From 70542b53cd09fcae26c3579cd84bcee39a4b8a57 Mon Sep 17 00:00:00 2001
From: Tom Thorogood <me+google@tomthorogood.co.uk>
Date: Wed, 2 May 2018 20:35:38 +0930
Subject: [PATCH] chacha20poly1305: correct AVX2 feature detection

CL 110355 switched out the adhoc cpu feature detection for x/sys/cpu, in
doing so the AVX2 check was broken. The assembly code uses MULX which is
part of BMI2.

Updates golang/go#24843
---
 chacha20poly1305/chacha20poly1305_amd64.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/chacha20poly1305/chacha20poly1305_amd64.go b/chacha20poly1305/chacha20poly1305_amd64.go
index ff21390d32..07d18a32f7 100644
--- a/chacha20poly1305/chacha20poly1305_amd64.go
+++ b/chacha20poly1305/chacha20poly1305_amd64.go
@@ -20,7 +20,7 @@ func chacha20Poly1305Seal(dst []byte, key []uint32, src, ad []byte)
 
 var (
 	useASM  = cpu.X86.HasSSSE3
-	useAVX2 = cpu.X86.HasAVX2
+	useAVX2 = cpu.X86.HasAVX2 && cpu.X86.HasBMI2
 )
 
 // setupState writes a ChaCha20 input matrix to state. See