From b9cd19bc8c6196511eb1d10094c62e58e5da6eed Mon Sep 17 00:00:00 2001
From: Dave Rodgman <dave.rodgman@arm.com>
Date: Fri, 30 Dec 2022 21:32:03 +0000
Subject: [PATCH] Prevent perf regressions in mbedtls_xor

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
---
 library/alignment.h     | 13 +++++++++++++
 library/common.h        |  6 ++++--
 library/constant_time.c |  9 ---------
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/library/alignment.h b/library/alignment.h
index bfc965eae1..aa4c430b96 100644
--- a/library/alignment.h
+++ b/library/alignment.h
@@ -29,6 +29,19 @@
 
 #include "mbedtls/build_info.h"
 
+/*
+ * Define MBEDTLS_EFFICIENT_UNALIGNED_ACCESS for architectures where unaligned memory
+ * accesses are known to be safe and efficient.
+ */
+#if defined(__ARM_FEATURE_UNALIGNED) \
+    || defined(__i386__) || defined(__amd64__) || defined(__x86_64__)
+/*
+ * __ARM_FEATURE_UNALIGNED is defined where appropriate by armcc, gcc 7, clang 9
+ * (and later versions); all x86 platforms should have efficient unaligned access.
+ */
+#define MBEDTLS_EFFICIENT_UNALIGNED_ACCESS
+#endif
+
 /**
  * Read the unsigned 16 bits integer from the given address, which need not
  * be aligned.
diff --git a/library/common.h b/library/common.h
index fd3ddba48c..ae6625b9e5 100644
--- a/library/common.h
+++ b/library/common.h
@@ -122,11 +122,13 @@ static inline const unsigned char *mbedtls_buffer_offset_const(
  */
 inline void mbedtls_xor(unsigned char *r, const unsigned char *a, const unsigned char *b, size_t n)
 {
-    size_t i;
-    for (i = 0; (i + 4) <= n; i += 4) {
+    size_t i = 0;
+#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS)
+    for (; (i + 4) <= n; i += 4) {
         uint32_t x = mbedtls_get_unaligned_uint32(a + i) ^ mbedtls_get_unaligned_uint32(b + i);
         mbedtls_put_unaligned_uint32(r + i, x);
     }
+#endif
     for (; i < n; i++) {
         r[i] = a[i] ^ b[i];
     }
diff --git a/library/constant_time.c b/library/constant_time.c
index 309e11cd2b..89778d53ca 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -47,15 +47,6 @@
 
 #include <string.h>
 
-/*
- * Define MBEDTLS_EFFICIENT_UNALIGNED_ACCESS for architectures where unaligned memory
- * accesses are known to be safe and efficient.
- */
-#if defined(__ARM_FEATURE_UNALIGNED)
-/* __ARM_FEATURE_UNALIGNED is defined by armcc, gcc 7, clang 9 and later versions */
-#define MBEDTLS_EFFICIENT_UNALIGNED_ACCESS
-#endif
-
 /*
  * Define MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS where assembly is present to
  * perform fast unaligned access to volatile data.