From a2a1b803da77e6a1fe3f059f2059280a97a95ca2 Mon Sep 17 00:00:00 2001
From: Steven Cooreman <steven.cooreman@silabs.com>
Date: Thu, 29 Apr 2021 16:37:59 +0200
Subject: [PATCH] Make safer_memcmp available to all compile units under PSA

Now renamed to mbedtls_psa_safer_memcmp, it provides a single location
for buffer comparison.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
---
 library/psa_crypto.c      | 18 ++----------------
 library/psa_crypto_core.h | 20 ++++++++++++++++++++
 library/psa_crypto_mac.c  | 14 +-------------
 3 files changed, 23 insertions(+), 29 deletions(-)

diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 81770bff9..dbf05b9ec 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -93,20 +93,6 @@
 
 #define ARRAY_LENGTH( array ) ( sizeof( array ) / sizeof( *( array ) ) )
 
-/* constant-time buffer comparison */
-static inline int safer_memcmp( const uint8_t *a, const uint8_t *b, size_t n )
-{
-    size_t i;
-    unsigned char diff = 0;
-
-    for( i = 0; i < n; i++ )
-        diff |= a[i] ^ b[i];
-
-    return( diff );
-}
-
-
-
 /****************************************************************/
 /* Global data, support functions and library management */
 /****************************************************************/
@@ -2235,7 +2221,7 @@ psa_status_t psa_hash_verify( psa_hash_operation_t *operation,
         return( status );
     if( actual_hash_length != hash_length )
         return( PSA_ERROR_INVALID_SIGNATURE );
-    if( safer_memcmp( hash, actual_hash, actual_hash_length ) != 0 )
+    if( mbedtls_psa_safer_memcmp( hash, actual_hash, actual_hash_length ) != 0 )
         return( PSA_ERROR_INVALID_SIGNATURE );
     return( PSA_SUCCESS );
 }
@@ -2271,7 +2257,7 @@ psa_status_t psa_hash_compare( psa_algorithm_t alg,
         return( status );
     if( actual_hash_length != hash_length )
         return( PSA_ERROR_INVALID_SIGNATURE );
-    if( safer_memcmp( hash, actual_hash, actual_hash_length ) != 0 )
+    if( mbedtls_psa_safer_memcmp( hash, actual_hash, actual_hash_length ) != 0 )
         return( PSA_ERROR_INVALID_SIGNATURE );
     return( PSA_SUCCESS );
 }
diff --git a/library/psa_crypto_core.h b/library/psa_crypto_core.h
index 90f9d1863..b75e59a81 100644
--- a/library/psa_crypto_core.h
+++ b/library/psa_crypto_core.h
@@ -30,6 +30,26 @@
 #include "psa/crypto.h"
 #include "psa/crypto_se_driver.h"
 
+/** Constant-time buffer comparison
+ *
+ * \param[in]  a    Left-hand buffer for comparison.
+ * \param[in]  b    Right-hand buffer for comparison.
+ * \param n         Amount of bytes to compare.
+ *
+ * \return 0 if the buffer contents are equal, non-zero otherwise
+ */
+static inline int mbedtls_psa_safer_memcmp(
+    const uint8_t *a, const uint8_t *b, size_t n )
+{
+    size_t i;
+    unsigned char diff = 0;
+
+    for( i = 0; i < n; i++ )
+        diff |= a[i] ^ b[i];
+
+    return( diff );
+}
+
 /** The data structure representing a key slot, containing key material
  * and metadata for one key.
  */
diff --git a/library/psa_crypto_mac.c b/library/psa_crypto_mac.c
index 7122ecdd3..854aee4f0 100644
--- a/library/psa_crypto_mac.c
+++ b/library/psa_crypto_mac.c
@@ -526,18 +526,6 @@ static psa_status_t mac_sign_finish(
     return( status );
 }
 
-/* constant-time buffer comparison */
-static inline int safer_memcmp( const uint8_t *a, const uint8_t *b, size_t n )
-{
-    size_t i;
-    unsigned char diff = 0;
-
-    for( i = 0; i < n; i++ )
-        diff |= a[i] ^ b[i];
-
-    return( diff );
-}
-
 static psa_status_t mac_verify_finish(
     mbedtls_psa_mac_operation_t *operation,
     const uint8_t *mac,
@@ -562,7 +550,7 @@ static psa_status_t mac_verify_finish(
     if( status != PSA_SUCCESS )
         goto cleanup;
 
-    if( safer_memcmp( mac, actual_mac, mac_length ) != 0 )
+    if( mbedtls_psa_safer_memcmp( mac, actual_mac, mac_length ) != 0 )
         status = PSA_ERROR_INVALID_SIGNATURE;
 
 cleanup: