From https://pubs.opengroup.org/onlinepubs/9799919799/functions/g...

“The intended use of this function is to create a seed for other pseudo-random number generators”

So, if I were to use genentropy() in a POSIX-compliant way, I would need to do what I already do: Use my own pseudo-random number generator.

The Debian openssl disaster (CVE 2008-0166, I remember it well) was caused because someone incorrectly patched secure code: Since the code used uninitialized memory as one of many entropy sources, which causes Valgrind to complain, they patched the code to not use uninitialized memory for entropy, but then accidentally disabled all other sources of entropy (except the 16-bit PID). It was caused because the person making the patch didn’t fully understand why it was a good idea to, in that context, use code which Valgrind complained about. [1]

As an aside, here’s how I deal with those Valgrind errors:

  #ifdef VALGRIND_NOERRORS
        /* Valgrind reports our intentional use of values of uncleared
         * allocated memory as one source of entropy as an error, so we
         * allow it to be disabled for Valgrind testing */
        memset(noise,0,512);
  #endif /* VALGRIND_NOERRORS */

[1] Debian has a lot of inflexible policies like this which can cause problems. Another issue Debian has is they have a policy a given piece of code must always compile to the same binary on a given architecture. That isn’t true with the unpatched version of my code, because the hash compression routine uses a 32-bit random number generated at compile time to avoid hash collision attacks (it also uses another 32-bit random number at runtime, and I make sure the hash compression values are never visible). So the Debian version of my code was forced to be patched to be less secure.