAT engine and driver after initialising openssl. Similar issue was present which prevents the ability to ssh out of the system using the QAT engine in versions of the ssh application before OpenSSH 8.7. The issue has been fixed with this commit c9f7bba . This update can be applied to sshd to work-around the issue.
  • Known issue with QAT_SW SM2 in ntls mode since QAT_SW SM2 doesn't have plain sign and verify operation support in engine. Disable QAT_SW SM2 to workaround the issue with ntls. No issues with TLS mode since it uses digestsign and digestverify which is supported.
  • Known issue in Software fallback with OpenSSL3.0 Engine(only) when disabled via co-existence algo bitmap for algorithms PRF, HKDF, SM2 & SM3. QAT_HW PRF and QAT_HW HKDF are not accelerated in OpenSSL 3.0 engine due to the issue OpenSSL#21622

Performance

  • There is known performance scaling issue (performance drop with threads >32) with ECDSA Ciphers in the QAT Software acceleration using multithread mode in the Haproxy application. This issue is not observed when using RSA ciphers or in multi-process mode.

  • SM3 is disabled by default due to performance drop observed in multithread scenario for all ciphers suites due to the additional locks at engine_table_select introduced by engine digest registration in OpenSSL - OpenSSL#18509

  • In Co-Existence mode, performance will drop for PKE algorithms compared with QAT_SW when process number >= 64.

  • Note regarding multithreaded performance with OpenSSL:** In some cases, using QAT_Engine with OpenSSL at higher thread counts can produce worse performance, due to issues in the way OpenSSL handles higher thread counts. Check for native_queued_spin_lock_slowpath() consuming CPU process idle time, and see the OpenSSL GitHub issues and web articles below.

  • Nginx Handshake Performance in OpenSSL3.0 is slightly slower compared to OpenSSL 1.1.1. The same behaviour is observed in OpenSSL_SW as well OpenSSL#21833.

  • Performance scaling is not linear in QAT2.0 supported platforms in ECDSA and chacha-poly algorithms.

    Articles: