[release-branch.go1.13] crypto/ecdsa: remove s390x assembly

This is a revert of CL 174437 and equivalent to CL 201360.

The size of the params block passed into the KDSA instruction is
incorrect and this appears to result in out-of-bounds writes
that cause a panic in the crypto/x509 tests when run on a machine
that supports KDSA.

Remove this assembly for now. We can revisit the use of the KDSA
instruction in a future release.

Fixes #34928.

Change-Id: I7ad2fe9714b47ad04abc25f18aa235b9d2aef062
Reviewed-on: https://go-review.googlesource.com/c/go/+/201361
Run-TryBot: Michael Munday <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: mundaym

src/crypto/ecdsa/ecdsa.go

@@ -189,21 +189,14 @@ func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err err
 
 	// See [NSA] 3.4.1
 	c := priv.PublicKey.Curve
-	e := hashToInt(hash, c)
-	r, s, err = sign(priv, &csprng, c, e)
-	return
-}
-
-func signGeneric(priv *PrivateKey, csprng *cipher.StreamReader, c elliptic.Curve, e *big.Int) (r, s *big.Int, err error) {
 	N := c.Params().N
 	if N.Sign() == 0 {
 		return nil, nil, errZeroParam
 	}
-
 	var k, kInv *big.Int
 	for {
 		for {
-			k, err = randFieldElement(c, *csprng)
+			k, err = randFieldElement(c, csprng)
 			if err != nil {
 				r = nil
 				return
@@ -221,6 +214,8 @@ func signGeneric(priv *PrivateKey, csprng *cipher.StreamReader, c elliptic.Curve
 				break
 			}
 		}
+
+		e := hashToInt(hash, c)
 		s = new(big.Int).Mul(priv.D, r)
 		s.Add(s, e)
 		s.Mul(s, kInv)
@@ -229,6 +224,7 @@ func signGeneric(priv *PrivateKey, csprng *cipher.StreamReader, c elliptic.Curve
 			break
 		}
 	}
+
 	return
 }
 
@@ -246,12 +242,8 @@ func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool {
 		return false
 	}
 	e := hashToInt(hash, c)
-	return verify(pub, c, e, r, s)
-}
 
-func verifyGeneric(pub *PublicKey, c elliptic.Curve, e, r, s *big.Int) bool {
 	var w *big.Int
-	N := c.Params().N
 	if in, ok := c.(invertible); ok {
 		w = in.Inverse(s)
 	} else {