Index: openssl-1.1.1d/crypto/ec/ecx_meth.c
===================================================================
--- openssl-1.1.1d.orig/crypto/ec/ecx_meth.c
+++ openssl-1.1.1d/crypto/ec/ecx_meth.c
@@ -842,6 +842,7 @@ static const EVP_PKEY_METHOD ed448_pkey_
 
 #ifdef S390X_EC_ASM
 # include "s390x_arch.h"
+# include "internal/constant_time.h"
 
 static void s390x_x25519_mod_p(unsigned char u[32])
 {
@@ -855,16 +856,16 @@ static void s390x_x25519_mod_p(unsigned
     u_red[31] = (unsigned char)c;
     c >>= 8;
 
-    for (i = 30; c > 0 && i >= 0; i--) {
+    for (i = 30; i >= 0; i--) {
         c += (unsigned int)u_red[i];
         u_red[i] = (unsigned char)c;
         c >>= 8;
     }
 
-    if (u_red[0] & 0x80) {
-        u_red[0] &= 0x7f;
-        memcpy(u, u_red, sizeof(u_red));
-    }
+    c = (u_red[0] & 0x80) >> 7;
+    u_red[0] &= 0x7f;
+    constant_time_cond_swap_buff(0 - (unsigned char)c,
+                                 u, u_red, sizeof(u_red));
 }
 
 static void s390x_x448_mod_p(unsigned char u[56])
@@ -889,16 +890,14 @@ static void s390x_x448_mod_p(unsigned ch
     u_red[27] = (unsigned char)c;
     c >>= 8;
 
-    for (i = 26; c > 0 && i >= 0; i--) {
+    for (i = 26; i >= 0; i--) {
         c += (unsigned int)u_red[i];
         u_red[i] = (unsigned char)c;
         c >>= 8;
     }
 
-    if (u_red[0] & 0x80) {
-        u_red[0] &= 0x7f;
-        memcpy(u, u_red, sizeof(u_red));
-    }
+    constant_time_cond_swap_buff(0 - (unsigned char)c,
+                                 u, u_red, sizeof(u_red));
 }
 
 static int s390x_x25519_mul(unsigned char u_dst[32],
@@ -954,7 +953,7 @@ static int s390x_x448_mul(unsigned char
     memcpy(param.x448.d_src, d_src, 56);
 
     s390x_flip_endian64(param.x448.u_src, param.x448.u_src);
-    s390x_x448_mod_p(param.x448.u_src);
+    s390x_x448_mod_p(param.x448.u_src + 8);
 
     s390x_flip_endian64(param.x448.d_src, param.x448.d_src);
     param.x448.d_src[63] &= 252;
Index: openssl-1.1.1d/include/internal/constant_timeh
===================================================================
--- openssl-1.1.1d.orig/include/internal/constant_time.h
+++ openssl-1.1.1d/include/internal/constant_time.h
@@ -353,6 +353,34 @@ static ossl_inline void constant_time_co
 }
 
 /*
+ * mask must be 0xFF or 0x00.
+ * "constant time" is per len.
+ *
+ * if (mask) {
+ *     unsigned char tmp[len];
+ *
+ *     memcpy(tmp, a, len);
+ *     memcpy(a, b);
+ *     memcpy(b, tmp);
+ * }
+ */
+static ossl_inline void constant_time_cond_swap_buff(unsigned char mask,
+                                                     unsigned char *a,
+                                                     unsigned char *b,
+                                                     size_t len)
+{
+    size_t i;
+    unsigned char tmp;
+
+    for (i = 0; i < len; i++) {
+        tmp = a[i] ^ b[i];
+        tmp &= mask;
+        a[i] ^= tmp;
+        b[i] ^= tmp;
+    }
+}
+
+/*
  * table is a two dimensional array of bytes. Each row has rowsize elements.
  * Copies row number idx into out. rowsize and numrows are not considered
  * private.
Index: openssl-1.1.1d/test/recipes/30-test_evp_data/evppkey.txt
===================================================================
--- openssl-1.1.1d.orig/test/recipes/30-test_evp_data/evppkey.txt
+++ openssl-1.1.1d/test/recipes/30-test_evp_data/evppkey.txt
@@ -814,6 +814,8 @@ PublicKeyRaw=Bob-448-PUBLIC-Raw:X448:3eb
 
 PrivPubKeyPair = Bob-448-Raw:Bob-448-PUBLIC-Raw
 
+PublicKeyRaw=Bob-448-PUBLIC-Raw-NonCanonical:X448:ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
+
 Derive=Alice-448
 PeerKey=Bob-448-PUBLIC
 SharedSecret=07fff4181ac6cc95ec1c16a94a0f74d12da232ce40a77552281d282bb60c0b56fd2464c335543936521c24403085d59a449a5037514a879d
@@ -830,6 +832,11 @@ Derive=Bob-448-Raw
 PeerKey=Alice-448-PUBLIC-Raw
 SharedSecret=07fff4181ac6cc95ec1c16a94a0f74d12da232ce40a77552281d282bb60c0b56fd2464c335543936521c24403085d59a449a5037514a879d
 
+# Self-generated non-canonical
+Derive=Alice-448-Raw
+PeerKey=Bob-448-PUBLIC-Raw-NonCanonical
+SharedSecret=66e2e682b1f8e68c809f1bb3e406bd826921d9c1a5bfbfcbab7ae72feecee63660eabd54934f3382061d17607f581a90bdac917a064959fb
+
 # Illegal sign/verify operations with X448 key
 
 Sign=Alice-448