Hello,

Some AVX-512 and AVX-512VL assembly code for ChaCha20 is zeroing registers that should be preserved by the callee on Win64 platforms (as per Microsoft doc). More precisely, ChaCha20_avx512 and ChaCha20_avx512vl save the nonvolatile xmm6 and xmm7 registers properly, but they do not for xmm8-xmm15. In their teardown (the done part), they clear all YMM registers with vzeroall, zeroing the remaining nonvolatile XMM registers.

This issue has been seen with OpenSSL 1.1.1k, with a corrupted caller state after an OpenSSL call.