2.7 How to disable hardware features

Libgcrypt makes use of certain hardware features. If the use of a feature is not desired it may be either be disabled by a program or globally using a configuration file. The currently supported features are

padlock-rng

padlock-aes

padlock-sha

padlock-mmul

intel-cpu

intel-bmi2

intel-ssse3

intel-pclmul

intel-aesni

intel-rdrand

intel-avx

intel-avx2

arm-neon

To disable a feature for all processes using Libgcrypt 1.6 or newer, create the file ‘/etc/gcrypt/hwf.deny’ and put each feature not to be used on a single line. Empty lines, white space, and lines prefixed with a hash mark are ignored. The file should be world readable.

To disable a feature specifically for a program that program must tell it Libgcrypt before before calling gcry_check_version. Example:(2)

  gcry_control (GCRYCTL_DISABLE_HWF, "intel-rdrand", NULL);

To print the list of active features you may use this command:

  mpicalc --print-config | grep ^hwflist: | tr : '\n' | tail -n +2

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